R-2016-192 2016-10-24RESOLUTION NO. R2016-192
A Resolution of the City Council of the City of Pearland, Texas,
amending the City's Engineering Design Criteria Manual.
BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF PEARLAND,
TEXAS:
Section 1. That the City Council hereby amends the City's Engineering Design
Criteria Manual in accordance with Exhibit "A" attached hereto.
PASSED, APPROVED, AND ADOPTED this 24th day of October, A.D., 2016.
TOM REID
MAYOR
ATTEST:
UNG NG,
Y SE ' ETARY
APPROVED AS TO FORM:
DARR N M. COKER
CITY ATTORNEY
Resolution No. R2016-192
Exhibit "A"
City of Pearland, Texas
Engineering Design
Criteria Manual
September 2016 (Final Draft)
TABLE OF CONTENTS
CHAPTER 1: GENERAL REQUIREMENTS
1.1 General
1.2 Preliminary Research
1.3 Fees
1.4 Design Review Requirements
1.5 Construction Procedure Requirements
1.6 Approval and Acceptance of Public Improvement Projects
1.7 Approvals and Variances
Appendix A: Checklist for Subdivision Acceptance
CHAPTER 2: CONSTRUCTION PLANS AND MISCELLANEOUS REQUIREMENTS
2.1 Required Plan Sheets
2.2 Drawing Requirements
2.3 Easements
2.4 Utility Locations
2.5 Private Facility Locations
2.6 Crossings
2.7 Trench Safety
2.8 Street Lighting
2.9 Bench Marks
2.10 Residential Lots and Improvements
2.11 Flood Plain Management
2.12 Stormwater Management Plan
CHAPTER 3:
WATER SYSTEM DESIGN CRITERIA
3.1 General
3.2 Design Requirements
3.3 Quality Assurance
3.4 Extra Territorial Jurisdiction
CHAPTER 4: SANITARY SEWER DESIGN CRITERIA
4.1 General
4.2 Definitions
4.3 Design Requirements
4.4 Quality Assurance
4.5 Residential Unsewered Building Sites and Septic Tanks
CHAPTER 5: STORMWATER DESIGN CRITERIA
5.1 General
5.2 Drainage Policy
5.3 References
5.4 Definitions
5.5 Storm Sewer and Road -side Ditch Design Requirements
5.6 Hydrology Analysis Overview
5.7 Hydraulic Channel Design Criteria
5.8 Detention System Design
5.9 Miscellaneous Design Considerations
5.10 Easements and Rights -of -Way
5.11 Submittal
5.12 Quality Assurance
5.13 Design Analysis
Appendix A: Detention Storage Volume Calculations for Small and Medium Projects
CHAPTER 6: PAVING DESIGN CRITERIA
6.1 General
6.2 Roadway Classifications
6.3 Geometric Street Design Standards
6.4 Pavement Structure Requirements
6.5 Grading and Layout Requirements
6.6 Traffic Control Devices
6.7 Sidewalks
6.8 Driveways
6.9 Trails
CHAPTER 7: TRAFFICE DESIGN CRITERIA
7.1 General
7.2 Traffic Impact Analysis
CHAPTER 8: STORMWATER MANAGEMENT
8.1 General
8.2 Definitions
8.3 Allowable Stormwater Discharges
8.4 Stormwater Pollution Prevention Plan (SW3P) Requirements
8.5 Best Management Practices
8.6 Post Construction Stormwater Management in New Development and
Redevelopment
8.7 Stormwater and Illicit Discharge Ordinance
CITY OF PEARLAND
CHAPTER 1
GENERAL REQUIREMENTS
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 6 General Requirements
CHAPTER 1
GENERAL REQUIREMENTS
1.1 GENERAL
1.1.1 These Standards describe the general requirements for the preparation of
construction plans and the supporting documents required for approval by
the City of Pearland. Specific design requirements, in addition to these
standards, may be required by the City of Pearland.
1.1.2 Construction plans for public improvements within Pearland city limits
shall be approved by the City of Pearland. Construction plans for public
improvements within the City of Pearland extraterritorial jurisdiction (ETJ)
shall be reviewed and approved by Brazoria County Engineering
Department, respective Municipal Utility Districts, Brazoria Drainage
District No. 4, and City of Pearland.
1.1.3 Construction plans for private improvements that connect to or affect the
public infrastructure shall be approved by the City of Pearland as required
in the Site Development chapter of these standards and the Uniform
Development Code.
1.1.4 All projects that are required to conform to these Standards shall also
comply with all applicable City of Pearland ordinances.
1.1.5 All construction plans and supporting documentation shall conform to the
requirements of these Standards and regulations of all Federal, State,
County, and entities having jurisdiction. It is the responsibility of the
project engineer to use these standards professionally to produce a design
product conforming to acceptable engineering practices.
1.1.6 The office of City Engineer shall review and maintain the Engineering
Design Criteria Manual. Any recommended changes to the Engineering
Design Criteria Manual shall be approved or disapproved by the office of
City Engineer. All approved changes will be summarized and updated to
the Engineering Design Criteria Manual at a frequency determined, but no
less than once every two years, by the office of City Engineer.
1.1.7 The office of City Engineer shall develop and maintain Standard
Construction Details. These Standard Construction Details shall be
maintained and updated periodically by the office of City Engineer. These
documents are available in the office of City Engineer and are available for
review upon request.
Page 2 of 6 General Requirements
1.2 PRELIMINARY RESEARCH
1.2.1 Personnel from our Public Works Department and office of City Engineer
will be available for preliminary meetings to discuss a proposed project with
the project engineer and/or developer. The preliminary meetings are
available if the need for predevelopment meetings is not there, or to further
clarify discussions from the predevelopment meeting. This preliminary
meeting between the City and the engineer/developer should be scheduled
with the office of City Engineer staff before submittal of any documents for
review. Predevelopment meetings should be scheduled through the
Planning Department.
1.2.2 Research of all existing utility and right-of-way information with City,
County, State, and other public and private utility agencies shall be
completed and documented prior to submittal of any plans to the City.
1.3 FEES
1.3.1 Before beginning construction on a project, all applicable fees shall be paid
to the City.
1.4 DESIGN REVIEW REQUIREMENTS
1.4.1 Submit electronic copies of construction plans and supporting
documentation to the office of City Engineer for review. Plans will be
circulated to the appropriate departments for their review. Comments will
be returned to the design engineer in a timely manner. If the project is a
City of Pearland Capital Improvement Project, all correspondence should
be directed to City of Pearland Director of Engineering and Capital Projects.
1.4.2 Based on the trip estimates for the proposed development by the design
engineer, a Traffic Impact Analysis may be required to determine necessary
traffic mitigation measures to maintain the required level of service as
dictated by City regulations and requirements. Refer to Chapter 7 for
further requirements.
1.4.3 Final Drainage plan must be approved and signed by Brazoria Drainage
District No. 4, prior to submitting to City of Pearland for approval.
1.4.4 After all comments have been adequately addressed, submit an electronic
copy of the revised and final construction plans and responses to comments,
with redline plans to the office of City Engineer for approval.
Page 3 of 6 General Requirements
1.4.5 After final approval has been granted, an electronic copy of the plans will
be stamped by the office of City Engineer for approval.
1.4.6 If project is not being platted, then record all easements prior to final
acceptance.
1.4.7 As warranted by scope and type of design, plans should be submitted for
review and approval by Texas Commission on Environmental Quality.
1.4.8 As warranted by scope and type of design, plans should be in compliance
with Texas Accessibility Standards (TAC) and American with Disabilities
Act (ADA) regulations and criteria. Plans should be submitted to an
approved firm for such reviews and approvals.
1.5 CONSTRUCTION PROCEDURE REQUIREMENTS
1.5.1 Construction shall not begin until construction plans are approved by the
Office of City Engineer and until preliminary plat is approved, permits,
bonds, licenses, etc. have been obtained.
1.5.2 Coordinate with the office of City Engineer for the pre -construction meeting
for the project. Department staff overseeing the construction process must
attend the pre -construction meeting, which shall be held at the office of City
Engineer or at the project site.
1.5.3 Notify the office of City Engineer at least forty-eight (48) hours
prior to beginning construction and at least twenty-four (24) hours prior to
each time concrete is placed on the project and prior to all required
inspections or tests. Inspections shall be conducted by the office of City
Engineer staff or any designee as may be provided by the City.
1.5.4 Notify the City Engineer's office at least forty-eight (48) hours prior to any
final inspection.
1.5.5 Within thirty (30) days after completion of the project, the project engineer
shall provide to the City two an electronic file copy (PDF format min. 400
dpi resolution), an AutoCAD Release 12 file (.dwg) or compatible .dxf file,
and a GIS compatible file (see Chapter 2, Section 2.2.30 for more electronic
file options and requirements). Project engineer shall coordinate with the
office of City Engineer on other project completion deliverables such as
Maintenance Bond, Affidavit of Bills Paid, Engineer's Letter of
Completion, applicable test results, etc. (See Appendix A).
1.5.6 Record Drawings (mark-ups) submitted by contractor to the project
engineer for the preparation of official Record Drawings shall include
Page 4 of 6 General Requirements
verification (as applicable) of all manhole and junction box locations, line
sizes and lengths, elevations and inverts, lift station facility changes, fire
hydrants and valve locations, driveways, service lines locations and sizes,
changes to roadway profile and geometrics, etc. Project engineer shall
modify plans accordingly and submit revised electronic plans as Record
Drawings for approval.
1.5.7 All delivery tickets for all materials (e.g., concrete, cement stabilized sand)
shall be maintained by the contractor and upon written request be made
available for review by the office of City Engineer. These delivery tickets
shall be maintained for a maximum of one year from the completion of the
project.
1.5.8 Changes to approved plans shall be approved by the office of City Engineer
prior to construction. Any required changes during construction due to field
conditions or errors shall be discussed with the office of City Engineer for
approval/coordination prior to making the change.
1.5.9 Office of City Engineer shall be on the distribution list for all construction
test results and reports.
1.6 APPROVAL AND ACCEPTANCE OF PUBLIC IMPROVEMENT
PROJECTS
1.6.1 Public Improvement projects shall have final approval by the office of City
Engineer prior to placing the facilities in service.
1.6.2 All items listed in "Appendix A — Final Check List for Subdivision
Acceptance" must be met prior to final approval by the office of City
Engineer.
1.6.3 Final approval will be documented in writing by the office of City Engineer.
1.6.4 Public Improvement projects within the City of Pearland will be subject to
a minimum two (2) year maintenance period. An inspection prior to the end
of the maintenance period shall be conducted by the office of City Engineer
and all other entities having jurisdiction. All facilities shall be operational
and in good condition prior to final acceptance of a project in order to obtain
the refund of the maintenance bond.
1.7 APPROVALS AND VARIANCES
1.7.1 Approvals required in these Standards are the responsibility of the Owner.
Failure to obtain appropriate approvals may be grounds for suspension of
Page 5 of 6 General Requirements
construction until appropriate approvals are granted. Items that do not
conform to these Standards shall be submitted for a variance request.
1.7.2 Specific approval, as required by these Standards, will be requested by the
Owner prior to or at the time of submittal of review plans for the project. In
order to be valid, all specific approval items must be granted in writing by
the office of City Engineer.
1.7.3 Construction work related to any specific approval item that has not been
approved in writing should not begin until the office of City Engineer has
granted written approval. Any work that proceeds without specific approval
will be subject to removal and replacement in accordance with these
Standards.
1.7.4 Materials and manufactured items used in construction of public
improvements shall conform to the City's Standard Specifications.
1.7.5 All projects that are required to conform to these Standards shall also comply
with applicable City Ordinances. Projects should be reviewed for
compliance with the Zoning, Subdivision, Floodplain Management, Signage,
Traffic, Water, Sewer, Stormwater Management, and any other applicable
Ordinances.
Page 6 of 6 General Requirements
Appendix A
Final Checklist for Subdivision Acceptance
FINAL CHECK LIST
FOR
SUBDIVISION ACCEPTANCE
Name of Subdivision:
Name of Developer:
Name of Contractor:
ITEMS
1. Field Compliance
(A) Bench Marks, Brass Caps to be set with following information:
1. Elevation
2. Date of Adjustment
3. Surveyor's number
(B) Location and elevation to be furnished to City
2. Construction Plans:
Developer's Engineer has furnished City with complete set
of scanned recorded drawings for the subdivision on CD
(PDF file format, 400 DPI minimum)
3. Water Distribution Construction Checklist submitted by the
Developer's engineer.
4. Statement from City Tax Collector as to ownership and status
of State, County, School District and City taxes.
5. Two Year Maintenance Bond in amount of 50% of construction
costs.
6. Contractor's affidavit of all bills paid.
7 Cost for two (2) years operating cost for the total number of
Lights installed.
8. All street signs as required within the subdivision.
Page 1 of 2
9. Engineers certification letter.
11. Total linear feet of storm sewer pipe.
12. Total linear feet of sanitary sewer pipe.
13. Total linear feet of concrete streets.
14. Total linear feet of water lines.
4" water line
6" water line
8" water line
12" water line
15. Deposit for building thoroughfare (?).
16. Inspection Fee of 1% with engineer's estimate
(Due at time of platting)
17. Perimeter Sidewalks (6' or 4')
City Engineer
Date:
Page 2 of 2
CITY OF PEARLAND
CHAPTER 2
CONSTRUCTION PLAN AND MISCELLANEOUS
REQUIREMENTS
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 13 Construction Plans and Miscellaneous Requirements
CHAPTER 2
CONSTRUCTION PLAN AND MISCELLANEOUS REQUIREMENTS
2.1 REQUIRED PLAN SHEETS
2.1.1 Cover Sheet
2.1.2 Approved Plat (latest version of the approved plat shall be included in the
Record Drawings)
2.1.3 Construction Notes and Legend
2.1.4 Overall plan Layouts for proposed improvements
2.1.5 Permanent Street Signage Plan
2.1.6 Drainage Area Map and Calculations
2.1.7 Lot Grading Plan showing Existing and Proposed Spot Elevations
2.1.8 Plan and Profiles
2.1.9 Detention Pond Plan and Details, as Applicable
2.1.10 Traffic Control Plans and Details, as Applicable
2.1.11 Pavement Marking and Signage, as Applicable
2.1.12 Specific Construction Details
2. 1.13 Storm Water Pollution Prevention Plans and Details
2.1.14 Standard City of Pearland Construction Details
2.2 DRAWING REQUIREMENTS
2.2.1 The seal, date, and signature of the engineer responsible for preparation of
the plans is required on each sheet in compliance with the rules and
regulations of the Texas State Board of Professional Engineers (TSBPE).
The engineer may use TSBPE-accepted electronic seal, date, and
signature.
2.2.2 A benchmark elevation and description is required on each sheet along
with flood plain information for the project. Date of datum adjustment for
Page 2 of 13 Construction Plans and Miscellaneous Requirements
the benchmark shall be noted in plans. Benchmark should be tied to City
monuments with datum adjustment factor when applicable.
2.2.3 Label each plan sheet as to street right-of-way widths, pavement widths
and thickness, type of roadway materials, curbs, intersection radii, curve
data, stationing, existing utilities type and location, etc.
2.2.4 Stationing must run from left to right except for short streets or lines
originating from major intersection where the full length can be shown on
one sheet.
2.2.5 A north arrow is required on all appropriate sheets and should be oriented
either upward or to the right. This requirement may be waived under the
following conditions: a storm or sanitary sewer whose flow is from west
to east or from south to north and a primary outfall ditch whose flow is
form west to east or from south to north.
2.2.6 Show all lot lines, property lines, rights-of-way lines, and easement lines.
Provide grading elevation at each corner of lot.
2.2.7 A cover sheet shall be required for all projects unless approved by the
office of City Engineer. All plan sheets should be listed by sheet number
on the cover sheet. A vicinity map should always be included to show the
project location. A City of Pearland signature block shall be provided.
Cover sheet should include engineering firm's registrations number.
2.2.8 If a roadway exists where plans are being prepared to improve or construct
new pavement or to construct a utility, this roadway should be labeled as
to its existing width, type of surfacing, and base thickness if available.
2.2.9 Plans prepared for the City of Pearland shall be prepared using permanent
ink, photographic or other approved process on paper. All plans shall be
submitted electronically.
2.2.10 Do not place match lines in intersections.
2.2.11 Service areas shall be delineated on the area map.
2.2.12 All utility lines four inches (4") in diameter or larger within the right-of-
way or construction easement should be shown in the profile view. All
utility lines, regardless of size should be shown in the plan view.
2.2.13 Show flow line elevations and direction of flow of all existing ditches and
culverts.
Page 3 of 13 Construction Plans and Miscellaneous Requirements
2.2.14 Show natural ground profiles along the centerline and each right-of-way or
easement line except as required below. When there is a difference of less
than 0.5 feet, one right-of-way profile is sufficient.
2.2.15 Resolve all known conflicts of proposed utilities with existing utilities.
2.2.16 Plans shall be standard twenty-two inch by thirty-four inch (22"x34"). All
half—size plans shall be to exact half scale. All plans submittal shall be
electronic (minimum 400 DPI to scale)
2.2.17 Details of special structures not covered by approved standard drawings,
such as stream and gully crossing, special manholes, etc., should be drawn
to scale with the horizontal and vertical scales equal to each other.
2.2.18 Plans shall be drawn to accurate scale, showing proposed pavement
typical cross-sections and details, lines and grades, and all existing
topography within the street rights -of way; and at intersections, the cross
street for designing adequate street crossings.
2.2.19 Grades should be labeled for the top of curb except at railroad crossings.
Centerline grades are acceptable only for paving without curbs and
gutters.
2.2.20 Curb return elevations and grades for turnouts shall show in the profile.
2.2.21 Gutter elevations are required for vertical curves where a railroad track is
being crossed.
2.2.22 The surface elevation at the property line of all existing driveways should
be shown in the profile.
2.2.23 Station all esplanade noses affected by proposed construction, both
existing and proposed.
2.2.24 Station all points of curvature, points of tangency, and points of
intersection in the plan view. Station all radius returns and grade change
points of intersection in the profile with their respective elevations.
2.2.25 The standard scales permitted for plans and profiles of paving and utility
plans are as follow:
A. Major thoroughfares or special intersections/situations:
1" = 2' Vertical; 1" = 20' Horizontal
B. Minor Streets:
1" = 5' Vertical; 1" = 50' Horizontal
Page 4 of 13 Construction Plans and Miscellaneous Requirements
or
1" = 4' Vertical; 1" = 40' Horizontal
or
I" = 2' Vertical; 1" = 20' Horizontal
C. The scales described above are the minimum allowable. Larger
scales may be required to show details of construction.
D. Deviations to these scales can only be allowed with the prior
approval of the Engineering Department.
2.2.26 In addition to the plan and profile sheets described above, each set of
construction drawings shall contain paving and utility key drawings
indexing specific plan and profile sheets. Overall layouts may be drawn at
a scale of one inch equals one hundred feet (1" = 100') or one inch equals
two hundred feet (1" = 200').
2.2.27 Standard City details, where applicable, shall be included.
2.2.28 Construction plans shall include a legend describing standard symbols that
may not be described in the plans.
2.2.29 All property ownership and easement information will be shown in the
construction plans with all proper information associated with it.
When ownership, easement, and right-of-way recording information is not
shown on the plat included in the plans, this information shall be shown on
construction plan sheets.
2.2.30 The City shall be provided with a pdf (minimum 400 DPI) of fmal plans
and eventually Record Plans on a CD. Additionally, City shall be
provided with the electronic files of construction plans in one of the
following formats, as appropriate: Geodatabases (personal geodatabase,
file geodatabase, ArcSDE geodatbase), Shape files (.SHP), DXF (release
12 to AutoCAD 2006), DWG (release 12 to AutoCAD 2014), DGN (5.x to
8 Microstation), LizardTech MrSID and MrSID Gen 3 (.SID) Aerial
photos — for raster data (images).
2.2.31 Coordinate points for project controls or various project points as deemed
necessary by the engineer shall be based on Texas Coordinate System,
South Central Zone, NAD 83. Coordinates shall be Surface.
2.3 EASEMENTS
2.3.1 All easements and recording information, existing and proposed, shall be
shown in the construction plans in accordance with Section 2.2.29.
Page 5 of 13 Construction Plans and Miscellaneous Requirements
2.3.2 Storm sewer, sanitary sewer, and water line easements shall be dedicated
for the specific intended use.
2.3.3 Public utility easement requirements for a sixteen -foot (16') easement are
as outlined in the "Typical Utility Location in 10 -Foot Wide and 16 -Foot
Wide Easement Back -to -Back Lots and 14 -foot Perimeter Lots" drawing
prepared by the Utility Coordinating Committee for Metropolitan Area,
Effective June 1, 1971. The public utility easement width for dry
distribution lines may be ten feet (10'). Perimeter easement may be eight
feet (8') by eight feet (8'), provided that the easement is dedicated by
separate instrument or special notes on the plat.
2.3.4 Water line easements — the following minimum width easements are
required when facilities are not located within public street rights-of-way
or water line easements:
A. Fire hydrants located outside of public rights-of-way or water line
easements shall be encompassed by a ten -foot by ten -foot (10'x10')
exclusive, easement. Fire hydrants shall not be located within any
other type of easements.
B. Water meter easements shall be exclusive and should be located
adjoining a public right-of-way or water line easement.
C. Two-inch (2") and smaller meters serving non-residential and multi-
family developments shall be set in five-foot by five-foot (5'x5')
exclusive water meter easements.
D. Three-inch (3") and larger meters shall be set in a minimum of ten -foot
by twenty -foot (10'x20') exclusive, water meter easements.
E. When approved by the office City Engineer, water mains may be
located in easements not adjacent to public street rights-of-way. These
water mains shall be centered in a ten foot (10') wide exclusive
easement restricted to water only.
F. For new construction, any water main, except at a fire hydrant, located
less than five feet (5') from the right-of-way line and within the right-
of-way shall have a water line easement adjoining the right-of-way.
Water line easements adjoining a right-of-way shall have a minimum
width of ten feet (10').
G. Water mains should be located at the center of a ten -foot (10') water
line easement, provided the easement adjoins the public right-of-way.
2.3.5 Sanitary Sewer Easements - following minimum easement widths are
required for the type of service:
A. The width of all exclusive sanitary sewer easements shall be equal to
the depth of the sewer from fmished grade plus two (2) pipe diameters.
Page 6 of 13 Construction Plans and Miscellaneous Requirements
Sewer shall be located in the center of the easement. The minimum
width of a sanitary easement shall be sixteen feet (16') when split
along a lot line, and ten feet (10') wide for easements located within a
single lot.
B. Exclusive sanitary sewer easement adjoining a public right-of-way
shall be ten feet (10').
C. Exclusive easements for force mains of all sizes shall have a minimum
width easement of sixteen feet (16') for a single force main where the
force main is not located adjacent to a public right-of-way. Where the
force main is located in an easement adjacent to public rights-of-way,
the force main may be located at the center of a ten -foot (10')
easement. Where the force main is located less than five feet (5') from
the right-of-way line within the public right-of-way, the minimum
easement width shall be ten feet (10') adjacent to the right-of-way.
D. Combined storm and sanitary sewer easement shall have minimum
widths as required in Section 2.3.6.B for storm sewer easements.
Additionally, the sanitary sewer main, trunk or force main shall be
located such that the centerline of the pipe shall be at least half the
width of the easement, defined in Section 2.3.5.A, but not less than
seven and one-half feet (7.5'), from the edge of the pavement.
E. For combined storm and sanitary sewer easements located adjacent to
public rights-of-way where the sanitary sewer is located along the
outside of the easement, the centerline of the sanitary sewer pipe shall
be at least half the width of the easement defined in Section 2.3.5.A,
but not less than seven and one-half feet (7.5') from the outside edge
of the easement.
F. Where sanitary sewers or force mains are installed in easements
separated from public rights-of-way by other private or utility
company easements, the sanitary sewer easement should be extended
along or across the private utility company easement to provide access
for maintenance of the sewer or force main.
2.3.6 Storm Sewer Easements - the following minimum easement widths are
required:
A. The minimum width shall be twenty feet (20') with the storm
sewer centered in an exclusive easement, except as approved by
the office of City Engineer.
B. For storm sewers greater than ten feet (10') and less than fifteen
feet (15') in diameter or width, the minimum width of an exclusive
easement shall be twenty-five feet (25')
C. For storm sewer greater than fifteen feet (15') in diameter or width,
the minimum width of an exclusive easement shall be determined
by the office of City Engineer.
D. For storm sewers whose depth to flow line is greater than fifteen
feet (15') , add five feet (5') to the minimum easement width
specified in Section 2.3.6.A and /or 2.3.6.B, above.
Page 7 of 13 Construction Plans and Miscellaneous Requirements
E. For all easements specified in Section 2.3.6, a minimum distance
of five feet (5') must be maintained from the easement line to the
outside edge of the storm sewer.
F. Where approvals are granted for a special use or combination
easement located along side lot or back lot, the minimum width
shall be twenty-five feet (25'). The easement width shall meet or
exceed all other easement requirements.
G. For specifically approved storm sewers located in an exclusive
easement adjacent to public rights-of-way, the minimum easement
width shall be ten feet (10'). The easement width shall meet or
exceed all other easement requirements.
2.4 UTILITY LOCATIONS
2.4.2 All utilities shall be underground with the exception of electric primary
lines. The electric primary lines, defined as feeders or three phase lines,
should be located around the subdivision perimeter whenever possible.
2.4.3 Water Main Location
A. All water mains shall be located within a public right-of-way or
within dedicated water main easements. The location of water
mains within a public street right-of-way is described in Chapter 3,
Section 3.2.
B. Water mains shall not be located in combination easements
without the approval of the office of City Engineer.
2.4.4 Sanitary Sewer Location
B. Sanitary sewers of twelve inches (12") or larger in diameter are
usually located within a public right-of-way or an easement
adjoining the right-of-way. Large sanitary sewers shall be located
within the public street right-of-way in accordance with Chapter 4,
Section 4.3. Sanitary sewers may be located in exclusive or
combination easements provided the easement widths comply with
Section 2.3.6.B, above.
C. Sanitary sewers shall not be located in side lot easements without
the approval from the office of City Engineer.
D. Sanitary sewers should be located within the right-of-way between
the property line and the back of curb on the opposite side of the
right-of-way from the water main.
2.4.5 Storm Sewers
A. Storm sewer shall be located in the public street right-of-way in
accordance with Chapter 5, Section 5.5.2.
B. All storm sewer lines shall be located within public rights-of-way
or approved easements. Placement of a storm sewer in side lot and
back lot easements is discouraged. Approval from the office of
City Engineer for the use of side lot or back lot easements for
storm sewers should be obtained prior to plan preparation.
Page 8 of 13 Construction Plans and Miscellaneous Requirements
2.5 PRIVATE FACILITY LOCATIONS (Not Including Landscaping)
2.5.1 Installation of private facilities, including utilities, in public road rights-of-
way and their adjoining easements shall be approved by the office of City
Engineer.
2.5.2 Private facilities shall not conflict with other facilities in the right-of-way
and shall not be located in exclusive easements as required in these
Standards. All structures within the public right-of-way require approval
from the office of City Engineer and shall be located so as to not interfere
with existing or proposed public facilities.
2.5.3 All facilities in the right-of-way shall be located at least two feet (2')
behind the curb and all underground facilities in the right-of-way shall be
located at least two and one-half feet (2.5') below the top of curb on a
public street.
2.5.4 Private facilities shall be constructed in accordance with construction
plans approved by the office of City Engineer.
2.5.5 Landscaping within the public right-of-way or adjoining easements shall
not affect public utilities or traffic visibility.
2.6 CROSSINGS
2.6.1 Highway Crossings - All State and County Roads
A. State maintained Highway and Farm to Market Road crossings
shall be constructed in accordance with the requirements of Texas
Department of Transportation.
B. A water main, sanitary sewer, or force main shall be encased in a
steel pipe casing extending from right-of-way to right-of-way.
C. County road crossing shall be constructed in accordance with the
County's requirements.
D. Where additional right-of-way has been acquired or will be
required for future widening, the casing, where required, should be
carried to within ten feet (10') of each future right-of-way line.
2.6.2 Street Crossings
A. All water main and sprinkler line crossings under major
thoroughfare boulevards shall be encased. For all water mains,
steel casing shall be used, and for fire sprinkler lines PVC pipe,
SDR 26 shall be used. Welded inside coated steel pipe may be
substituted on street crossing, when approved by the office of
City Engineer.
B. Conduits and sewers that do not carry liquid under pressure may be
bored and jacked into place without an encasement pipe.
C. Crossings under existing concrete streets, other than major
thoroughfares and collectors, shall be constructed by boring and
jacking. PVC pipe shall be jacked into place using equipment
designed for that purpose. Water may be used to facilitate the
Page 9 of 13 Construction Plans and Miscellaneous Requirements
boring and jacking operations. Jetting the pipe main into the place
will not be permitted. When conditions exist that warrant open cut
across an existing street, approval by the office of City Engineer is
required.
D. All open cut installations under existing or proposed streets shall
be backfilled as shown in the City of Pearland Standard
Construction Details.
E. All street crossings shall be constructed in accordance with
construction plans approved by the office of City Engineer. All
street crossings shall be inspected by the office of City Engineer.
All street crossings shall meet the requirements of these Standards.
2.6.3 Railroad and Pipeline Crossings
A. For railroad crossings, the carrier pipe shall be encased in steel
pipe casing extending from right-of-way to right-of-way.
B. All construction within the railroad or pipeline right-of-way shall
conform to minimum requirements set out in the agreement with
the owner of the right-of-way and/or easement.
2.6.4 Ditch and Stream Crossings
A. Aerial crossing attached to the bridge structure is preferred by the
City.
B. Where existing or proposed bridges have sufficient space and
structural capacity for installing water mains or conduits (twelve
inches (12") or smaller) under the bridge, but above the top of the
bent cap elevation, such installation will be permitted upon
approval of the construction plans. In all cases, the water main or
conduit shall be above the bottom chord of the bridge and eighteen
inches (18") above the 100 -year water surface elevation. All
conduits attached to a bridge shall be constructed using steel pipe
and shall extend a minimum of ten feet (10') beyond the bridge
bent or to the right-of-way line, whichever is greater. All conduit
attached to a bridge shall be maintained by the owner of the
conduit or will be subject to removal.
C. Separate, free-standing crossings across drainage ways are not
typically allowed. Project engineer to receive prior approval from
the office of City Engineer prior to design if such installation is
necessary.
D. All stream or ditch crossings shall be constructed of steel pipe
from right-of-way to right-of-way.
2.7 TRENCH SAFETY
Trench safety is required for all excavations greater than five feet (5') in depth.
Adequate details for construction in accordance with applicable OSHA
Page 10 of 13 Construction Plans and Miscellaneous Requirements
regulations will be required in all construction plans that are approved by the City
of Pearland.
2.8 STREET LIGHTING
2.8.1 Installation of street lighting shall be mandatory along all public streets in
the City of Pearland. In addition, the installation of street lighting is
strongly encouraged along existing or repaved streets. Street lighting plan
should be coordinated with the office of City Engineer. For areas in the
Extraterritorial Jurisdiction (ETJ) of the City of Pearland, street lighting
shall be required and reviewed by the office of City Engineer in
accordance with these Standards.
2.8.2 The location of street lights will be designed to maintain approximately
200' of spacing and shall be reviewed and approved by the office of City
Engineer.
2.8.3 Private lighting systems may supplement or replace all or a portion of
public street lighting as long as the net result provides equivalent lighting
to the standard set herein. A perpetual entity, such as an incorporated
homeowners association and/or an appropriate private entity, shall notify
the office of City Engineer of its agreement to pay for the operation,
maintenance, and insurance of a private lighting system prior to
installation of the system. The system shall be approved by the office of
City Engineer.
2.8.4 Street lights shall be designed in accordance with the design and
luminance requirements set out by AASHTO in the latest edition of the
Roadway Lighting design Guide. All public rights-of-way street lighting
systems shall include only light fixtures CenterPoint Energy makes
available to the City of Pearland.
2.9 BENCH MARKS
2.9.1 A permanent bench mark shall be set in each subdivision section or at a
spacing of one mile, whichever is greater. The benchmark shall have an
elevation based on the North American Vertical Datum of 1988, 2001
adjustment.
2.9.2 The bench mark elevation and location shall be certified by a registered
public surveyor as a Texas Society of Professional Surveyors (TSPS)
Standard and Specifications for Category 8, TSPS Third Order Vertical
Control Survey.
2.9.3 Accuracy of elevations for benchmarks shall be Texas Society of
Professional Surveyors Category 8, Third Order.
2.9.4 All bench mark locations shall be provided with ties to existing horizontal
and vertical control monuments including coordinates using Texas State
Plane Coordinate System, South Central Zone, NAD 83 for horizontal
control and NAVD 1988 datum, 2001 adjustment for vertical control.
Page 11 of 13 Construction Plans and Miscellaneous Requirements
2.9.5 Bench marks shall be constructed of a brass disc set in concrete as
approved by the office of City Engineer. The concrete footing for the
bench mark shall be eight inches (8") in diameter and three feet (3') deep.
Concrete shall be reinforced with two number four (244) rebars.
2.9.6 The construction plans shall clearly identify the location of the bench
mark and shall include a complete description, coordinates and elevation,
with adjustment date, of the bench mark.
2.10 RESIDENTIAL LOTS AND IMPROVEMENTS
2.10.1 All residential lots shall drain to a public right-of-way directly adjoining
the lot. Drainage from a residential lot to a public right-of-way at the rear
or side of a lot may be permitted provided the drainage system has been
properly designed to accept the flow. Drainage from a residential lot to an
adjoining greenbelt or golf course shall require a public easement for
drainage purposes to be maintained by the homeowner's association or
appropriate entity. Drainage to a private easement shall require prior
approval by the office of City Engineer. Drainage to a private easement
shall be noted on the recorded subdivision plat. Drainage to a Brazoria
County drainage easement shall be approved by Brazoria Drainage
District No. 4.
2.10.2 A lot grading plan showing proposed minimum slab elevations will be
included in the construction plans. If slab elevations do not change, a
notice of minimum elevation will suffice.
2.11 FLOOD PLAIN MANAGEMENT
2.11.1 All development shall conform with the City's Flood Damage Prevention
Ordinance.
2.1 1.2 Amendments to the published flood maps, map revisions and all requests
for changes to the base flood elevation within Pearland city limits shall be
submitted to the office of City Engineer for approval. Technical data
required by the Federal Emergency Management Agency and justification
for the proposed change must be included with all requests. All requests
for changes to the base flood elevation within the City of Pearland
Extraterritorial Jurisdiction (ETJ) shall be submitted to the City of
Pearland Flood Plain Administrator for comments. Modifications to the
floodplain or floodway require a FEMA approved Letter of Map Revision
(LOMR). Modifications to floodway additionally require a FEMA
approved Conditional Letter of Map Revision (CLOMR)
2.11.3 All data submitted shall be prepared under the supervision of a registered
professional engineer and/or a registered public surveyor and shall comply
with all requirements of the Federal Emergency Management Agency.
2.11.4 All development within regulatory floodplain must apply for a floodplain
Page 12 of 13 Construction Plans and Miscellaneous Requirements
development permit. Construction within the floodplain is prohibited until
this permit is approved by the City's Floodplain Administrator.
2.11.5 Per City Ordinance, The Flood Hazard Prevention Ordinance,
lowest floor elevation shall be minimum 1' above base flood elevation.
2.11.6 Building floor elevation shall be 12 inches above the top of curb or 12
Inches above 100 -year floodplain.
2.12 STORMWATER MANAGEMENT PLAN
2.12.1 All development projects irrespective of the size must develop
Stormwater Pollution Prevention Plan and meet City's latest Illicit
Discharge and Stormwater Ordinance. See Chapter 8 - Stormwater
Management for more detail.
Page 13 of 13 Construction Plans and Miscellaneous Requirements
CITY OF PEARLAND
CHAPTER 3
WATER SYSTEM DESIGN CRITERIA
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 16 Water System Design Criteria
CHAPTER 3
WATER SYSTEM DESIGN CRITERIA
3.1 GENERAL
3.1.1 Criteria for the design of water service and water distribution lines are
herein established. All water lines constructed within the City of Pearland
or its Extraterritorial Jurisdiction (ETJ) shall follow these criteria and be in
agreement with the City of Pearland Comprehensive Plan.
3.1.2 Design, construction and sizing of all water mains and appurtenances shall
meet or exceed the requirements of the Texas Commission of
Environmental Quality (TCEQ) as per 30 TAC 290, Texas Board of
Insurance (TBI), and City of Pearland Water Master Plan/model
3.1.3 The public water system shall not extend beyond the individual water meter.
All waterline construction in public rights-of-way up to and including
construction to the water meter shall conform to these standards.
3.1.4 Design and construction shall conform to the City of Pearland construction
details and construction specifications.
3.1.5 The "City of Pearland" for the purposes of these criteria shall consist of all
land within the city limits, and land located within the City's ETJ.
3.1.6 The final decision approving authority for the City of Pearland with respect
to the water system design criteria shall be the Engineering Department.
3.2 DESIGN REQUIREMENTS
3.2.1 Obtain approval from the office of the City Engineer for exceptions or
deviations from these requirements. Exceptions or deviations may be given
on a project -by -project basis.
3.2.2 Lines:
Page 2 of 16
A. Locate water lines within street rights-of-way, or appropriate utility
easement:
a Six-inch interconnected/looped mains shall only be used
with special approval, shall be a maximum of 800 feet long,
and shall be supported on both ends by an 8 -inch main or
larger. No dead end lines shall be allowed.
d. Except when 6 -inch diameter lines are permitted under the
above criteria, all water lines shall have a minimum diameter
of 8 -inches when such runs are used for lines less than 1000
feet long or when such water lines are required to have a fire
hydrant or flushing valve.
e. 10- inch diameter water line is not permitted.
f. Pipe with a min. 12 -inch diameter should be used for lines
greater than 1000 feet in length.
Water System Design Criteria
g.
Dead-end lines:
(1)
Dead-end lines shall not be allowed in subdivisions
with 25 or more connections unless a looped or
interconnecting water main system is not nearby. A
non -looped system within such subdivision requires
prior approval from the office of the City Engineer.
(2) The design of all water distribution systems should
include the opportunity for future looping or
interconnect of any approved or proposed dead-end
line.
(3) Non-residential dead-end lines within public right-
of-way:
(a) On permanent dead-end lines not serving
residential cul-de-sacs, the line shall be 8
inches in diameter and shall not exceed more
than 700 feet in length from the closest
interconnection main line and shall terminate
with a fire hydrant, flushing valve or blow-
off valve.
(b) In temporary dead-end situations or if the
possibility for future extension of the water
line exists do not reduce pipe sizes
successively. Carry 8 -inch diameter pipe to
the last appurtenance or the plug. Place the
last service as near as possible to the end and
install a standard blow off valve and box at
the end of the 8 -inch diameter line. The
maximum length of such a line shall be 700
feet.
(c) In unavoidable permanent dead-end
situations, reduce the sizes of pipe
successively. Carry an 8 -inch pipe to the last
fire hydrant, then use6-inch pipe to the end of
the line and lay6-inch line in accordance with
Article 3.02, Section B, Clause 1, Item b.
Provide a standard two-inch (2") blow off at
the end of the main.
(d) Isolate dead end lines with a line valve.
h. Water line placement in side lot easements shall not be
allowed except by specific approval from the office of the
City Engineer for looping purposes. Where water line
placement is allowed, they may be required to be lined in a
continuous steel casing pipe. When such casing is required
Page 3 of 16 Water System Design Cntena
by the City, extend the casing uninterrupted from building
line to building line. No horizontal or vertical deflections
are allowed. Construct encased water line of restrained joint
PVC pipe to prevent lateral movement. Provide and install
casing spacers and end seals. This item shall only apply to
publicly maintained lines.
B. Refer to standard specifications for water line testing. All cost
associated with the water line testing shall be the responsibility of
the developer.
C. Chlorination: All newly installed water lines shall have to pass
bacteriological testing before being accepted for maintenance by the
City of Pearland. All cost associated with the testing shall be the
responsibility of the developer.
3.2.3 Location
A. Boulevard streets: If approved, public water lines may be located
within the esplanade. Water lines should be located as near the
centerline as possible to avoid conflict with future pavement
widening. The lines should be located in the street right-of-way to
avoid conflict with future pavement widening.
B. Locations within an easement: Locate water lines in the center of a
10 -foot minimum width dedicated water line easement. For location
within side lot easements, the minimum easement width shall also
be 20 feet. The office of the City Engineer may require a wider
easement if the line is to be buried more than 8 feet deep from
natural ground surface at any point in the easement. Obtain approval
from the City of Pearland for lines to be located in smaller or multi-
use easements.
C. When a water line is placed parallel to but not crossing any other
proposed or existing utility line, other than a sanitary sewer, the
water line shall have a minimum of 4 feet horizontal clearance from
the outside wall of the existing utility to the outside wall of the
proposed waterline. Any proposed deviation from these criteria
must first be approved by the office of the City Engineer.
D. A minimum distance of 2 feet shall be maintained from the right-of-
way or easement line to the outside edge of the water line.
3.2.4 Depth of Cover (See Table 3.1)
A. Provide the minimum depths of cover shown in Table 3.1 from the
top of natural ground behind the curb for curb -and -gutter streets, or
from the lowest elevation of the nearby ditch bottom for roadside
ditch street sections whichever is applicable unless a variation is
granted by the office of the City Engineer.
Page 4 of 16 Water System Design Cnteria
B. Whenever possible, changes in grade or alignment to clear utilities
or underground features should be accomplished by deflecting pipe
joints. The maximum designed deflection shall be 1/2 of the
manufacturer's allowable deflection. The use of regular bends for
any change of grade shall not be allowed except when prior approval
is obtained from the office of the City Engineer.
C. If a depth greater than 8 feet is proposed, all joints of PVC pipe shall
be mechanically restrained. All fittings shall be restrained. Where
conflicts are encountered with utilities or other underground
facilities, the depth of cover may be reduced to 2 feet from top of
curb.
Table 3.1
DEPTH OF COVER FOR WATER LINES
SIZE OF LINE
8 -INCH & 6 -INCH
DEPTH OF COVER*
TOP -OF -CURB OPEN -DITCH
4 FEET 5 FEET below ultimate
flowline
12 -INCH & LARGER 5 FEET 5 FEET below ultimate
flowline
*When crossing easements whose owning or governing agency has stricter depth of cover
criteria than that shown in Table 3.1, the stricter of the two shall apply. Where other
agencies have review authority or jurisdiction and have different depth of cover
requirements, the stricter of the two shall apply.
3.2.5 Appurtenances
A. Do not place appurtenances in pavement when the appurtenance
would be covered in whole or in part by pavement. When approved
by the City, gate valves may be placed in sidewalks or paved
roadways provided that the top of the valve box is flush with the
finished pavement.
B. All water system valves shall conform with AWWA standards and
shall include:
a. Cast iron valve boxes are required on all valves less than or
equal to 12 inches. Valve vaults are required on all valves
16 inches and larger.
b. All valves shall be sized to equal the size of the water main
on which it is located.
Page 5 of 16 Water System Design Criteria
C. Valves
a. Spacing — set at maximum distances along the water line as
follows:
(1) 8"&6"-1000 feet
(2) 12" & Larger — 2000 feet
(3) The total number of valves at any water line
intersection shall equal the total number of lines
leading out from the intersection point minus one.
(4) Refer to standard specifications for tapping sleeve &
valve.
b. Location
(1) Valves must be located at street intersections along
the street right-of-way lines projected across the
water line where possible. Tapping sleeve and
valves are excluded from this requirement.
(2) Isolate fire hydrants and flushing valves from the
service main with a valve located in the fire hydrant
or flushing valve lead. This valve should not be
located in the slope or flowline of roadside ditches.
(3) Intermediate valves, not located on the projection of
the right-of-way line, shall be located on the water
line 5 feet from a fire hydrant but shall not be set in
a driveway.
(4) Locate valves a minimum of 10 feet horizontally
away (either direction) from any sanitary sewer
crossing.
(5) Valves located near reducers shall be located on the
smaller diameter pipe.
(6) All water mains shall be valved within the street
right-of-way.
Valves shall not be placed under or within 2 feet of
ultimate pavement, when it is known that the street
will be widened in the future, without prior approval
of the office of the City Engineer.
(7) Valves shall be placed at the end of all water mains
that are to be extended in the future and the main
shall be extended a minimum of two pipe joint past
the valve.
c. Valve Type
(1) All valves shall be Gate Valve
Page 6 of 16 Water System Design Catena
D. Fire Hydrants
a. Spacing
(1) Single family residential development — 500 foot
maximum spacing. However all structures shall be
within 300 feet or locally adopted NFP standard.
(2) All other development — 300 foot spacing.
b. Location in or along street right-of-way
(1) Locate fire hydrants primarily at or near street
intersections.
(2) Locate fire hydrants at the end of a curb radius of a
street intersection, 3 feet behind back of curb or
projected future curb in a curb & gutter road
construction application.
(3) On cul-de-sacs, place fire hydrant in straight section
to avoid conflict with placement of the sidewalk.
(4) On streets with roadside ditches, set the fire hydrants
within 5 feet of rights-of-way lines. Fire hydrant lead
valves should not be located in the slopes or flow
lines of ditches.
(5) Set fire hydrants not located at intersections or block
corners at mid -lot or on lot lines, as extended to
pavement, when located between right-of-way
intersections. These locations may be adjusted 5 feet
either way to avoid driveways or obstructions. In
either case, do not locate fire hydrants closer than 5
feet from driveways.
(6) Provide fire protection on both sides of Major
Thoroughfare and Collector roads.
(7) Fire hydrants are not allowed in esplanades of streets.
(8) On all Texas Department Transportation (TxDOT)
rights-of-way, set the fire hydrants and flushing
valve set -backs from the edge of right-of-way shall
adhere to TxDOT criteria.
c. Location of fire hydrants or flushing valves outside street
rights-of-way and in public easements:
(1) City review and approval is required for all submitted
locations of fire hydrants and flushing valves in all
developments within the City of Pearland and its
ETJ.
Page 7 of 16 Water System Design Cntena
(2) Locate fire hydrant and flushing valves in protected,
easily accessible areas behind curb lines.
(3) For fire hydrants or flushing valves that are located
adjacent to water lines constructed in 10 foot wide
water line easements, the fire hydrant or flushing
valve shall be centered in a minimum 15 foot by 15
foot separate easement.
(4) For non-residential developments in the City of
Pearland, provide isolation valves at each end of fire
loops requiring on-site fire hydrants.
d. Fire hydrant leads shall be designed to have a minimum 4
foot bury where possible. Bends may be used on the fire
hydrant branch to maintain a 4 foot bury or a 3 foot back of
curb set -back.
e. Do not install fire hydrants within 10 feet vertically or
horizontally of sanitary sewers and force mains.
E. Fittings
a. Fittings shall be Ductile Iron, refer to standard specification.
b. Use plugs with retention clamps and carrying the designation
"plug and clamp." Thrust blocking is required for dead-end
lines that are plugged.
c. All water main joints shall be push on joints. Where
required, mechanical joints are allowed for underground
applications.. Only flanged joints shall be used for above
ground waterline installations.
d. All underground fittings are to be double wrapped in 6 mil
plastic.
F. Ductile Iron Pipe
a. Use of ductile iron pipe shall be with prior approval of the
office of the City Engineer. Ductile iron pipe shall be
provided with polyethylene encasement. Provide minimum
2 wraps of 8 -mil polyethylene, or
b. Polyethylene tube encasement shall conform with the
minimum requirements of "Polyethylene Encasement for
Gray and Ductile Cast Iron Piping for Water and other
Liquids," ANSUAWWA C-105, current revision. Soils
within the project shall be tested to adequately determine the
requirements of the encasement. Appendix A of
ANSI/AWWA C-105 shall be consulted where questions
regarding soil conditions and encasement arise.
Page 8 of 16 Water System Design Cnteria
3.2.6 Water Meter Service
A. All water meters 1 or 2 inches shall be installed by the City of
Pearland on custom home residential properties All water meters in
subdivision developments shall be installed by the developer
meeting City's requirements.
B. Vaulted water meter installation shall be undertaken by private
contractors with prior approval from the office of the City Engineer.
C. Stub outs for future water service are not allowed except where part
of a preapproved master plan, site plan development plan or tract
development plan.
D. Minimum size water service line and fittings shall be 5/8 inch meter
with % inch stop at the meter for any single connection for
residential homes. The Chief Building Official and Inspection
Services should be consulted to ensure the proper sized meter is
selected for any proposed service.
E. Water service leads from the water main to the water meter shall be
placed at a minimum 4 foot below final paving elevations.
F. Water meters shall be 1 inch or 2 inch displacement type, magnetic
drive, cold water meters.
G. Meter boxes shall be located just within the public right-of-way.
Location of meters in the ditch of open ditch streets shall be avoided.
Meter boxes shall be installed no more than 2 inches above fmal
natural ground.
H. Back-flow prevention devices shall be installed in line on the private
water meter service line on all commercial developments, irrigation
metered service, and shall be installed in all applications where the
City of Pearland's Plumbing Code and its latest revision so requires.
3.2.7 Water Line Crossings within the City of Pearland
A. Public and private utility crossings other than sanitary sewer: Where
a water line crosses another utility other than a sanitary sewer, a
minimum of 6 inches of clearance must be maintained between the
outside wall of the water line and the outside wall of the utility.
B. Stream or ditch crossings
a. Elevated crossings
(1) Water lines shall be welded steel pipe and shall
extend a minimum of 15 feet beyond the last bend or
to the right of way line, whichever is greater.
(2) Elevated crossings are preferred to underground
crossings.
(3) Use a separate elevated supporting structure for 12
inch and larger water lines. Locate structures a
Page 9 of 16 Water System Design Cntena
minimum of 10 feet from any existing or proposed
structures.
(a) Adequate structural capacity shall have been
calculated and provided for including
considerations for pipe deflection and all
applicable loading.
(b) Clearance for maintenance purposes above
bent cap elevation shall be provided where
elevated water lines are to be run under
bridges.
(4) When approved by the office of the City Engineer,
bridge attachments for elevated water line crossings
may be made instead of separately supported
crossings. Designer to provide support documents
that bridge was designed for such load or provide
analysis sigged and sealed by a professional engineer
that bridge can support such load.
(5) Design elevated crossings with the elevation of the
bottom of the water line 2 feet above the 100 -year
floodplain elevation
(6) Create a high point in the elevated stream or ditch
crossing and provide an air release valve at that
highest point of the water line.
(7) Provide sufficient span length to accommodate the
cross section of future widening of the stream or
ditch to ultimate cross section.
(8) Base the columns' support designs on soil capacity,
spacing, loading, and all pertinent structural
requirements.
(9) Spacing of supports shall consider effect of support
on channel hydraulics and be subject to city
approval.
(10) Provide pedestrian pipe guards on elevated
crossings.
b. Underground Crossings
(1) Provide a minimum 4 foot clearance from the top of
the pipeline to the ultimate flow line of the ditch.
(2) Provide sufficient length to exceed the ultimate
future development of the stream or ditch.
(3) Water lines shall be C-900 PVC or ductile iron pipe
(if approved by the office of the City Engineer) and
shall extend a minimum of 15 feet beyond the last
bend or to the right of way line, whichever is greater.
Page 10 of 16 Water System Design Criteria
(4) Where other agencies have review authority or
jurisdiction and have different underground crossing
requirements, the stricter of the two shall apply.
C. State Highway and County Road Crossings
a. Extend carrier pipe from right-of-way to right-of-way.
b. The approval of the design by the appropriate governmental
agency shall be demonstrated to the office of the City
Engineer before plans will be approved.
c. Where additional right-of-way has been acquired for future
widening, the casing shall extend 5 feet beyond each right-
of-way line.
D. Railroad Crossings
a. For mainline and spur line railroad crossings, the water line
shall meet the requirements of the governing agency and
such requirements shall be followed from 5 feet beyond each
right-of-way line and across the right-of-way itself. Any
deviation must be approved by the railroad companies. The
approval of the design by the appropriate governing agency
shall be obtained and submitted to the office of the City
Engineer before plans will be approved.
b. Where there is no railroad but a railroad owned easement or
right-of-way, as a minimum extend a steel casing from right-
of-way to right-of-way line.
c. The approval of the design concept by the railroad involved
must be obtained and submitted to the office of the City
Engineer before plans will be approved.
E. Additional Requirements
a. Isolate water lines from casing with spacers and supports.
b. The carrier pipeline shall extend a minimum of 1 -foot
beyond the end of the casing to allow flanged joints to be
constructed if necessary.
F. Oil and Gas Pipeline Crossings
Use PVC pipe when crossing a non -service transmission pipeline
regardless of depth. Designer is required to meet with the office of
the City Engineer to discuss possible HDPE encasement for the PVC
water main. All non -service transmission pipeline crossings must
have the approval of the company whose lines are being crossed.
Maintain a minimum 2 foot vertical separation between the pipeline
and the water line.
Page 11 of 16 Watcr System Design Criteria
G. Fire flow Waterline Loops within Non -Residential Developments
For non-residential developments inside the City of Pearland and
requesting on-site water mains, comply with the following
requirements to allow maintenance and future repair operations if
the City of Pearland will be the entity maintaining the water main:
a. Avoid laying any new water lines under proposed or existing
pavement but where unavoidable, provide minimum 10 foot
expansion joints (free joints) in the easement over the water
line.
b. Fire flow waterline loops within non-residential
developments that are to be maintained by the City of
Pearland shall be placed in a water line easement that shall
be dedicated to the City.
c. There shall be no structures or equipment pads constructed
over a publicly maintained water line.
3.2.8 Auger Construction: Use the following general criteria for establishing
auger, bore and jack, or microtunneling sections when site conditions
require their use:
A. Improved streets — Use auger or microtunneling construction to
cross a street regardless of surface. Auger or microtunneling length
shall be computed as roadway width at the proposed bore location
plus a minimum of 10 feet to either side of roadway.
B. Driveways — Use auger or microtunneling construction to cross
improved driveways. Bore and jack, auger or microtunneling length
shall be a minimum of the driveway's width.
C. The office of the City Engineer shall be consulted for an auger
pit/bore pit backfill details.
3.2.9 Circulation and Flushing for Water Quality: The layout of the water
distribution system shall provide for maximum circulation of water.
A. Provide a source of fresh water at each end or at multiple points of
a subdivision or development. Provide ways to create circulation
and place valves and fire hydrants to allow simple flushing of lines.
B. Where stubs are provided for future extensions, isolate the stubs
with a valve and no service connections will be allowed beyond the
valve before the line is extended. Place two full joint of pipe
between the valve and the plug.
3.2.10 New Water Lines Constructed Near Sanitary Sewers and Force Mains and
Manholes
Page 12 of 16 Water System Design Criteria
A. New Water Lines Parallel to Sanitary Sewer and Force Mains:
Locate water lines a minimum of 9 feet horizontally, outside wall to
outside wall, when parallel to sanitary sewers and force mains. Use
the following procedure when site conditions prohibit achieving 9
feet of separation:
a. When a new water line is to parallel an existing sanitary
sewer force main or gravity sewer and the 9 foot minimum
clear separation cannot be achieved, the existing sanitary
sewer shall be replaced with SDR -26 pipe with pressure
gaskets, or PVC C-900 150 psi pipe or better and equipped
with pressure type joints.
b. The water lines and sanitary sewer shall be separated by a
minimum vertical distance of 2 feet and at least 4 feet
horizontally (per 30 TAC 290.44) measured between the
nearest outside walls of the pipes, where the water line shall
always be located above the sewer.
B. New Water Lines Crossing New and Existing Sanitary Sewers and
Force Mains
a. No protection is required if the sanitary sewer is 9 feet below
the water line.
b. Use the protective requirements given in Table 3.2 and 3.3
for sanitary sewer crossings not 9 feet below the water line.
C. Sanitary Sewer Manholes: Provide a minimum 9 foot horizontal
clearance from outside wall of existing or proposed manholes, make
manholes and connecting sewers watertight and test for leakage. If
a 9 foot clearance cannot be obtained, the water line may be located
closer to the manhole when prior approval has been obtained from
the office of the City Engineer by using one of the procedures
below; however, in no case shall the clearance be less than 4 feet.
a. The office of the City Engineer may require the water line to
be encased in a casing when site conditions dictate or when
the water line is within 5 feet of a manhole. The carrier pipe
shall be a minimum of 1 joint of 150 psi pressure class pipe
at least 18 feet long and two nominal sizes larger than the
water conveyance pipe.
b. The water line may be augured, bore & jacked, or
microtunneled past the manhole with at least one 18 foot
section of 150 psi pressure pipe installed centered about the
existing sanitary manhole with pressure grouting of the
annular space using a bentonite/clay mixture or other
commercial grouts.
Page 13 of 16 Water System Design Critena
PRIMARY
CONDITION
SECONDARY
CONDITIONS
IF THE
CLEARANCE IS
*Protection
Requirement
Table 3.2
WATER LINE — SANITARY SEWER CROSSINGS
PROPOSED WATER
EXISTING SANITARY
WATER OVER
SANITARY
Less
than 2'
1
Greater
than 2'
but less
than 9'
2
WATER UNDER
SANITARY
Less
than 2'
3
Greater
than 2'
but Tess
than 9'
4a or 4b
PROPOSED WATER
PROPOSED SANITARY
OR
EXISTING WATER
PROPOSED SANITARY
WATER OVER WATER UNDER
SANITARY SANITARY
Less
than 2'
5
Greater Less
than 2' than 2'
but Tess
than 9'
6a 3
*PROTECTION REOUIREMENTS FOR SANIT/4RY 5EWEIVIROMINGS
(All clearances shall be measured from outside wall to outside wall)
Greater
than 2'
but less
than 9'
6b & 6c
1. One 20 -foot joint of C-900 or C-905 PVC, 150 psi centered over sanitary sewer; 6 -inch minimum
clearance.
2 If no evidence of sanitary sewer leakage, center one joint of water line over sanitary sewer; 24 -inch
minimum clearance If the sewer line is leaking, the sewer line shall be replaced with 150 psi
pressure PVC pipe or other approved pressure pipe with appropriate adapters on all portions of
the sanitary sewer within 9 feet of the water line.
3. Not allowed.
4. a. Auger, bore &jack or microtunnel 9 feet minimum each side of sanitary sewer. Place
one 20 foot joint of C-900 or C905, 150 psi, centered under sanitary sewer. Fill bore hole
with bentonite/clay mixture or grout; 2 foot minimum clearance.
b. OR replace the existing sanitary sewer with C-900 or other approved pressure pipe with
appropriate adapters on all portions of the sanitary sewer within 9 feet of the water line
5. Minimum 18 foot joint of sanitary sewer, C-900 or other approved pressure pipe centered at the
water line, 6 inch minimum clearance. Also center an 18 foot joint of waterline over the sanitary
sewer line. The sanitary sewer line shall be embedded in cement stabilized sand for one pipe
segment plus 1 foot beyond each joint.
6. a. Center a minimum 18 foot joint of sanitary sewer, 150 psi, C-900
or other approved pressure pipe on water line.
b. Use cement stabihzed sand backfill for all portions of the sewer within 9 feet of the
waterline, as measured perpendicularly from any point on the water pipe to the wastewater
pipe (minimum 2.5 sacks cement per cubic yard of sand). The cement -stabilized sand
bedding shall start at a point 6 inches below the bottom of the sanitary sewer to 6 inches
above the top of the sanitary sewer and one quarter of the pipe diameter on either side of
the sewer.
c. Center a minimum 18 footjoint of waterline on the sanitary sewer line.
Page 14 of 16 Water System Design Criteria
PRIMARY
CONDITION
SECONDARY
CONDITIONS
IF THE
CLEARANCE IS
*Protection
Requirement
Table 3.3
PROTECTION REQUIREMENTS AT
WATER LINE — FORCE MAIN CROSSINGS
PROPOSED WATER
EXISTING FORCE MAIN
WATER OVER
FORCE MAIN
Less
than 2'
1
Greater
than 2'
but less
than 9'
2
1
WATER UNDER
FORCE MAIN
Less Greater
than 2' than 2'
but Tess
than 9'
3 4a or 4b
PROPOSED WATER
PROPOSED FORCE MAIN
OR
EXISTING WATER
WARM OW(TER UNDNER
FORCE MAIN FORCE MAIN
Less Greater Less
than 2' than 2' than 2'
but less
than 9'
5 6a
*PROTECTION REQUIREMENTS FOR FORCE MAIN CROSSINGS
(All clearances shall be measured from outside wall to outside wall)
Greater
than 2'
but less
than 9'
6a & 6b
1. Construct waterline with a 20 -foot of C-900 or C-905 PVC pipe section with all related
appurtenances centered above the force main; 6 -inch minimum clearance.
2. Construct water line with one 20 foot joint of C-900, C-905 PVC centered above the force main.
3. Not allowed
4. a. Auger, bore &jack or microtunnel 9 feet minimum each side of force main. Place one
20 -foot joint of C-900 or C905, 150 psi, centered under sanitary sewer. Fill bore hole
with bentonite/clay mixture or grout; 2 foot minimum clearance.
b. OR replace the existing force main with 150 psi C-900 PVC pipe with appropriate
adapters on all portions of the force main within 9 feet of the water line.
5. Center a minimum 18 foot joint of force main, 150 psi C-900 PVC pipe under water line and use
cement -stabilized sand backfill for all portions of the sanitary sewer force main with 9 feet of the
water line as measured perpendicularly from any point on the water pipe to the sanitary sewer force
main pipe (minimum 2.5 sacks cement per cubic yard of sand). The cement -stabilized sand bedding
shall be from a point 6 inches below the bottom of the sanitary sewer force main to 6 inches above
the top of the sanitary sewer force main and one quarter of the pipe diameter of the sanitary sewer
force main on either side of the sanitary sewer force main.
6. Minimum 18 foot of sanitary sewer force main, 150 psi C-900 PVC pipe centered at the water line.
3.3 QUALITY ASSURANCE
3.3.1 Prepare calculations and drawings prepared under the supervision of a
Texas Professional Engineer trained and licensed under the disciplines
required by the nature of the drawings. The final design drawings, must be
sealed, signed and dated by the Professional Engineer responsible for
development of the drawings.
3.3.2 For Elevated Stream and Ditch Crossings: Prepare design calculations for
support columns and column spacing.
Page 15 of 16 Water System Design Cntena
3.4 EXTRA TERRITORIAL JURISDICTION
The criteria herein described in this chapter shall be applicable to all water main
and appurtenance construction and all devices thereunto related within the City of
Pearland but not required for projects located within the ETJ. For those projects
located in the ETJ, the City of Pearland will review pubic improvement
construction drawings and make recommendations that satisfy the City's Standards
for future annexation.
Page 16 of 16 Water System Design Criteria
CITY OF PEARLAND
CHAPTER 4
SANITARY SEWER DESIGN CRITERIA
FINAL. DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 16 Sanitary Sewer Design Criteria
CHAPTER 4
SANITARY SEWER DESIGN REQUIREMENTS
4.1 GENERAL
4.1.1 Criteria for the design of sanitary sewer systems.
4.1.2 This chapter addresses the design of the sanitary sewer systems to be located
within the public right-of-way or a dedicated public easement. Sanitary
sewers located on private property, that are not in a dedicated public
easement, shall not be considered part of the publicly maintained sanitary
sewer system.
4.1.3 On a case-by-case basis the City of Pearland reserves the right to allow
deviations from these design criteria where necessary. See chapter 1 for
procedures to apply for variances to these design criteria. These design
criteria are not intended to cover repairs to pre-existing facilities especially
when such repair work is performed by City of Pearland personnel/forces.
These criteria are not intended to cover existing sanitary sewer facilities
located in alleys or other areas that do not conform to these criteria.
4.2 DEFINITIONS
4.2.1 Public Sanitary Sewer - All sewers that are maintained by the City of
Pearland and located in public easements or street rights-of-way, pre-
existing sanitary sewer lines that are serving the public at the time of the
adoption of these regulations, and new sanitary sewers that are installed in
accordance with these standards.
4.2.2 Sanitary Sewer Main — A sewer which receives the flow from one or more
lateral sewers.
4.2.3 Lateral Sewer — A sewer running laterally down a street, alley or easement
which receives flow from abutting property.
4.2.4 Service Lead — A sewer which branches off of a public sewer and extends
to the limits of the public right-of-way. It shall be construed as having
reference to a public sewer branching off from a main or lateral sewer to
serve one or more houses, single family lots, or other types of small land
tracts situated in the same block, but not directly adjacent to the main or
lateral sewer. A service lead shall never exceed 100 feet in perpendicular
length from the intersecting sewer main or lateral. If the sewer is designed
to serve more than two houses, or the equivalent of two single family
Page 2 of 16 Sanitary Sewer Design Cnteria
residences along a street, a lateral sewer as defined above shall be
constructed.
4.3 DESIGN REQUIREMENTS
4.3.1 Drawings to be Furnished
A. Before any sanitary sewer main or lateral sewer is constructed and
before the City will approve any proposed sanitary sewer for
construction, plan -and -profile sheets of the proposed sanitary sewer
shall be prepared and submitted to the office of the City Engineer
for approval.
B. Drawings shall include at a minimum layout sheets , plan -and -
profile sheets, and details sheets for special items.
C. Sanitary sewers shall conform to the City's Wastewater Master
Plan/model for orderly expansion of the system.
4.3.2 Details to be Shown on Drawings:
A. The construction drawings shall show at a minimum the exact
location of the proposed sanitary sewer in the right-of-way, alley, or
dedicated easement with respect to the edge of the particular right-
of-way, survey base line, any nearby utilities, 100 -year floodplain
elevation within the project area, major landscaping, and other
structures (above ground and below ground) within the construction
site.
4.3.3 Sanitary Sewer Mains and Lateral Sewers
A. Sanitary sewers shall be identified by number, letter, or other
identification as shown on the sanitary sewer layout sheet and
manholes shall be identified by letter or number.
B. Sanitary sewers in curved easements, easements defined by property
lines, and combined easements containing other public utilities must
be shown in both plan and profile views.
C. The profile shall show other underground and surface utilities and
facilities, both in parallel and at crossings; the size, grade, and type
of pipe of the proposed line, the elevations of the proposed line to
the hundredths of a foot at manholes, changes of grade and clean
outs where allowed; and the proposed finished grade over the sewer
with elevations. Where proposed fill or cut is contemplated, the
proposed new natural ground line should be shown as a separate line
from the pre-existing natural ground line. Bedding and backfill shall
comply with City of Pearland standard specifications and standard
details where applicable.
Page 3 of 16 Sanitary Sewer Design Cnteria
D. The construction drawings shall show the existing natural ground
line at either the right-of-way or edge of easement, m addition to
centerline of the pipe, when the proposed sanitary sewer is to be
placed:
a. Between the existing pavement and the right-of-way line.
b. Between existing pavement and an existing or proposed
easement.
E. When a sanitary sewer is located under existing pavement, then the
finished elevations of the pavement shall be shown on the
construction drawings.
4.3.4 Plan and Profile Required for Sewer Mains
A. Sanitary sewer overall layout sheets for single family residential
subdivisions should use a standard engineering scale large enough
to show the entire project on one and no more than two standard
22"x34" sheets. In all cases, the following information must be
shown on the layout:
a. All easements containing or buffering sanitary sewers.
These corresponding recordation information including but
not limited to the corresponding file number for the
easement.
b. Sanitary sewer sizes are shown at points of size change and
between all manholes.
c. All manhole locations.
d. The sanitary sewer alignment shall accurately reflect in the
plan and profile sheets the location of the sanitary sewer as
shown on the detailed plan view. Alignment shall be
stationed with 100 -ft. stations.
e. Service leads that cross street pavement or serve adjacent
property are to be shown on the overall layout.
f. The number, size, and layout of the lots depicted on both the
overall sanitary sewer layout sheet and the individual plan -
and -profile sheets shall match the number and size of the lots
depicted on the final plat after recordation.
g. The direction of flow for existing and proposed sanitary
sewers shall be shown on the overall sanitary sewer layout
sheet.
h. The location of the proposed sanitary sewer within either the
public right-of-way or a dedicated easement.
i. The overall sanitary sewer layout sheet shall show the area,
in acres or in number of lots plus any acreage outside the
project area, which the proposed sewer is designed to serve.
Page 4 of 16 Sanitary Sewer Design Criteria
Include a vicinity map which references the project or lots to
nearby major thoroughfares.
B. Commercial sanitary sewer layouts shall follow the same overall
layout sheet format.
C. Horizontal and vertical scales for the detailed plan -and -profile views
shall be confined to standard engineering scales.
D. The plan view shall show, at a minimum, all of the following
information for the project area:
a. Topographical features.
b. Stationing for the proposed sewers.
c. All existing utilities including gas, power, telephone, fiber
optic, cable etc.
d. Any significant landscaping or other structures which might
impact construction or construction -related activities.
e. The width and type of existing and/or proposed easements.
f. Proposed service leads.
g. The limits of any proposed bore and jack, microtunnel, or
auger operations.
h. Locations where pressure pipe is to be installed for water line
crossings.
i. The proposed sanitary sewer with pipe diameter, length,
material type, and grade clearly labeled.
E. The profile view shall show, at a minimum, all of the following
information for the project area:
a. Underground and surface utilities/facilities which are either
parallel to the proposed sanitary sewer or cross the proposed
sanitary sewer within the construction site.
b. The proposed sanitary sewer's diameter, grade, length, and
material type for each section between manholes. This shall
be labeled on every applicable page and identified as
"proposed."
c. The flowline elevation and centerline station for every
sanitary sewer at every manhole.
d. The top of rim elevation of affected existing and proposed
manholes.
e. The flowline elevation and centerline station at each sheet
break.
f. The type of pipe bedding and backfill shall comply with City
of Pearland standard specifications and standard details
where applicable.
g. The finished grade for proposed and existing pavement.
Where cut and fill are proposed, the proposed new natural
Page 5 of 16 Sanitary Sewer Design Criteria
ground line should be shown as a separate line from the
existing natural ground line.
h. The existing natural ground line at the centerline of the
sanitary sewer when a sewer is to be placed between the edge
of pavement and the public right-of-way. In the cases where
roadside ditches exist, the centerline elevations of the
roadside ditch shall be shown.
i. The existing ground line at the centerline of the proposed
sanitary sewer where a sanitary sewer is to be placed within
an existing easement. Show any proposed cut and fill as
described above.
j. The limits of any proposed bore and jack, microtunnel, or
auger operations.
k. Locations and limits of where pressure pipe is to be installed
for water line crossings.
1. The location of special backfill and any proposed stacks
shall be identified by stations indicated on the design plans.
m. Avoid vertical breaks in profiles. Use alternate scale for all
profile sheets if all of proposed sanitary sewer cannot be
shown on any one profile section for the station run indicated
in plan view for that sheet.
F. All construction drawings for new sanitary sewers shall show the
proposed location, by stations and offsets, of all service leads, and
service connection risers.
4.3.5 Service Lead Construction for Residential and Commercial Developments
A. Space the location of service leads so as to limit the number of
service lead taps to the lateral sewer or sewer main. Service leads
should be spaced at every other property line between two adjoining
residential lots unless there is an odd number of lots. The City
reserves the right to direct the engineer to relocate any proposed
service lead upon reviewing any submitted plans. A single 6 -inch
service lead located at the property line between two adjoining
residential lots would serve two single-family residences with a wye
placed at the end of the service lead. The wyes shall be located at
the private property line.
a. Near side double sewer service leads shall not exceed 5 feet
in length, shall terminate at the property line, and shall be
located within the public right-of-way or dedicated
easement.
b. In cases where the sanitary trunk main is farther than 5 feet
from edge of the right-of-way, a single 6 -inch service shall
be run from the sewer main to the edge of the right-of-way
whereupon a wye shall be placed at the end of service lead,
if 2 lots or parcels are to be served. This shall apply to
Page 6 of 16 Sanitary Sewer Design Criteria
residential sanitary service leads and not to commercial
service taps.
B. Any far side service lead of more than 100 feet perpendicular to the
street right-of-way shall, at the City's discretion, be treated as a
lateral sewer.
C. Service leads for single-family developments shall connect to the
main line.
D Commercial or industrial service leads expected to discharge more
than 5,000 gallons -per -day shall discharge directly into a proposed
or existing sanitary sewer manhole at the flow line without a drop
manhole. Any variance from this requirement shall have prior
approval from the office of City Engineer.
a. Service leads shall be provided to serve each lot or parcel
within a proposed residential, commercial or industrial
development. The detail for a typical near -side and far -side
service leads shall be included with the construction
drawings.
b. Service leads shall be a minimum of 6 inches in diameter
where two or more lots or parcels are served. If the
perpendicular length of a service lead exceeds 100 feet, the
minimum diameter shall be 6 inches and a manhole shall be
utilized for connection to the public sewer. The use of 8 inch
leads may, at the discretion of the City, be reviewed upon
submittal of the construction drawings as a lateral sewer line.
c. In such cases where a service lead is proposed to run
diagonally across the street, prior approval from the office of
the City Engineer must be obtained.
d. Service leads with a diameter of 6 inches shall utilize full
body fittings be they extruded or factory -fabricated for
connection to a proposed public sewer or an approved
saddle -type connector for connection to an existing public
sewer.
e. For residential connection, PVC saddle -type connectors with
gasket and stainless steel straps shall be installed with the
stub oriented 45 degrees from the springline. Tees may be
oriented the in the same manner.
f. For commercial developments connection shall be full-body
tee.
g. The service lead shall be placed so as to minimize the use of
bends as site conditions permit.
h. For existing residential lots (which are not served in
accordance with these guidelines) that need a service lead, if
the distance to the nearest existing sanitary sewer is less than
60 feet, the service lead may be a 4 inch line if only one lot
or parcel is to be served. Commercial and industrial lots and
Page 7 of 16 Sanitary Sewer Design Cnteria
parcels shall have a minimum 6 inch line under the same
conditions.
The location where the service lead or its wye meets the
property line shall be shown on the plans and as-builts, and
marked in the field as shown on the standard details. There
shall be a riser placed where the service lead meets the
property line so that the service lead stub -out can be
recovered at the time that the connection to the service lead
is made.
j. All service leads shall be installed at the time of the
construction of the sanitary sewer in new residential
subdivisions.
4.3.6 General Requirements
A. A licensed plumber shall be responsible for connecting private
residential sanitary sewer service to the public sanitary sewer
system, to wyes and/or tees or to lateral sewers as indicated on the
plans. Said licensed plumber shall be responsible for a properly
installed and watertight private residential service connection.
B. Commercial service connections to the public sanitary sewer with
more than 5,000 gallons per day flow, shall be made at manholes.
Service connection at a concrete manhole should have a rubber boot
that is cast into manhole or service connection should be cored. If
cored, opening must be secured with "Linkseal", grouted and
manhole coating shall be repaired.
C. Materials and construction shall conform to the City of Pearland
Standard Specifications and Standard Details.
D. All constructed sanitary sewer lines shall be air tested for leaks and
a mandrel pulled for structural defects. All sanitary sewer testing
shall comply with or exceed the procedures and qualifications listed
in Texas Administrative Code, Chapter 217, Section 217.57. All
sanitary manholes shall pass a vacuum testing per Chapter 217,
Section 217.58. Upon successful completion of air testing and prior
to placing the sanitary sewer lines in operation, all constructed
sanitary sewer lines shall be videoed. Every joint shall be videoed
360 degrees. A copy of video on DVD shall be submitted to the
office of the City Engineer. Lines and joints shall be corrected if
warranted from video inspection. For procedures and requirements
for the video inspection, refer to City's Standard Specifications.
E. All public sanitary sewers and service leads shall have bedding and
backfill that shall comply with or exceed City of Pearland Standard
Specifications and Details. Those sanitary sewers that are bore and
jacked, microtunneled, augured, or encased in a steel pipe may
require special bedding and backfill.
F. Backfill shall be in accordance with Standard Details.
Page 8 of 16 Sanitary Sewer Design Criteria
G. Public sanitary sewers and force mains shall be located in either the
public right-of-way or dedicated easements. Side lot and back lot
easements should be avoided. Side lot and back lot easements may
be granted special approval from the office of the City Engineer only
when a sanitary sewer located in the street right-of-way is
impossible from an economic and engineering standpoint.
a. Lateral Location of Sewer in Right-of-Way/Easement
(1)
The location of the sanitary sewer within a dedicated
easement shall be along the centerline of the
proposed dedicated easement or as close to the
centerline as can be designed. In those instances
where the dedicated easement is adjacent to the
public right-of-way, the lateral location of the
sanitary sewer shall be at the discretion of the Design
Engineer with approval from the office of the City
Engineer.
H. The final determination as to that portion of a street, alley, or
dedicated easement to be occupied by a proposed sanitary sewer
rests with the office of the City Engineer. The office of the City
Engineer will take into consideration existing, planned and proposed
facilities such as manholes, pavement, pipes/conduits, along with
existing trees and shrubs, historical features, wetlands or other
unique surface conditions when arriving at a decision.
The drawings of the sanitary sewer shall show the location of any
existing pipe or duct that might interfere with the construction of the
sanitary sewer and call to the attention of the office of the City
Engineer any known obstacles that might be encountered in
constructing the sanitary sewer in any location under consideration.
The Professional Engineer of Record shall determine the existence
of pipes, ducts, obstacles and other utilities (i.e. gas, telephone,
electric, fiber optic, cable, etc.) from a visual survey on the ground
plus research of the public records and private records when
available.
J. Sanitary sewers within the City of Pearland's jurisdiction shall be
designed and installed at such a size and depth as to allow for orderly
expansion of the system, so as to avoid duplication in the future.
K. Sanitary sewers shall be separated from water lines by a minimum
of 9 feet of horizontal clearance. See Chapter 3 - Water System
Design Criteria for water and sanitary sewer crossing design criteria.
L. Sanitary sewers shall be separated from storm sewer lines by a
minimum of 4 feet of horizontal clearance and the storm sewer line
shall be above the sanitary line where possible, unless prior approval
from the office of the City Engineer is granted
Page 9 of 16 Sanitary Sewer Design Cntena
M. For sanitary sewers crossing utilities other than water or storm sewer
(i.e. cable, gas, fiber optic, power, etc.), a minimum of 12 inches of
horizontal and vertical clearance shall be maintained as measured
from outside wall to outside wall, where possible.
4.3.7 Line Size
A. The minimum pipe diameter for a public sanitary sewer main or
lateral sewer other than a service lead shall be 8 inches.
B. Service leads 6 inches in diameter shall not serve more than the
equivalent of 2 single family lots or other equivalent types of small
land tracts.
C. Service leads for single family residential lots shall have a minimum
grade of 0.70% for a 6 -inch line.
D. The average daily flow for the design of sanitary sewers shall be
based on minimum 320 gallons per equivalent single-family
connection and a peaking factor ranging from 3 to 5. Designer to
determine the total equivalent connections based on the residential,
commercial, or industrial development being proposed. Submit
documents on proposed connections, flows and sizes to the office of
City Engineer for review and approval.
E. For commercial service leads , the required size of the line shall be
established from the plumbing drawings. Commercial, industrial,
and office areas shall be designed for an average daily flow that can
be anticipated from the contributing area.
F. Commercial sewer service leads shall be 6 inch pipe or larger. A
single 6 inch commercial service connection shall not serve more
than one commercial lot or parcel. Four inch service leads for
commercial developments shall not be allowed.
G. Sewer mains and lateral sewers shall meet at a manhole. Sewer
mains and lateral sewers shall end in a manhole and may end in a
cleanout with special permission and approval from the office of the
City Engineer.
H. The office of the City Engineer shall have final review and approval
authority as to the size and depths required for sanitary sewer mains
and lateral sewers.
4.3.8 Line Depth
A. The sanitary sewer should be laid with the top of the pipe a minimum
of 3 feet below the surface of the natural ground or fmished grade.
B. Sanitary sewers laid in street rights-of-way with a curb and gutter
section shall have a minimum cover of 3 feet from the top of the
pipe to the flowline elevation of the gutter in the street at all
locations. The Professional Engineer of Record shall account for
any anticipated future sanitary sewer extension whereas the future
sanitary sewer extension shall have a minimum 3 feet of cover from
the top of the pipe to the flowline of the gutter of the street. The
Page 10 of 16 Sanitary Sewer Design Cntena
Professional Engineer of Record shall adjust the depth of the
proposed pipe accordingly. The office of the City Engineer reserves
the right to require greater depth where the need is perceived.
C. Sanitary sewers laid in street rights-of-way with crowned roads and
roadside ditches shall have a minimum depth of 6 feet from the
crown of the road to the top of the pipe and an absolute minimum
cover of 2 feet below the flowline of a roadside ditch when non -rigid
pipes of low hoop strength are used. The office of the City Engineer
shall have final determination on any deviation from these criteria.
D. Maximum depth for 8-12 inch diameter collection lines shall be 20
feet from average ground surface to sanitary sewer invert. For
depths greater than 20 feet, Design Engineer shall meet with the
office of the City Engineer to discuss requirements and receive
approval.
4.3.9 Line Grades
A. The following table lists the minimum grade for 6 -inch to 39 -inch
diameter public sanitary sewers. The minimum velocity for a
sanitary sewer flowing full shall be 2.0 feet per second (fps). The
maximum recommended grade shall be calculated by the
Professional Engineer of Record for a maximum velocity of 4.5 fps
based on a Manning equation for full flow with the Manning's "n"
equal to 0.013.
Table 4.1
MINIMUM GRADES FOR SANITARY SEWERS (TCEQ Minimum)
PIPE SIZE
6
8
MINIMUM GRADE (PERCENT)
0.50
0.33
10
12
15
18
21
24
30
36
0.25
0.20
0.15
0.11
0.09
0.08
0.055
0.045
B. For sanitary sewers larger than 36 inches in diameter, the
Professional Engineer of Record shall determine the appropriate
grade utilizing a full pipe maximum velocity of 4.5 fps and
minimum velocity of 2.0 fps.
4.3.10 Gravity sanitary sewer mains shall be laid in straight alignment with
uniform grade between manholes. Grade and alignment changes without
the use of manholes shall not be allowed. .
Page 11 of 16
Sanitary Sewer Design Criteria
4.3.11 Manholes
A. Type: Manholes shall be precast concrete manholes in accordance
with Standard Details and Specifications. No brick manholes shall
be allowed. All manholes shall be coated. Refer to Standard
Specifications for types of coatings. Standard manhole shall have
4' inside diameter. Larger diameter manholes may be required due
to sewer main size, numbers, or configuration at the manhole. It
shall be the responsibility of the Professional Engineer of Record to
ensure that proper diameter manholes is specified. All precast
manholes shall conform to the latest ASTM requirements. Manhole
covers shall be 32" diameter or larger and have the words "Sanitary
Sewer" and the City of Pearland logo cast into the cover per
Standard Detail.. Hinged manholes shall be used in ditch lines and
floodplain areas. All manholes shall be installed with stainless steel
manhole inserts with 1/8 inch vents and strap handles.
B. Location: Manholes shall be placed at changes in alignment,
changes in grade, changes in size of sanitary sewers, at the
intersection of sanitary sewers, junction points, and either at street,
alley, or easement intersections.
a. The maximum distance between manholes shall be
determined from Table 4.2 for 8 inch to 36 inch pipe
diameters. Spacing for manholes on sewer mains with
diameters larger than 36 inches shall be recommended on an
individual basis by the Professional Engineer of Record
subject to City of Pearland approval.
Page 12 of 16
Table 4.2
MAXIMUM DISTANCE BETWEEN
SANITARY SEWER MANHOLES
PIPE DIAMETER ININCHES
8-15
18-36
>36
MANHOLE MAXIMUM SPACING IN FEET 1
400
800
Per Designer of Record, subject to the office of
the City Engineer Approval
c. Place manholes at the dead-end of sewer mains and lateral
sewers. A clean out may be used with prior approval from
the office of City Engineer.
d. Manhole covers shall be cast iron, minimum 32" diameter and
traffic bearing type ring and cover.
e. Criteria for Manhole Junctures
(1) Connections between public sanitary sewers and the
manhole shall adhere to the following criteria.
Sanitary Sewer Design Cnteria
(a) The elevation of the flowline of the
discharging sanitary sewer shall match the
elevation of the flowline of the receiving
sanitary sewer for both equal and unequal
pipe diameters.
(b) Drop manholes in accordance with Standard
Details are allowed. A drop connection or
drop manhole is required when the difference
in elevation between the effluent flowline
and the influent flowline is greater than 36
inches; or where a service line is proposed to
tie onto a sanitary sewer trunk main of 18
inches in diameter or larger.
4.3.12 Manholes should be located as to minimize or eliminate the inflow of
stormwater into the sanitary sewer. The top of manhole rim shall be set a
minimum of 3 inches above the surrounding finished grade when the
manhole is not in a paved roadway. Sealed manholes are required on all
newly constructed manholes within the 100 -year flood plain. Vented
manholes are required a minimum of every 800 feet when not located in the
100 -year floodplain. Unless approved by the office of City Engineer, the
elevation of the top of rim of a sanitary sewer manhole shall be at or above
the be the 100 -year base flood elevation for the area it is being built in. All
manholes above grade shall use Revolution Assembly Rim and Cover. All
manholes in ditches shall have hinged ring and cover.
4.3.13 No cast -in-place manhole is allowed, unless approved by the office of City
Engineer.
4.3.14 Steps in manholes shall not be allowed.
4.3.15 All manhole adjustments shall be made with precast concrete rings when an
additional precast vertical section is too large. No brick shall be used for
manhole adjustments.
4.3.16 All manholes shall be tested by the construction contractor and results
provided to the office of the City Engineer before being accepted by the
City for maintenance. The City reserves the right to require retesting of
manholes if there is reason to question the results. All manhole testing shall
comply with or exceed the procedures and qualifications listed in Texas
Administrative Code, Chapter 217, Section 217.58.
4.3.17 Lift Stations
A. Lift station design and construction drawings as well as design
requirements and pertinent data shall be designed in accordance
Page 13 of 16 Sanitary Sewer Design Cntena
with TCEQ Design Criteria Chapter 217, Sections 217.59 thru
217.63 and sealed by a Professional Engineer registered in the State
of Texas and submitted with the construction drawings for review
by the office of the City Engineer. A preliminary design meeting
with the office of the City Engineer is required. Designer to provide
a master development plan for the service area of the proposed lift
station.
B. Lift Stations should be considered only when a gravity system
cannot be achieved from both an engineering and an economic
standpoint. Lift stations should only be considered with prior
approval from the office of the City Engineer or where the Lift station
is designed to be temporary in nature.
C. Lift station controls shall be enclosed and fenced in such a way to
deter unauthorized operation, vandalism and/or terrorism.
a. Controls and equipment shall be approved by the office of
the City Engineer and in accordance with the Standard
Specifications. Provide dual controls for the wet well.
D. Wet Wells
a. Provide adequate clearance between pumps so as to easily
facilitate retrieval of a pump. Diameter of the wet well,
hatches, and hatch spacing shall be such that to
accommodate the selected pumping equipment. Provide
adequate dimensions for the ultimate pump size and number
in a multi -phase lift station for adequate clearances.
b. Wet well peak flow working volume shall be sized to allow
for the recommended minimum pump cycle time of 10
minutes for each pump for motors 100 hp or less. Use 15
minutes cycle time for motors larger than 100 hp.
c. The invert of a gravity sewer discharge to wet well must be
located above the liquid level of a pump's "on" setting.
d. Wet wells must be enclosed by watertight and gas tight
walls.
e. No gate or check valves shall be located in a wet well.
E. Lift station site — Minimum size of 50 feet by 50 feet. A minimum
12 -feet wide concrete paved, placed above 25 -yr rainfall event
surface, vehicular ingress and egress access to the site shall be
provided. Access road shall be located in a right-of-way or
dedicated easement. The site shall be protected by a lockable
intruder -resistant fence. The Designer shall coordinate with and
receive approval from the office of the City Engineer on type and
height of the fence being placed.
F. The lift station's control panel bottom shall sit a minimum of 3 feet
above the top slab of the lift station wet well .
G. The top of concrete of the lift station's wet well shall sit a minimum
of 2 feet above the nearest base flood elevation.
Page 14 of 16 Sanitary Sewer Design Criteria
H. Pumps shall be sized to operate at optimum efficiency. Minimum
acceptable efficiency at the operating point shall be 60%.
I. Emergency operations should be considered. Provide fittings and a
blind flange that will be readily accessible for emergency bypass
pump.
J. All collection system lift stations shall utilize submersible pumps.
A minimum two (2) pumps shall be required for all lift stations.
Capacity of the pumps shall be such that maximum wet weather flow
can be handled with largest pump out of service.
K. A minimum peaking factor of 4 is required for pump sizing.
L. Provide a summary pump design information such as pump sizes,
TDH, hp, etc. in table format in plans.
M. Unless prior approval is received from the office of the City
Engineer, all stations shall have 480/277 -volt, 3-phase service.
N. Electrical equipment and electrical connections in wet well must
meet National Fire Prevention Association 70 National Electric
Code explosion prevention requirements, unless continuous
ventilation is provided.
0. A geotechnical boring to a minimum depth 15' below bottom of wet
well and a foundation design recommendation is required.
4.3.18 Design Analysis
A. Calculations of design flows for the overall development project
shall be approved by the office of the City Engineer. Peak flow
calculations shall include potential inflow infiltration.
4.4 QUALITY ASSURANCE
4.4.1 Prepare calculations and construction drawings under the supervision of a
Professional Engineer trained and licensed under the disciplines required by
the drawing. The final construction drawings must be sealed, signed, and
dated by the Professional Engineer responsible for the development of the
drawings. If more than one Professional Engineer was responsible for the
development of the design/construction drawings, then the appropriate
Professional Engineer should seal the drawings he/she is responsible for.
4.5 RESIDENTIAL UNSEWERED BUILDING SITES AND SEPTIC TANKS
4.5.1 It is the responsibility of the land owner to file a Citizen Developer Request
(CDR) form with the office of the City Engineer to ensure that a site has
sanitary sewer service available.
4.5.2 For unsewered building sites and building sites with no sanitary sewer
availability, the owner/developer will execute a utility extension agreement
Page 15 of 16 Sanitary Sewer Design Criteria
with the City. The owner/developer must pay for all materials and affect
installation and testing before the City will accept the sewer for
maintenance.
4.5.3 If a lot or parcel is within 200 feet of an existing sanitary sewer then the site
shall tie -on to the existing sanitary sewer. Such building shall comply with
Section 74 Article 3 of the City of Pearland Code of Ordinances.
Page 16 of 16 Sanitary Sewer Design Criteria
CITY OF PEARLAND
CHAPTER 5
STORM SEWER DESIGN CRITERIA
FINAL DRAFT REVSIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 60 Storm Sewer Design Criteria
CHAPTER 5
STORM SEWER DESIGN REQUIREMENTS
5.1 GENERAL
This chapter includes criteria for the design of storm drainage improvements for the City of
Pearland, Texas. These Storm Drainage Design Requirements shall be effective within the
City of Pearland and in the subdivisions located within its extraterritorial jurisdiction. All
drainage work proposed for design within these limits are to adhere to these criteria explicitly.
Any questions regarding their use or function should be addressed to the City Engineer.
5.1.1 Background
Over the years a number of methods have been used in Brazoria County and
adjacent counties for discharge determination in the design and analysis of flood
control facilities. The methods included various forms of the Rational Method,
U.S. Soils and Conservation Society synthetic unit hydrograph analysis using
existing stream gaging records and computer programs developed by the Corps of
Engineers, and U.S. Geological Survey generalized regression equations developed
for the area.
In the mid -1960's, the Harris County Flood Control District (HCFCD) and the City
of Houston commissioned a detailed hydrologic study of Harris County which
resulted in the development of discharge versus drainage area relationships and
unitgraph methodologies used for the design of flood control and drainage facilities.
I n June of 2001, Tropical Storm Allison came ashore on the Upper Texas Coast and
produced record rainfall amounts and pervasive flooding in Hams and surrounding
counties, including the Clear Creek Watershed. In October of 2001, through a joint
effort between FEMA and HCFCD, Harris County began the Tropical Storm
Allison Recovery Project (TSARP). Flood Insurance Studies including for Clear
Creek Watershed were finalized in June 2007.
Special care must be taken to make sure that the correct models and methodologies
are used for projects that require FEMA approval. In any case, for projects
requiring FEMA approval, design engineers should use the current effective model
of the study stream.
In the case that FEMA approval is not required for the project, design engineers
should use the methodology presented in this manual to design drainage facilities
in the City of Pearland.
Page 2 of 60 Storm Sewer Design Criteria
5.1.2 Previous Design Requirements
The criteria of this Manual supersedes the previous document of the same name
dated June 2007. All items listed herein are intended to supersede those documents,
so that all designs of drainage facilities within the City of Pearland, including all
subdivisions within its extra -territorial jurisdiction, shall be based on the criteria of
this Manual from this time forward, until such time as it may be revised or replaced.
5.2 DRAINAGE POLICY
5.2.1 Design Requirements
The drainage criteria administered by the City of Pearland for newly designed areas
provides protection of habitable areas from flooding by large storm events. This is
accomplished with the application of various drainage enhancements such as storm
sewers, roadside ditches, open channels, detention and overland (sheet) runoff. The
combined system is intended to prevent flooding of houses by extreme events up to
the level of a 100 -year storm.
Recognizing that each site has unique differences that can enhance proper drainage,
the intent of these criteria is to specify minimum requirements that can be modified,
provided that the objective for drainage standards is maintained and that such
modifications are made with the approval from the office of the City Engineer.
5.2.2 Street Drainage
Street ponding of short duration is anticipated and designed to contribute to the
overall drainage capability of the system. Storm sewers and roadside ditch conduits
are designed as a balance of convenience and economics. These conduits are
designed to convey less intense, more frequent rainfalls with the intent of allowing
for traffic movement during these events. When rainfall events exceed the capacity
of the storm sewer system, the additional runoff is intended to be stored or conveyed
overland in a manner that reduces the threat of flooding to habitable structures.
5.2.3 Flood Control
The City of Pearland is a participant in the National Flood Insurance Program. The
intent of the flood insurance program is to make insurance available at low cost by
providing for measures that reduce the likelihood of habitable structural flooding.
Fill placed in the 100 -year flood plain as designated on the Flood Insurance Rate
Map below the 100 -year base flood elevation shall be mitigated by removal of like
amount of compensating cut in the vicinity of the fill, while maintaining hydraulic
connectivity to the existing floodplain. All runoff impacts created by development
Page 3 of 60 Storm Sewer Design Criteria
shall be mitigated equal to or less than equivalent pre -project runoff rates and
flooding levels.
5.2.4 Relationship to the Permitting and Platting Process
Approval of storm drainage is a part of the review process for planning and platting
of new development. The review of storm drainage is conducted by the
Engineering Department.
5.2.5 Final Drainage Plan and Plat
A detailed drainage plan for each proposed development shall be prepared by a
Registered Professional Engineer and shall be presented to the City Engineer for
review and approval. The plan shall consist of the detailed design drawings for all
drainage improvements and structures, rainfall runoff, impact data and those notes
to be included as applicable, on the Final Drainage Plan as specified in Sections 5
through 8.
The following items shall be shown on a plan of the development as a minimum:
1. Name, address, phone number, and contact person of engineer that prepared
the plans.
2. Scale of drawing with a minimum scale of 1" = 100'.
3. Benchmark and reference benchmark with year of adjustment.
4. Location or vicinity map drawn to a scale.
5. Date on all submittals with date of all revisions, including month, day, and
year.
6. Contour lines at 0.5 foot intervals or greater with 2 contours minimum
covering the entire development and extended beyond the development
boundaries at least 100 feet on all sides for developments over 5 acres and
50 feet on developments under 5 acres.
7. Lot grading plan, which provides for the passage of sheet flow from
adjacent property.
8. A 100 -year sheet flow analysis that provides direct access to the detention
facility or main outfall.
9. Drainage area divides for project area, with peak run-off rates for each inlet,
structure, or drainage area.
Page 4 of 60 Storm Sewer Design Criteria
10. Locations of pipelines, drainage structures, buildings, or other physical
features on the property and adjacent rights-of-way.
11. True locations of existing creeks, bayous, streams, gullies, and ditches, as
determined by actual ground survey current within one year of approval of
the Preliminary Plan. Show stream alignment 200 feet upstream and 200
feet downstream of development.
12. Cross sections of detention facility, ditches and earthworks.
13. Details of all ditches, which are to convey rainfall runoff from a subdivision
and/or through a subdivision to the appropriate drainage artery and location
of that drainage artery.
14. Drainage easements and dedicated right-of-way along all creeks, bayous,
streams, gullies, and ditches.
15. Bridges which span any creek, bayou, stream, gully, or ditch and specifying
maintenance responsibility and/or ownership of such structures.
16. Culvert type and size shall be shown. No culvert shall be less than 18" in
diameter, without special permission by the City Engineer.
17. Copy of TxDOT permit application if applicable.
18. Copies of letters of approval from entities holding easements or rights-of-
way to be crossed.
19. An erosion control plan acceptable to both the City and the T.C.E.Q. must
be presented with all plans. Copies of all submittals to the T.C.E.Q. shall
be delivered to the City.
20. Seal of a Registered Professional Engineer on all plans and Registered
Public Surveyor or State Licensed Land Surveyor on the plat.
21. The lowest chord of all bridges shall be a minimum 12" above the 100 -year
water surface elevation, or, at or above the level of natural ground, or in
accordance with the FEMA latest regulations, whichever is greater.
5.3 REFERENCES
1. Brazoria Drainage District No. 4, "Rules, Regulations, & Guidelines",
November 5, 1997 (BDD#4 Regulations), amended April 2015.
Page 5 of 60 Storm Sewer Design Criteria
2. Harris County Flood Control District, "Hydrology & Hydraulics Guidance
Manual", December 2009 (HCFCD Criteria).
3. Applicable Portions of the City of Houston Design Manual, Chapter 9, "Storm
Sewer Design Requirements", July 2015.
4. Ordinances of the City of Pearland (as currently amended).
5. U.S. Army Corps of Engineers. HEC -RAS River Analysis System User's
Manual Version 4.1, The Hydrologic Engineering Center, Davis, California,
January 2010.
6. U.S. Weather Bureau. "Rainfall Frequency Atlas for the United Stated for
Durations from 30 Minutes to 24 Hours and Return Periods from 1 to 100
Years," Technical Parser No. 40 January 1963.
7. U.S. Army Corps of Engineers. Civil Works Bulletin 52-8.
8. U.S. Army Corps of Engineers. HEC -HMS Hvdroloeic Modeling System
User's Manual Version 4.0, The Hydrologic Engineering Center, Davis,
California, December 2013.
9. Chow, V. T., Onen-Channel Hydraulics, McGraw-Hill, 1959.
10. Ramser, C. E., Flow of Water in Drainage Channels. U.S. Department of
Agriculture, Technical Bulletin No. 129, November 1929.
11. Engineer Handbook, Hydraulics, Section 5, U. S. Department of Agriculture,
Soil Conservation Service, 1955.
12. Barnes, Harry H., 1967.. Roughness Characteristics of Natural Channels, U. S.
Geological Survey Water Supply Paper, 1849.
13. King, H. W. and E. F. Brater, Handbook of Hydraulics, 6th Edition, McGraw-
Hill, 1976.
14. Research Studies on Stilling Basins, Energy Dissipators, and Associated
Appurtenances, Bureau of Reclamation, Hydraulic Laboratory Report No. Hyd-
399, June 1, 1955.
15. Texas State Department of Highways and Public Transportation standard
specifications for Construction of Highways, Streets, and Bridges latest edition.
16. ASTM A796 Structural Design of Corrugated Steel Pipe, Pipe Arches, and
Arches for Storm and Sanitary Sewers.
Page 6 of 60 Storm Sewer Design Criteria
17. Liscum, F., and B. C. Massey. "Technique for Estimating the Magnitude and
Frequency of Floods in the Houston, Texas, Metropolitan Area," Water
Resources Investigations 80-17, U. S. Geological Survey, April 1980.
18. Federal Emergency Management Agency. Flood Insurance Study - Brazoria
County. Texas and Incorporated Areas, June 5, 1989.
19. Federal Emergency Management Agency. National Flood Insurance Program
and Related Regulations, Index 44 CFR, October 1, 2002.
20. Hare, G. "Effects of Urban Development on Storm Runoff Rates," U. S. Army
Corps of Engineers, Galveston District, September 1970.
21. Malcolm, H. R. A Studv of Detention in Urban Stormwater Management,
Report No. 156, Water Resource Research Institute, University of North
Carolina, Raleigh, North Carolina, July 1980.
22. Texas Water Development Board. "Study of Some Effects of Urbanization on
Storm Runoff from a Small Watershed," Report 23, August 1966.
23. Hydraulic Design of Stilling Basins and Energy Dissioators. Engineering
Monograph No. 25, U. S. Department of the Interior, Bureau of Reclamation,
1964.
24. Viessman, Jr., Warren; John W. Knapp; Gary L. Lewis and Terence Harbaugh,
Introduction to Hvdroloav, Harper & Row, 1977.
25. Coenco, Inc. Master Drainage Plan, April 11, 1980, Revised 1988.
26. Rust Lichliter/Jameson. Flood Protection Plan for Brazoria Drainage District
No. 4, Brazoria County, Texas, November 5, 1997.
27. U.S. Geological Survey, Water Resources Investigations Report 98-4044.
Depth -Duration Freauencv of Precipitation for Texas, Austin, Texas 1998.
28. U.S. Geological Survey & Texas Department of Transportation, Atlas of Depth -
Duration Freauencv of Precipitation Annual Maxima for Texas, June 2004.
29. USACE EM 1110-2-1417.
30. McCuen, Richard H., Prentice Hall, Hydrologic Analysis and Design, 1989.
31. City of Pearland City Ordinance No. 421.
32. City of Pearland City Ordinance No. 532-2.
Page 7 of 60 Storm Sewer Design Criteria
33. City of Pearland City Ordinance No. 817.
34. City of Pearland City Ordinance No. 817-1.
35. City of Pearland City Ordinance No. 669-3.
36. City of Pearland City Ordinance No. 741-3.
37. City of Pearland City Ordinance No. 881.
38. City of Pearland Resolution No. R2003-49
5.4 DEFINITIONS
Backslope Drain
Benchmark
A drain or swale that collects overland peak discharge from
channel overbanks and other areas not draining into the
storm sewer collection system. These may be to prevent
unplanned runoff from entering a detention system, or from
entering a drainage ditch. They are also used to prevent
overland discharge from eroding the sides of a ditch or pond.
A point of known exact elevation, set and used by Surveyors
to start from to obtain elevations on other points of unknown
elevation. The known elevation is usually based on "mean
sea level", and is referenced to a "Year of Adjustment".
BDD#4: Brazoria Drainage District No. 4.
cfs: Cubic Feet Per Second
City Engineer: An Engineer licensed in the State of Texas who is
responsible for reviewing drainage plans or plats under the
authority of and in the employment of the City of Pearland.
CMP:
Coefficient Of Roughness:
Commercial:
Conduit:
Corrugated Metal Pipe
A number used to measure and compare the roughness of
pipe interior or open channel sides and bottom.
Development of real estate for any purpose other than
"residential" as defined herein.
Any open or closed device for conveying flowing water.
Page 8 of 60 Storm Sewer Design Criteria
Construction: The building of a planned or designed project.
Continuity Equation: Q = VA
Where Q = discharge (cfs or cms)
V = velocity (ft/sec or m/sec)
A = cross sectional area of conduit in
square feet or square meters.
Contour Line: A line on a map, chart or plan that follows a continuous line
of a certain known elevation.
Culvert:
One or more pipes that carry the flow of water from one
point in a ditch or channel to another point in a ditch or
channel.
Design Storm Event: The rainfall intensity and/or depth upon which the drainage
facility will be sized.
Detention Control Structure: The outlet pipe or weir, and high-level spillway that limits
the discharge from a detention facility.
Detention Facility: A reservoir, dam, pond or other area where stormwater
collects and is held temporarily. The collected stormwater
is released at a calculated rate through a control structure.
Developer: A person or entity that develops land.
Development:
Development Engineer:
Drainage Area Map:
Drainage Arteries:
A tract of land that has been improved or subdivided,
exclusive of land being used and continuing to be used for
agricultural purposes. Improvement of land includes
grading, paving, building structures, or otherwise changing
the runoff characteristics of the land.
An Engineer licensed in the State of Texas who is
performing work for a Developer.
Area map of watershed which is subdivided to show each
area served by each storm drainage subsystem.
Natural or man-made ditches or channels that intercept and
carry storm water on to a larger major creek, bayou or
stream.
Drainage Plan: An engineering representation of the peak discharge of
rainfall runoff on or onto a particular area, and off of that
Page 9 of 60 Storm Sewer Design Criteria
same area. It may also include systems that will be used to
detain or control runoff and provide flood control for a
development, subdivision, or structure.
Drainage System: A series of swales, storm sewers, ditches and creeks which
function to collect and convey stormwater runoff in a
watershed.
Easement: An area designed and dedicated for a specific use, but
remains the property of the owner out of which it is a part.
The uses may be for drainage, maintenance, access, future
widening of channel or ditch, or other specific uses.
FEMA: The Federal Emergency Management Agency, which
administers the National Flood Insurance Program.
FIRM: Flood Insurance Rate Maps published by a Federal
Emergency Management Agency.
Flood Plain Administrator:
HCFCD:
HDPE:
HEC -HMS:
HEC -RAS:
Hydraulic Analysis:
Hydraulic Grade Linc:
Person identified by the governing municipality or County
as responsible for administering the National Flood
Insurance Program for the City or County in accordance
with guidelines established by FEMA.
Harris County Flood Control District.
High Density Polyethylene
"Hydrologic Modeling System" computer program written
by the U.S. Army Corps of Engineers.
"River Analysis System" computer program written by
U.S. Army Corps of Engineers.
The study and/or definition of the movement of stonnwatcr
through a drainage system.
A line representing the pressure head available at any given
point within the drainage system.
Hydrologic Analysis: The study and/or definition of the properties, distribution
and circulation of stormwater runoff over land or in the soil.
Page 10 of 60 Storm Sewer Design Criteria
Hydromulching: A process that prevents, or helps to prevent erosion of the
soil. When sprayed on an exposed slope, it seals the surface
and seeds it with vegetation.
ICPR: Interconnected Channel and Pond Routing computer
program by Streamline Technologies, Inc. Computes
unsteady gradually varied flow.
Impact: The effect of a proposed development on the hydrology or
hydraulics of a subarea or watershed as defined by an
increase or decrease in peak discharges or water surface
elevations.
Impact Data:
Impervious Cover:
In -Fill Development:
Data required to support the Developer's Engineer to show
the effect the proposed development will have on the
rainfall runoff rates, rainfall concentration times and the
surface level of the affected creek, stream, gully, or ditch
into which proposed development runoff drains.
A land surface cover which does not allow the passage of
stormwater into the underlying soil. Used in hydrologic
analysis to calculate the amount of stormwater runoff from
an area.
Development of open tracts of land in areas where the storm
drainage infrastructure is already in place and takes
advantage of the existing infrastructure as a drainage outlet.
Manning's Equation: V = (Kin) R 2/3 Sf1/2
Metering Device:
Where K = 1.49 for English units,
1.00 for metric units
V = velocity (ft/sec or in/sec)
R = hydraulic radius (ft or m)
(area/wetted perimeter)
Sf = friction slope (headloss/length)
n = 0.013 for concrete pipes,
0.011 for HDPE pipes,
0.028 for CMP
varies for earthen channels
A device or structure containing pipe, V -notch weir, slots
and other configurations designed to measure or regulate
the outflow.
Page 11 of 60 Storm Sewer Design Criteria
Mitigate:
To lessen or eliminate the impact of a proposed
development on the hydrology or hydraulics of a subarea or
watershed.
NA VD North American Vertical Datum or Mean Sea Level,
pertaining to base elevations.
Outfall Structures:
A structure made to contain the outfall pipe or peak
discharge, with necessary weir, slope paving, riprap, or
other methods to control velocity and prevent erosion, and
may contain the metering device.
Outflow: The final peak discharge from the development system into
another or existing drainage system.
Overflow:
Peak Discharge:
The peak discharge that will not pass through the design
pipe or structure, and must go over a weir or some other
relief structure.
The maximum rate of stormwater runoff from a tract of land
or in a ditch or channel, as determined from the maximum
point in cubic feet per second of the calculated hydrograph
for the study area.
Plat: A formal drawing of property lines and spaces that may, or
may not, be recorded.
Rainfall Data: Data pertaining to the amount of rainfall in a certain area
and occurring over a certain specified period of time.
Rainfall Frequency: The probability of a rainfall event of defined characteristics
occurring in any given year. Information on rainfall
frequency is published by the National Weather Service. For
the purpose of storm drainage design, the following
frequencies are applicable:
3-vear freauencv - a rainfall intensity having a 33%
probability of being equaled or exceeded in any given year.
5-vear freauencv - a rainfall intensity having a 20%
probability of being equaled or exceeded in any given year.
10-vear freauencv - a rainfall intensity having a 10%
probability of being equaled or exceeded in any given year.
Page 12 of 60 Storm Sewer Design Criteria
25 -year frequency - a rainlall intensity having a 4%
probability of being equaled or exceeded in any given.
100-vear frequency - a rainfall intensity having a 1%
probability of being equaled or exceeded in any given year.
Rainfall Runoff: The portion of the precipitation on the land that ultimately
reaches the drainage system.
Rational Formula: A method for calculating the peak runoff for a storm
drainage system.
Redevelopment: A change in land use that alters the impervious cover from
one type of development to either the same type or another
type, and takes advantage of the existing infrastructure in
place as a drainage outlet.
RCP:
Regional Detention Facility:
Residential:
Right Of Way:
Runoff
Runoff Coefficient:
Sheet Flow:
Site:
Reinforced Concrete Pipe.
A detention facility that collects and holds stormwater from
more than one development or from one of the major creeks
or tributaries in the City of Pearland.
Of or pertaining to single family detached dwelling(s) not
including multi -family townhomes, condominium,
duplexes, or apartments.
A strip of land that is set aside and reserved for certain
purposes including drainage and maintenance, and possibly
future widening of a drainage channel.
That part of rainfall on property that does not soak in or
evaporate, and ultimately reaches drainage arteries.
A comparative measure of different soils, slopes and
growths, and improvements, for their capability of allowing
the peak discharge of water to move along and over them.
Overland storm runoff that is not conveyed in a defined
conduit, and is typically in excess of the capacity of the
conduit.
A space of ground occupied or to be occupied by a building
or development.
Page 13 of 60 Storm Sewer Design Criteria
Spillway:
Subdivide:
Subdivision:
Siva/e:
TSARP:
The part of the outfall structure that allows and controls the
"overflow" that does not go through the structure.
To divide a tract of land into two or more smaller tracts or
building lots.
A tract of land which has been separated from surrounding
tracts and has been divided into two or more lots.
A very shallow ditch that usually has very long sloping
sides, in some cases not much more that a small depression
that allows water to peak discharge in a somewhat
controlled manner.
Tropical Storm Allison Recovery Project. Federally funded
flood study managed by Harris County Flood Control
District begun in October of 2001.
U.S. G.S. SIR 2004-5041 2004 U.S.G.S Publication regarding rainfall depth -duration
frequency relationships for Texas
Variance:
Watershed:
A one time formal exception to a particular rule or rules
granted for extenuating circumstances, by a City Council
resolution.
A region or area bounded peripherally by a ridge of higher
elevation and draining ultimately to a particular
watercourse or body of water.
5.5 STORM SEWER AND ROAD -SIDE DITCH DESIGN REQUIREMENTS
Storm sewer structures shall be per City of Pearland Standard Details. Additionally, unless
otherwise noted, the City of Pearland also adopts the hardware requirements of the City of
Houston Standard Specifications and Standard Drawings. Manhole covers shall include
the City of Pearland designation as shown in Standard Details. Grates, etc. shall have
generic designation.
Furthermore, all outfall pipes, ditches, and structures that enter District Channels shall also
be designed in accordance with BDD#4 Regulations or HCFCD Criteria. In such instances
wherein a conflict of these criteria arises, the most stringent requirements of these shall be
utilized for the design.
To distinguish the adequacy of road -side ditches to be designed by the following
requirements of this section, it is important to note that these ditches DO NOT include
channels which receive runoff flows from any other outfall drainage sources other than
Page 14 of 60 Storm Sewer Design Criteria
direct overland runoff flows. Design of channels that do receive outfall system drainage
can be found in Section 5.7.0 of this Manual.
5.5.1 Determination of Runoff
The quantity of storm water runoff (peak discharge) shall be determined for each inlet,
pipe, roadside ditch, channel, bridge, culvert, outfall, or other designated design point by
using the following standards applicable to the above requirements.
A. Application of Runoff Calculation Models
a. Acceptable Methodology For Areas Less Than 200 Acres
For areas up to 200 acres served by storm sewer or roadside ditch, peak
discharges will be based on the Rational Method. If the modeling is
associated with establishing a flood -prone area for purposes of a FEMA
submittal, the models to be used must be acceptable to that agency.
b. Acceptable Methodology For Areas Greater Than 200 Acres
Rainfall runoff modeling will be applied to areas greater than 200 acres
in size. Again, if the modeling is associated with establishing a flood -
prone area for purposes of a FEMA submittal, the models to be used
must be acceptable to that agency.
B. Rainfall Durations for Hydrologic Modeling
For design using the HEC -HMS model, the 24-hour design storm
isohyetograph will be used for rainfall data for drainage areas larger than
200 acres.
C. Application of the Rational Method
Use of the Rational Method for calculating the peak runoff for a storm
drainage system involves applying the following formula to runoff:
Q = CIA
Where Q = peak discharge (cfs)
C = watershed coefficient
A = area in acres
I = rainfall intensity (inches per hour)
a. Calculation of Runoff Coefficient
Page 15 of 60 Storm Sewer Design Criteria
The runoff coefficient "C" values in the Rational Method formula will
vary based on the land use. Land use types and "C" values which can be
used are as follows:
Land Use Tyne Runoff Coefficient*
Paved Areas/Roofs** 1.0
Residential Districts
Lots more than 1/2 acre 0.40
Lots 1/4 - 1/2 acre 0.50
Lots 8,000 sf. —1/4 acre 0.55
Lots 5,000 sf. — 8,000 sf. 0.60
Lots less than 5,000 sf. 0.70
Multi -Family areas
Less than 20 DU/AC
20 DU/AC or Greater
Business Districts
Industrial Districts
Railroad Yard Areas
Parks/Open Areas
Rice Fields/Pastures
Lakes/Detention Ponds***
Dry Detention Ponds
0.75
0.85
0.95
0.95
0.30
0.30
0.20
1.0
0.85
*When calculating "C" values for proposed developed areas, multiply listed
values by 1.05 to reflect saturated conditions.
**Includes concrete, asphalt, gravel, limestone, crushed stone, and lime
stabilized surfaces.
***Includes wet detention facilities. Area will be computed from top of
slope.
Composite "C" values for mixed-use drainage areas are allowed for use in
the Rational Formula. These values are to be obtained by calculating a
weighted average of all the different "C" values of the sub -areas
contributing to each mixed-use drainage area. Any calculations of these
Composite "C" values are to be provided as part of the drainage
calculations.
C =j1At + C2A2+C3A3 ..�
(A1+Az+A3 ...An)
The calculations and an exhibit of surface types for use of composite "C"
values shall be included with the drainage calculations and provided in
plans.
b. Determination of Time of Concentration
Page 16 of 60 Storm Sewer Design Criteria
The following method shall be used for determining the time of
concentration:
Tc = D/(60*v) + Ti
Where Tc = Time of concentration (minutes)
Ti = Initial time (minutes)
Use 10 minutes for developed flows
Use 15 minutes for undeveloped flows
D = Travel distance on flow path (feet)
V = Velocity (ft/sec)
The time of concentration shall be calculated for all inlets and pipe
junctions in a proposed storm drainage system or other points of runoff
entry to the system. Time of concentration shall be based upon the
actual travel time from most remote point in the drainage area to the
point of runoff. The design engineer shall provide a sketch of the travel
path with the computations.
The following minimum and maximum velocities shall be used when
calculating the time of concentration:
SURFACE
TYPE
storm sewer
ditch / channel
paved area
bare ground
grass
vegetation
UNDEVELOPED
FLOWS MIN V (fps)
3.00
2.00
1.50
0.50
0.35
0.25
DEVELOPED
FLOWS MIN V (fps)
3.00
2.50
1.50
1.00
0.50
0.35
For storm sewers, time of concentration for other analysis points
shall be the highest time of concentration of the previous upstream
contributing area(s) plus time of flow in the pipe. For drainage areas
of one acre or less the time of concentration need not be calculated
and a storm duration of 10 minutes for mostly impervious area or 15
minutes for mostly pervious area may be used as the basis of design.
Page 17 of 60 Storm Sewer Design Criteria
c. Rainfall Intensity
The time of concentration of the runoff will be used to determine the
rainfall intensity component of the Rational Method Formula. The
rainfall intensity shall be computed as follows:
I = b/(Tc +d)^ e
COEFFICIENT
TT<=60 min
b
d
e
Where I = Rainfall intensity (in/hr)
Tc = Time of Concentration (min)
B, d, e = Coefficient pert table below
100 -YEAR 50 -YEAR 25 -YEAR 1 10 -YEAR 5 -YEAR 1 3 -YEAR
90.8 107.0
16.5 21.1
0.685 0.734
98.5 107.9
24.0 23.6
0.729 0.781
"I,:>60 min
b 84.0 86.5 89.2
d 11.0 10.0 10.4
92.9
19.7
0.788
96.6 70.1
17.2 7.7
c 0.679 0.709 0.736
d. Sample Calculation Forms
0.770 0.752
90.6
19.5
0.803
710
8.4
0.774
Figure 5.5-1 represents a sample calculation form for storm sewer
systems.
Page 18 of 60 Storm Sewer Design Criteria
b
rdOo FIGURE 5.5-1: STORM SEWER CALCULATION TABLE
sp CITY OF PEARLAND
0 STORM FREQUENCY: XX - YR
Project:
By:
Date:
Node Area Total Area Time of
From To (AC) (AC) C Factor Conc. (TC)
Storm Sewer Design C.iteria
Rainfall Flow Q Reach Line Flow Line Design Actual HGL Sic, . HGL TOC RIM HGL - TOC
Intenstity (CFS) (FT) Size (IN) Mann U/S (FT) D/S (FT) V (FPS) Flow Q Velocity (%) U/S (FT) D/S (FT) U/S (FT) D/S) (FT) U/S (FT) D/S (FT)
(IN/HR) Const (n) (CFS) (FPS)
5.5.2 Design of Storm Sewers
A. Design. Frequency
a. Newly Developed Areas
The design storm event for sizing storm sewers will be a 3 -year rainfall.
The storm sewer should be designed so that the design hydraulic grade
line shall be at or below the curb gutter grade for a curb and gutter
section, and six inches below the shoulder of a roadside ditch section.
For major thoroughfares, the design storm event will be a 5 -year rainfall.
b. Redevelopment or In -fill Development
The existing storm drainage system will be evaluated using a 3 -year
rainfall, assuming no development takes place. The same system will
then be evaluated with the development in place. Modifications to the
existing drainage system are to be considered based on the following:
1) If the proposed redevelopment has a lower or equal runoff
potential, no modifications to the existing storm drainage system are
required.
2) If the hydraulic gradient of the affected existing storm drainage
system is below the curb gutter grade (or six inches below the
shoulder of a roadside ditch section), no improvements to the
existing storm drain are required.
3) If the hydraulic gradient is above the gutter grade (or the edge of
shoulder of a roadside ditch section), the drainage system must be
analyzed for the impact of the 100 -year storm event. If the 100 -year
event is at or below one foot below the floor levels of adjacent
existing habitable structures, and exceeds the top of curb (or the
centerline elevation in a roadside ditch section) by twelve inches or
less, no improvements to the existing system are required.
If none of these conditions are met by the proposed development
changes, improvements to the existing system will be required.
In all cases of improved development (development which increases
the runoff potential of the site), mitigation in the form of onsite or
offsite detention must be either purchased or provided. Alternatives for
mitigation detention are referred to elsewhere in these Criteria.
Page 20 of 60 Storm Sewer Design Criteria
c. City of Pearland Projects (Capital Improvement Programs)
Proposed City of Pearland Capital Improvements Program may indicate
that a larger diameter storm sewer is planned in the area proposed for
drainage improvements. The City Engineer will provide information on
planned capital improvements and should be consulted as to its impact
on new development.
d. Private Drainage Systems
Drainage facilities draining private areas shall be designed in
conformance with appropriate design standards. The City of Pearland
will not approve nor accept for maintenance a drainage system on
private property unless it drains public water and is located in a drainage
easement. The connection of any storm sewer, inlet, or culvert to a
public drainage facility will be approved by the City of Pearland. Storm
water shall not be discharged or flow over any public sidewalk or
adjoining property except to existing creeks, ditches, streets, or storm
sewers in public rights of way or easements. Drainage to an existing
Texas Department of Transportation (TxDOT) ditch, road, or storm
sewer, must be approved or documented with a permit, letter or note of
no objections by TxDOT to the plan.
B. Velocity Considerations
a. Minimum velocities should not be less than 3 feet per second with the
pipe flowing full, under the design conditions.
b. Maximum velocities should not exceed 8 feet per second without use of
energy dissipation before release to natural or cultivated grass channels.
C. Pipe Sizes and Placement
a. Use storm sewer and inlet leads with at least 18 -inch inside diameter or
equivalent cross section. Box culverts shall be at least 2' x 2'. Closed
conduits (circular, elliptical, or box) shall be selected based on hydraulic
principals and economy of size and shape. For inlets and leads carrying
5 cfs or more, 24 -inch inside diameter is the minimum.
b. Larger pipes upstream should not flow into smaller pipes downstream
unless construction constraints prohibit the use of a larger pipe
downstream, or the improvements are outfalling into an existing system,
or the upstream system is intended for use in detention.
Page 21 of 60 Storm Sewer Design Criteria
c. Match crowns of pipe at any size change unless depth constraints or
other conditions justify matching flow lines.
d. Locate storm sewers in public street rights-of-way or in approved
easements of adequate width. Back lot and side lot easements are
discouraged and must be justified.
e. Follow the alignment of the right-of-way or easement when designing
cast in place concrete storm sewers.
f. A straight line shall be used for inlet leads and storm sewers.
g. Center all culverts <48" within storm sewer easements wherever
possible.
h. Cast -in-place concrete storm sewers require prior approval from the
office of the City Engineer.
D. Starting Water Surface and Hydraulic Gradient
a. The hydraulic gradient shall be calculated assuming the top of the outfall
pipe as the starting water surface elevation when the total time of
concentration for the project drainage system is less than 30% of the
time of concentration of its outfall waterway. When the total time of
concentration for the project drainage system is greater than 30% of the
time of concentration for its outfall waterway, a comparison between
the 3 -year water surface elevation of the receiving stream and the soffit
of the outfall pipe must be made. In that instance, whichever value is
higher shall be used as the starting tailwater condition.
b. At drops in pipe invert, should the upstream pipe be higher than the
hydraulic grade line, then the hydraulic grade line shall be recalculated
at a value of 80% of the upstream pipe diameter above the downstream
flowline of the upstream pipe.
c. For the 3 -year design storm, the water surface elevation shall at all times
be below the gutter line for all newly developed areas. In major
thoroughfares, the 5 -year storm water surface elevation shall be below
the gutter line.
E. Manhole Locations
a. Use manholes for precast conduits at the following locations:
(1) Size or cross section changes.
(2) Inlet lead and conduit intersections.
(3) Changes in pipe grade.
Page 22 of 60 Storm Sewer Design Criteria
(4) Street intersections.
(5) A maximum spacing of 600 feet measured along the conduit
run.
(6) Manholes and inlets shall not be located in driveway areas.
b. Use manholes for monolithic -concrete storm sewers at the same
locations as above with the permitted exception at intersections of inlet
leads unless needed to provide maintenance access.
F. Inlets
a. Locate inlets at all low points in gutter.
b. Valley gutters across intersections are not permitted without approval
from the City Engineer.
c. Inlet spacing is a function of gutter slope , contributing drainage area,
and ponding width and height. Inlet spacing should be designed to
conform with 5.3.3 b and c. For minimum gutter slopes, the maximum
spacing of inlets shall result in a gutter run of 350 feet from high point
in pavement, with a maximum total of 700 feet of pavement draining
towards any one inlet.
d. Use the following standard inlets as detailed in standard details:
Inlet Application Capacity
Type A Parking Lots/Small Areas 2.5 cfs
Type B -B Residential/Commercial 5.0 cfs
Type C Residential/Commercial 5.0 cfs
Type D Parking Lots 2.0 cfs
Type D-1 Small Areas 2.5 cfs
Type E Roadside Ditches 20.0 cfs
e. Do not use "Beehive" grate inlets or other "specialty" inlets without
approval from City Engineer.
f. Do not use grate top inlets in unlined roadside ditches.
g. Place inlets at the end of proposed pavement, if drainage will enter or
leave pavement.
h. Do not locate inlets adjacent to esplanade openings.
i. Place inlets on side streets intersecting major streets, unless special
conditions warrant otherwise.
j. For lots 65' in width or greater, place inlets at mid lot.
Page 23 of 60 Storm Sewer Design Criteria
G. Outfalls
Storm sewer and open street ditch outfalls to Brazoria Drainage District No
4 or Harris County Flood Control District ditches shall be per BDD#4 or
HCFCD criteria, as approved by the District and City Engineer.
5.5.3 Consideration of Overland Flow
All storm drainage designs will take into consideration the overland flow of runoff
to account for the possibility of system inundation, obstruction, failure, or events
that exceed the design storm. A representation of the overland flow scheme must
be submitted with the system design.
A. Design Frequency
The design frequency for consideration of overland sheet flow will focus on
extreme storm events which exceed the capacity of the underground storm
sewer system resulting in ponding and overland sheet flow through the
development to the primary outlet or detention basin. Unless otherwise
accepted by the City Engineer, the default storm event for this type of
analysis is the 100 -year storm.
B. Relationship of Structures to Street
All structures will be 12 inches higher than the highest level of ponding
anticipated resulting from the extreme event analysis. All finish floor levels
of habitable structures shall be in accordance with the City's Flood Damage
Prevention Ordinance.
C. Calculation of Flow
a. Streets will be designed so that consecutive high points in the street will
provide for a gravity flow of sheet flow drainage to the ultimate outlet.
b. The maximum depth of ponding of the 100 -year event allowed will be
9 -inches above the top of curb for minor collector and local streets, and
3 -inches above top of curb for major and secondary thoroughfare roads.
c. Sheet flow between lots will be provided only through a defined
drainage easement, through a separate instrument, or on the plat.
d. A map shall be provided to delineate extreme event flow direction
through a proposed development and how this flow is discharged to the
primary drainage outlet or detention basin.
Page 24 of 60 Storm Sewer Design Criteria
e. In areas where ponding occurs and no sheet flow path exists, then a
calculation showing that runoff from the 100 -year event can be
conveyed (or stored) and remain in compliance with the other terms of
this paragraph must be provided.
5.5.4 Design of Roadside Ditches
Open ditch subdivisions and asphalt streets are prohibited unless in an area
conforming with "RE" zoning as specified in the City's Land Use and Urban
Development Ordinance or unless a variance has been granted by the City. In either
of these exceptions, the following shall apply to the design of roadside ditches
A. Design Frequency
a. The design storm event for the roadside ditches shall be a 3 -year rainfall.
b. The 3 -year storm design capacity water surface elevations for a roadside
ditch shall be no higher than six inches below the edge of shoulder or
the natural ground at the right of way line, whichever is lower.
c. The design must include an extreme event analysis to indicate that
habitable structures will not be flooded.
B. Velocity Considerations
a. For grass lined sections, the maximum design velocity shall be 3.0 feet
per second during the design event.
b. A grass lined or unimproved roadside ditch shall have side slopes no
steeper than three horizontal to one vertical.
c. Minimum grades for roadside ditches shall be 0.1 foot per 100 feet
(0.1 %) unless approved by the City Engineer.
d. Calculation of velocity will use a Manning's roughness coefficient of
0.035 for improved earthen sections and 0.025 for ditches with paved
inverts.
e. Use erosion control methods acceptable to the City of Pearland when
design velocities are expected to be greater than 3 feet per second.
C. Culverts
a. Culverts will be placed at all driveway and roadway crossings, and
other locations where appropriate.
Page 25 of 60 Storm Sewer Design Criteria
b. Culverts may not be extended across property frontage to cover the
roadside ditch except for driveways.
c. Culverts will be designed assuming either inlet control or outlet
control, whichever the situation dictates.
d. Roadside culverts are to be sized based on drainage area. Calculations
are to be provided for each block based on drainage calculations. Head
losses in culverts shall conform to TxDOT Hydraulics Manual.
e. Cross open channels with roadside culverts no smaller than 18 inches
inside diameter or equivalent. The size of culvert used shall not create
a head loss of more than 0.20 feet greater than the normal water surface
profile without the culvert.
f. Storm water discharging from a ditch into a storm sewer system must
be received by use of an appropriate structure (i.e., stubs with ring
grates or type "E" inlet manholes).
D. Depth and Size Limitations for Roadside Ditches
The use of roadside ditch drainage systems is stipulated by other City
development codes. When the use of open ditch drainage systems is
approved, the following shall apply to the design of roadside ditches:
a. Roadside ditches shall drain streets and adjacent land areas.
b. Residential Streets - The maximum depth of proposed roadside ditches
will not exceed 4 feet from centerline of pavement.
c. Commercial and Thoroughfare Areas - The maximum depth of
proposed roadside ditches will not exceed 4 feet.
d. Roadside ditch bottoms should be at least 2 feet wide, unless design
analysis will support a narrower width.
e. Roadside ditch in slopes shall be set at a ratio of 3:1 or flatter.
f. Ditches in adjoining and parallel easements shall have the top of bank
not less than 2 feet from the outside easement line.
g.
The minimum street right-of-way for open ditch drainage in residential
developments shall be 80 feet in width. Rights-of-way shall be wider
for deep ditches. The minimum open -ditch section roadway shall be
24 ft. pavement with 6 ft. shoulders on each side.
Page 26 of 60 Storm Sewer Design Criteria
5.5.5 Design of Outfall Pipes
Outfall design shall conform to BDD#4 rules or HCFCD Criteria, as appropriate,
and as approved by the City Engineer and the Drainage District. Section 5.6.0 of
this Manual generally incorporates these two counties' rules and/or criteria and
shall apply to all channel and detention designs subject to their requirements.
Pipe discharges of stormwater into earthen channels shall not exceed 5 feet per
second.
5.5.6 Storm Water Mitigation Detention Altematives
Detention basin design shall conform to City of Pearland criteria, BDD#4 rules, or
HCFCD criteria on a case-by-case basis as approved by the office of City Engineer.
The City of Pearland detention design criteria appear in Section 5.8 of this Manual.
5.6.0 HYDROLOGIC ANALYSIS OVERVIEW
The selection of an appropriate hydrologic methodology for all projects shall be carried out
m accordance with Figure 5.6-1. The design engineer should contact the appropriate
reviewing agencies prior to preparing his analysis to obtain approval of the selected
methodology. Regardless of the results of the methodology selected, the minimum
detention required for all projects shall be 0.65 acre feet per acre in addition to
floodplain fill mitigation.
HEC -HMS was created at the U.S. Army Corps of Engineers (USACE) Hydrologic
Engineering Center (HEC). Please note that a rainfall runoff analysis using HEC -HMS
should only be used in cases where it is required for FEMA submittals or where a reviewing
agency has determined that the design engineer must investigate the downstream impacts
of the proposed project. In any case, for projects requiring FEMA approval, design
engineers should use the most current effective model of the study stream.
5.6.1 Peak Discharge Determination
For areas draining less than 200 acres, the natural, existing and proposed discharge
rates can be determined by the Engineer using the Rational Method Formula,
Q = CIA, where C is the runoff coefficient, I is the rainfall intensity, and A is the
drainage area. See Section 5.1.3 of this manual for the application of this method.
5.6.2 Small Watershed Method Hydrograph Methodology
The small watershed method referred to is the one developed by H.R. Malcolm and
is described below.
A. Introduction
Page 27 of 60 Storm Sewer Design Criteria
A technique for hydrograph development which is useful in the design of
detention facilities serving relatively small watersheds has been presented
by H.R. Malcolm. The methodology utilizes a pattern hydrograph which
peaks at the design flow rate and which contains a runoffvolume consistent
with the design rainfall. The pattern hydrograph is a two-part function
approximation to the dimensionless hydrograph proposed by the Bureau of
Reclamation and the Soil Conservation Service.
B. Equations
The Small Watershed Hydrograph Method consists of the following
equations:
Tp = V (1)
1.39Qp
Qp 7t t,
q, = 2 1— co. )]
Tp
-I 30t,
q,=4.34Q,,e Tp
for t, < 1.25 Tp (2)
fort, > 1.25Tp (3)
* Calculator must be in radian mode.
where Tp is the time (in seconds) to Qp, Qp is the peak design flow rate (in
cubic feet per second) for the subject drainage area, V is the total volume of
runoff (in cubic feet) for the design storm, and t; and q, are the respective
time (s) and flow rates (cfs) which determine the shape of the inflow
hydrograph. All variables must be in consistent units.
C. Applications
The peak flow rate, Qp, is obtained from the Rational Method Formula. For
detention mitigation analyses the Rational Method should be applied in
accordance with Section 5.1.3 of this manual, with the exception that all
proposed developed runoff coefficients (C) given in that section should be
inflated by 5%. The total volume of runoff (V) is the same as the rainfall
excess. Table 5.6-1 below gives typical values for the rainfall excess based
on percent impervious cover. The actual values may be interpolated from
the table. See Table 5.6-3, Section 5.6.3.3, for determination of percent
impervious cover.
Page 28 of 60 Storm Sewer Design Criteria
Table 5.6-1. Typical Rainfall Excess Values
To Be Used with Small Watershed Method
100 -Year 10 -Year 3 -Year
Impervious Cover Rainfall Excess (in.) Rainfall Excess (in) Rainfall Excess (in)
100% 135 8.3 6.1
90% 13.2 8.0 5.7
80% 13.0 7.8 5.4
70% 12.7 7.5 5.2
60% 12.4 7.3 5.0
50% 12.2 7.0 4.8
45% 12.0 6.9 4.7
40% 1 1.9 6 8 4.6
35% 1 I.8 6.7 4.5
30% 1 1.6 6.6 4.4
20% 1 1.4 6.3 4.2
10% 11.1 6.1 4.0
0% 10.8 5.9 3.8
The Small Watershed Hydrograph Method should only be used where an
impact analysis is not required for the total drainage system including the
detention facility and outfall channel (as indicated in Figure 5.6-1). The
Small Watershed Hydrograph Method cannot be used in conjunction with
the HEC -HMS models of watersheds studied in the Flood Insurance Study.
The time to peak of the Small Watershed Hydrograph Method is computed
strictly to match volumes and has no relationship to the storm durations and
rainfall distributions used in the Flood Insurance Study.
5.6.3 Watershed Modeling
In October of 2001, through a joint effort between FEMA and HCFCD, Harris
County began the Tropical Storm Allison Recovery Project (TSARP). TSARP
models for Clear Creek simulated the existing conditions in Clear Creek Watershed
when released in June 2007. The effective models for Clear Creek watershed can
be downloaded from the HCFCD Model and Map Management website at
www.m3models.org. Design engineers should always use the current effective
model when FEMA approval is required.
In the case that FEMA approval is not required for the project, design engineers
should use the methodology presented in this Chapter to design drainage facilities
in the City of Pearland.
A. Rainfall Frequency and Duration
The storm event used to establish regulatory flood plain and floodway limits
in the Flood Insurance Study is the 100 -year, 24-hour event. For planning
purposes and establishing flood insurance rate zones the 10-, 50-, and 500 -
year events also require analysis. For projects requiring FEMA submittals,
Page 29 of 60 Storm Sewer Design Criteria
ro
ra
oa
ro0
0
0
City of Pearland
Figure 5.6-1. Hvdrolonic Method Determination - Mitiaation Analysis
Hydrologic Method
Determination - Mitigation Analysis
Storm Sewer Design Criteria
11
I
un
Methodology
Must be Acceptable
to FEMA
Methodology
Must be Acceptable
to Reviewing Agency
Inquire About
Eligibility for
Purchasing Regional
Detention
Use 0.65 ac-tt
Per Ac. Size Outlet
Per Section 8.3.2.
1
4111010.
�� :.3I.
Use Small
Watershed Method
Use Appendix A
Methodology
the rainfall depths in the most current effective model should be used. For
all other projects requiring a rainfall runoff analysis, the depths should be
based on Table 5.6-2, which includes the maximum values for each depth,
duration and frequency from the TSARP, TP40 and Hydro 35 information.
Point rainfall amounts for various durations and frequencies for use in the
City are given in Table 5.6-2.
Table 5.6-2. Point Rainfall Depth (Inches) Duration -
Frequency Values1
Depth (in)
_ 100- 25- 10- a 5- 3 -
Duration Year Year Year Year Year
5 min. 1.20 1.00 0.90 0.80 0.70
30 min. 3.00 2.4 2.10 1.90 1.60
1 hr. 4.3 3.4 2.90 2.50 2.20
2 hr. 5.7 4.4 3.70 3.10 2.60
3 hr. 6.8 5.1 4.20 3.50 2.80
6 hr. 9.10 6.6 5.30 4.40 3.30
12 hr. 11.10 8.00 6.40 5.30 4.00
1 24 hr. 1 13.50 9.80 7.80 _ 6.40 4.80
B. Rainfall Depth -Area Relationship and Temporal Distribution
The version of HEC -HMS that was available at the time of the TSARP does
not have an option for depth -area indices for watersheds larger than 10
square miles. Therefore, it was decided to use point rainfall depths to
specify the hypothetical rain events used in the hydrologic analyses. For
projects requiring FEMA approval, the rainfall input of the most current
effective model should be used. For projects not requiring FEMA
submittals, point rainfall depths should be used.
The version of HEC -HMS that was available at the time of the TSARP
allows the user to shift the peak of the storm from 50% of the storm duration
to 25%, 33%, 67%, or 75% of the storm duration. For projects requiring
FEMA approval, the rainfall input of the current effective model should be
used. For projects not requiring FEMA submittals, the 67% duration
peaking temporal rainfall distribution should be used see Exhibit 6-1.
C. Loss Rates
' Source. TP -40, Hydro -35 and USG S
Page 31 of 60 Storm Sewer Design Criteria
Rainfall excess and runoff volume are dependent on factors such as rainfall
volume, rainfall intensity, antecedent soil moisture, impervious cover,
depression storage, interception, infiltration, and evaporation. The extent
of impervious cover and depression storage is actually a measure of
development and is discussed in the next section. The other factors are
dependent on soil type, land use, vegetative cover, topography, time of year,
temperature, etc.
For projects requiring FEMA approval, the loss input in the most current
effective model should be used. For all other projects requiring a rainfall
runoff analysis, the Green-Ampt loss function available in HEC -HMS shall
be used. A detailed description of the the Green-Ampt loss function can be
found in USACE EM 1110-2-1417. The following parameters should be
used to compute the Green-Ampt losses:
Initial Loss = 0.1 inches
Volume Moisture Deficit = 0.385
Wetting Front Suction = 12.45 inches
Hydraulic Conductivity = 0.024 in/hr
Additional development in the watershed is analyzed by increasing the
value of the impervious cover parameter in the runoff model. Table 5.6-3
gives appropriate values of percent impervious based on land use types:
Table 5.6-3. Percent Impervious Cover For Land Use Types
Land Use % Impervious
High Density 85%
Dry Detention Ponds 85%
Undeveloped 0%
Developed Green Areas 15%
Residential Small Lot
(<1/4 acre or schools) 40%
Residential Large Lot
(>1/4 acre or older neighborhoods with
limited roadside ditch capacity) 20%
Residential Rural Lot
(>_5 acre ranch or farm) 5%
Isolated Transportation 90%
Water 100%
Light Industrial 60%
Airport 50%
Page 32 of 60 Storm Sewer Design Criteria
5.6.4 Unit Hydrograph Methodology
The model that the Clear Creek Watershed flood insurance study is based on the
Clark unit hydrograph. In cases where FEMA submittals are required, the design
engineer should use the Clark unit hydrograph method. In other cases, where a
downstream impact analysis is required, consult the appropriate reviewing agencies
on the applicability of the Clark unit hydrograph. In some cases, other unit
hydrograph methods may be applicable.
The watershed parameters for the Clark unit hydrograph may be developed using
the Harris County methodology. Design engineers should refer to the current
effective model available on HCFCD Model and Map Management Website (http://
http://www.m3models.org/) and the most recent version of the HCFCD hydrology
manual.
5.6.5 Flood Hydrograph Routing
Flood routing is used to simulate the runoff hydrograph movement through a
channel or reservoir system. Flood routing techniques vary greatly between
hydrologic computer models and caution should be used in selecting a routing
method, which adequately represents the channel storage conditions present in
areas with extremely flat slopes, such as within the City of Pearland.
The HEC -HMS program employs several flood routing methods for characterizing
the transfer of the runoff hydrograph through the drainage system of a watershed.
The models developed for the Flood Insurance Study for the Clear Creek watershed
use the Modified Puls Method of routing. This flood routing method is based on
the continuity equation and a relationship between flow and storage or stage. The
routing is modeled on an independent -reach basis from upstream to downstream.
A detailed discussion of the Modified Puls Method can be found in the user's
manual for HEC -HMS.
A. Storage —Routing Computations Using HEC -RAS
All of the Flood Insurance Study data submitted for the Clear Creek
Watershed have utilized the HEC -RAS computer program to generate the
storage -discharge relationship required for HEC -HMS to utilize the
Modified Puls flood routing. Listed below is a suggested procedure by
which the HEC -RAS program can best be formatted to provide the most
effective input and output data necessary for hydrologic studies.
a. Determine which routing reaches of the subject channel will need to be
evaluated. Routing reaches that are defined in the Flood Insurance
Page 33 of 60 Storm Sewer Design Criteria
Study usually represent an area between outfalls of two significant
drainage areas.
b. Review all the available data for the routing reaches of the subject
stream.
c. Run HEC -HMS for the 100 -year storm event using preliminary channel
routing data or alternate methods (i.e. Muskingum or Lag).
d. Use the effective model to determine the 100 -year flows for the stream
in question. Multiply the preliminary 100 -year peak discharges
determined above by 0.20, 0.40, 0.60, 0.80, 1.00, 1.20, and 1.50 to
obtain a series of seven discharges for each storage routing reach.
e. The discharges that have been developed are then input to the HEC -
RAS program. The discharges should be held constant throughout the
subject routing reach. Outflows through a routing reach should not vary.
f. Obtain storage outflow data calculated using HEC -RAS utilizing the
most upstream and downstream cross section of the reach.
g.
Determine the average flood wave travel time along the reach. To
calculate the average wave travel time, divide reach travel time by a
flood wave velocity factor of 1.5.
h. Determine the number of subreaches to be used in the HEC -HMS
computations. Determine this number by dividing the average flood
wave travel time along the reach by the HEC -HMS computational time
step for each of the flows entered in the HEC -RAS model.
i. Run the HEC -HMS model.
j. Cycle (or balance) the HEC -HMS and HEC -RAS until the 1%
exceedance probability (100 -year) flows at the downstream end of the
routing reach match within 5%.
The HEC -RAS model used in the storage -outflow analysis should be
reviewed to ensure that the analysis is correctly determining the total storage
volume. Make sure that the ineffective flow areas are modeled
appropriately.
5.7.0 HYDRAULIC CHANNEL DESIGN CRITERIA
5.7.1 Introduction
Page 34 of 60 Storm Sewer Design Criteria
The hydraulic design of a channel or structure is of primary importance to ensure
that flooding and erosion problems are not aggravated or created. This section
summarizes methodologies, procedures, and criteria which should be used in the
hydraulic analysis of the most common design problems in City of Pearland and
Brazoria County, Texas. In some instances, methodologies and parameters not
discussed in this section may be required. When an approach not presented herein
is required, it should be reviewed early on with the office of the City Engineer.
A. Design Frequencies
All the City of Pearland open channels will be designed to contain the runoff
from the 100 -year frequency storm within the right-of-way, except where
channel improvements are necessary to offset increased flows from a
proposed development. In those cases, the 100 -year flood profile under
existing conditions of development should not be increased.
In areas served by closed systems, storm water runoff should be removed
during the 100 -year frequency storm without flooding of structures. This is
accomplished through the design of the street system, the storm sewer
system, and other drainage/detention systems. .
B. Required Analysis
In designing a facility for flood control purposes, a hydraulic analysis must
be conducted which includes all the factors significantly affecting the water -
surface profile or the hydraulic grade line of the proposed facility. For open
channels, the primary factors are losses due to friction, constrictions,
bridges, culverts, confluences, transitions, and bends. The design of
channels or conduits should generally minimize the energy losses caused by
these factors which impede or disrupt the flow. Factors affecting the
hydraulic grade line in closed conduits are entrance losses, friction losses,
exit losses, and bend losses.
C. Acceptable Methodologies
Several methods exist which can be used to compute water -surface profiles
in open channels. The methodology selected depends on the complexity of
the hydraulic design and the level of accuracy desired. Peak discharges and
discharge hydrographs developed using one of the methodologies described
in Section 5.6.0 must be incorporated into the existing effective HEC -RAS
model in order to determine the impact of any proposed development flood
control facility on the entire channel system.
For the design of proposed channel with flow confined to uniform cross-
sections, either a hand calculated normal depth or direct step computation
is sufficient. Manning's equation should be used for computing normal
Page 35 of 60 Storm Sewer Design Criteria
depth. For designing a non-uniform proposed channel with flow in the
overbanks, the use of HEC -RAS is recommended. Any proposed channel
improvements to an existing collector ditch or creek within the jurisdiction
of the City must be modeled using HEC -RAS and incorporated into the
model used in the Flood Protection Plan.
Bridges, culverts, and expansion and contraction losses are taken into
account in the HEC -RAS computer program. If these losses are significant
and the normal depth or direct step method is employed, the losses must be
included in the backwater calculations. Design criteria for bridges, culverts,
transitions, bends and drop structures are presented in the remainder of this
section.
5.7.2 Open Channel Design
A. Location and Alignment
The first step in designing or improving an open channel drainage system
is to specify its location and alignment. Good engineering judgment must
be incorporated to insure the proposed channel location provides maximum
service to an area while minimizing construction and maintenance costs.
General factors and the City of Pearland criteria which should be taken into
account in locating improved channels are as follows:
a. Follow existing channels, ditches, swales, or other low areas in
undeveloped watersheds. This will minimize the cost of the channel
itself and the underground storm sewer system, and will allow for
overland flow to follow its natural drainage pattern.
b. For safety reasons, channels and roads must not be located adjacent to
one another. Should such a conflict appear unavoidable, the design
must be approved by the office of the City Engineer.
c. The angle at which two channels intersect must be 90 degrees or less
(angle measured between channel centerlines on upstream side on point
of intersection).
d. The minimum radius of curvature for unlined channel bends is three
times the ultimate channel top width and the maximum bend angle for
both lined and unlined sections is 90 degrees. Bend losses and erosion
protection must be included in the hydraulic analysis of severe curves.
B. Existing Cross Sections
For determining existing flood profiles, both the channel section and
overbank areas must be used in the hydraulic calculations. Channel sections
Page 36 of 60 Storm Sewer Design Criteria
must be based on a recent field survey. In some cases, the City of Pearland
may have recent channel improvements information which can be utilized.
Plans of previous channel improvements should only be used for very
preliminary analysis. Overbank areas are best defined by field surveys, but
this is not always practical or economically justified. Elevations in the flood
plain beyond the limits of the channel can be obtained from the best
topographic information available for the study reach.
When designing a channel improvement, the channel sections used should
extend beyond the City of Pearland right-of-way a reasonable distance. The
purpose of including elevations beyond the right-of-way is to avoid a design
which creates ponding adjacent to the right-of-way a reasonable distance
depends on the adjacent terrain, but in no case shall it be less than 20 feet.
C. Typical Design Sections
Typical channel sections have been established which should be used in
designing improved channels. Minimum dimensions are based on
experience of constructing and maintaining channels.
For some applications, other cross section configurations may be necessary.
A proposed cross section different from the typical sections presented
should be reviewed with the office of the City Engineer for approval before
proceeding with design or analysis.
a. Earthen Channels
The following are minimum requirements to be used in the design of all
earthen channels:
1. Maximum earthen side slopes should be 4 (horizontal) to 1
(vertical). Slopes flatter than 4 to 1 may be necessary in some
areas due to local soil conditions. For channels and detention
reservoirs 6 feet deep or greater, side slopes selection shall be
supported by geotechnical investigations and calculations.
2. Minimum bottom width is ten (10) feet unless approved by the
office of the City Engineer or BDD#4.
3. A minimum maintenance berm is required on either side of the
channel of between 10 and 30 feet depending on channel size as
depicted in Table 5.7-1A and 5.7-1B.
These criteria and regulations shall be applicable for all channels that
will be accepted for maintenance by BDD#4 or HCFCD. Small
channels on private property, not draining public water, that do not
Page 37 of 60 Storm Sewer Design Criteria
conform to these criteria shall remain the responsibility of the owner.
These private small channels within the City of Pearland and road -side
ditches along City streets shall be designed in accordance with Section
5.5.0.
TABLE 5.7-1A
KEY TO EASEMENT REQUIREMENTS
CHANNEL
DEPTH 6 8
4 A A
6 A A
8 B B
10 C C
12 C C
14 D D
16 D D
18 D D
CHANNEL BOTTOM WIDTH
10 12 15 20 30 40 1
B B B B C C 1
B B B B C C 1
B C C C C C
C C C C C C
C D D D D D
D D I D D D D
D D I D D D D
D D I D D D D
TABLE 5.7-1B
ULTIMATE MAINTANENCE REQUIREMENTS FOR CHANNELS
KEY TOTAL EACH
VALUE SIDE Side 1
A 30 15 20
B 40 20 25
C 50 25 30
D 60 30 30
UNEVEN
Side 2
10
15
20
30
Larger maintenance berms may be required due to the future needs of
an ultimate channel. Right-of-way requirements for all main outfall
channels are included in the Brazoria Drainage District No 4 Flood
Protection Plan.
1. Backslope drains or interceptor structures are necessary at a
minimum of 1,000 feet intervals to prevent sheet flow over the
ditch slopes.
2. Channel slopes must be re -vegetated immediately after
construction to minimize bank erosion.
3. Flow from roadside ditches must be conveyed to the channel
through a roadside ditch interceptor and pipe.
Page 38 of 60 Storm Sewer Design Criteria
b. Concrete -Lined Trapezoidal Channels
In instances where flow velocities are excessive, channel
confluences create a significant erosion potential, or right-of-way is
limited, fully or partially concrete lined channels may be necessary.
The degree of structural analysis required varies significantly
depending on the intended purpose and the steepness of the slope on
which paving is being placed. Slope paving steeper than 3:1 shall
be designed based on a geotechnical analysis that addresses slope
stability and groundwater pressure behind the paving.
Following are minimum requirements for partially or fully concrete
lined trapezoidal channels:
1. All slope paving should include a minimum 24 toe wall at the
top and sides and a 48 -inch toe wall across or along the channel
bottom for clay soils. In sandy soils, a 36 -inch toe wall is
recommended across the channel bottom.
2. Fully lined cross-sections should have a minimum bottom width
of eight (8) feet.
3. Concrete slope protection placed on 3:1 slopes should have a
minimum thickness of 4 inches and be reinforced with # 3 bars
on 18 -inch centers both ways.
4. Concrete slope protection placed on 2:1 slopes should have a
minimum thickness of 5 inches and be reinforced with # 3 bars
on 15 -inch centers both ways.
5. Concrete slope protection placed on 1.5:1 slopes should have a
minimum thickness of 6 -inches and be reinforced with #4 bars
on 18 -inch centers both ways. Poured in place concrete side
slopes should not be steeper than 1.5:1.
6. In instances where the channel is fully lined, no backslope
drainage structures are required. Partially, lined channels will
require backslope drainage structures.
7. Weep holes may be required to relieve hydrostatic head behind
lined channel sections. Check with the geotechnical
investigation report.
8. Where construction is to take place under conditions of mud
and/or standing water, a seal slab of Class C concrete should be
i
Page 39 of 60 Storm Sewer Design Criteria
placed in channel bottom prior to placement of concrete slope
paving.
9. For bottom widths of twenty (20) feet and greater, transverse
grade beams shall be installed at twenty (20) feet spacing on
center. Grade beams shall be one foot wide, one foot -six inches
deep, and run the width of the channel bottom.
c. Rectangular Concrete Pilot Channels (Low Flow Sections)
In limited right-of-way, it is sometimes necessary to have a vertical
walled rectangular section. Presented below are minimum
requirements for rectangular concrete pilot channels:
1. The structural steel design is based on Grade 60 steel. This
should be confirmed by a design check based on local soil
conditions.
2. Minimum bottom width should be eight (8) feet to allow for
maintenance.
3. For bottom widths twelve (12) feet or greater, a center
depression is required.
4. For bottom widths twenty (20) feet or greater, transverse grade
beams shall be installed at twenty (20) feet spacing on center.
Grade beams shall be one foot wide, one foot -six inches deep,
and run the width of the channel bottom.
5. Minimum height of vertical walls should be four (4) feet.
Heights above this shall be in two (2) foot increments.
Exceptions shall be on a case by case basis.
6. Escape stairways shall be constructed . Escape stairways shall
be located at the upstream side of all street crossings, but not to
exceed 1,400 -foot intervals.
7. For rectangular concrete pilot channels with earthen side
slopes, the top of the vertical wall should be constructed to
allow for future placement of concrete slope paving.
8. Weep holes should be used to relieve hydrostatic pressure.
9. Where construction is to take place under conditions of mud
and/or standing water a seal slab of Class C concrete should be
Page 40 of 60 Storm Sewer Design Criteria
placed in channel bottom prior to placement of concrete slope
paving.
10. Concrete pilot channels may be used in combination with slope
paving or a maintenance shelf. Horizontal paving sections
should be analyzed as one way paving capable of supporting
maintenance equipment.
11. A geotechnical investigation and report shall be performed.
Soil boring shall be obtained at a minimum of every 1,000 feet
to a depth of 1.5 times the proposed channel depth.
D. Water -Surface Profiles
a. General
For steady, gradually varied flow conditions in natural or improved
open channels, the computational procedure known as the standard
step method is recommended for computing water -surface profiles.
The one-dimensional energy equation is solved by using an iterative
procedure to calculate a water -surface elevation at a cross section.
Manning's equation is used to compute energy losses due to friction
(Section 5.7.2.D.b), while losses due to obstructions and transitions
are calculated using the appropriate equations discussed in this
chapter. For cases where the flow is strictly uniform, as determined
by the design engineer, the standard step method can be reduced to
a direct step method or to a uniform flow computation.
The recommended computer program available for computing
water -surface profiles when using the standard step method is HEC -
RAS. As indicated previously the City of Pearland prefers this
program primarily because it is widely accepted and the program
readily facilitates the design of channel improvements.
Good judgment must be exercised when determining cross-section
locations for water -surface profile calculations. Cross sections
should divide the channel into reaches, which approximate uniform
flow conditions. For example, closely spaced cross sections are
required at an abrupt transition such as a bridge, while relatively
uniform channel reaches with no significant changes in conveyance
require fewer cross sections. As a general guideline, the spacing
should not exceed about 1,000 feet.
b. Manning's Equation
Page 41 of 60 Storm Sewer Design Criteria
Manning's equation is an empirical formula used to evaluate the
effects of friction and resistance in open channels. For uniform flow
conditions where the channel bottom and energy line are essentially
parallel, Manning's equation should be used to compute the normal
depth. For gradually varied flow conditions, the slope of the energy
line at a given channel section should be computed using Manning's
equation.
The equation is:
1.49 2 1
Q= x A x R3 x Sz
n
where Q =
n =
A=
R =
S =
total discharge in cubic feet per second.
coefficient of roughness
cross-sectional area of channel in square feet
hydraulic radius of channel in feet
slope of energy line in feet per foot (same as
Channel bottom slope for uniform flow).
Channel and overbank sections may have to be subdivided to
represent differences in roughness across the section. Subdividing
may also be helpful m computing Manning's equation for natural,
compound or non -prismatic sections (References 3.5and 3.9).
c. Manning's "n" Values
Manning's "n" values for design purposes should conform with
Table 5.7-2. An "n" value of 0.04 for unlined channels represents a
moderate vegetal growth. For unlined channels, with a design flow
larger than 10,000 cubic feet per second, "n" value of 0.035 may be
used. For existing, unimproved channels and overbank areas, "n"
values should be determined in accordance with References 3.9,
3.11, and 3.12.
TABLE 5.7-2
MANNING'S "n" VALUES AND ALLOWABLE 25 -YEAR
VELOCITIES FOR CHANNEL DESIGN
Roughness Average Maximum
Coefficient or Velocity Velocity
Manning's (Feet per (Feet per
Channel Description "n" Value Second) Second)
Unmaintained Earthen 0.05 3.0 5.0
Grass Lined:
Predominately Clay I 0.045 3.0 5.0
Page 42 of 60 Storm Sewer Design Criteria
1 Predominately Sand
1 Concrete Lined
1 Articulated Block
Overbanks and Existing
Unimproved Channels
d. Velocities
0.045
0.015
0.045
See References
3.15 and 3.18
2.0 4.0 I
6.0 10.0 i
5.0 8.0
Not Not I
Applicable Applicable
Average and maximum allowable velocities based on 25 -year flows
are given in Table 5.7-2. In the portion of Brazoria County where
sandy soils are known to exist, soils information may be needed to
determine the predominant type of soil and the corresponding
allowable velocities for unlined channels. Maximum velocities also
apply to bridges, culverts, transitions, etc. Where velocities exceed
the maximum allowed, erosion protection must be provided.
e. Flowline Slope
Maximum slopes are generally controlled by the maximum
allowable velocity. Channel slopes shall not be less than 0.05%.
f. Starting Water -Surface Elevations
For design of open channels, starting water -surface elevations at the
channel mouth will generally be based on the normal depth in the
design channel.
In determining actual flood profiles or flood plain delineation, the
water -surface elevation from the outfall channel should be projected
horizontally upstream until it intersects the flood profile on the
design channel. An assumption that the peaks occur at the same
time will generally produce a conservative flood profile.
Otherwise, an analysis of coincident flow may be conducted to
determine the flow in the outfall channel at the time the peak flow
occurs on the design channel.
g. Headlosses
Manning's equation is used to estimate energy or head losses due to
channel friction and resistance. Other sources of losses in open
channels include confluences, transitions, bends, bridges, culverts,
and drop structures. When computing water surface profiles either
by hand or with the help of a computer program, the engineer must
include the significant sources of headloss.
Page 43 of 60 Storm Sewer Design Criteria
E. Confluences
The alignment of confluences is critical with regards to channel erosion and
energy losses caused by turbulence and eddies. The primary variables used
in designing channel junctions are angle of intersection, shape and
dimensions of the channel, flow rates, and flow velocities.
The angle of intersection between the main channel and tributary channels
or storm sewers shall be 30 degrees. Outfalls or junctions perpendicular to
the receiving channel will create severe hydraulic problems, and therefore,
will not be allowed without approval by the office of the City Engineer.
Any protective lining must extend far enough upstream and downstream on
both channels to prevent serious erosion. The slope protection must be
carried up to at least the 10 -year flood level in both channels. A good grass
cover must also be established from the edge of the protection to the top of
bank.
If the main channel flowline is lower than the side channel flowline, an
erosion control structure must be used in the side channel.
F. Transitions
a. Design
Transitions in channels should be designed to create a minimum of
flow disturbance and thus minimal energy loss. Transitions
generally occur at bridges or culverts, and where cross-sections
change due to hydraulic reasons or right-of-way restrictions. The
transition can consist of either a change in cross-section size or
geometry.
All angles of transition should be less than 12 degrees (20 feet in
100 feet). When connecting trapezoidal and rectangular channels,
the warped or wedge type transition is recommended. If super-
critical flow conditions are encountered, standing waves,
superelevation, and hydraulic jumps must be considered.
b. Analysis
Expansion and contraction losses must be accounted for in
backwater computations. Transition losses are usually computed
using the energy equation and are expressed in terms of the change
in velocity head from downstream to upstream of the transition. The
head loss between cross sections is expressed by:
Page 44 of 60 Storm Sewer Design Criteria
V2 V2
h� = C ---
2g 2g
where: hi_ = head loss (feet,
c = expansion or contraction coefficient
V2 = average channel velocity of
downstream section (feet per second),
V1 = average channel velocity of upstream
section (feet per second), and
g = acceleration of gravity (32.2 ft/sec2).
Typical transition loss coefficients to be used in HEC -RAS are given
below:
Coefficient
Transition Type Contraction Expansion
Gradual or Warped 0.10 0.30
Bridge Sections, Wedge, or 0.30 0.50
Straight Lined
Abrupt or Squared End 0.60 0.80
When computing the backwater profile through a transition,
engineering judgment must be used in selecting the reach lengths.
Smooth transitions require fewer computation steps than the abrupt
transitions.
G. Bends
a. Design
Channel bends or curves should be as gradual as possible to reduce
erosion and deposition tendencies. For channel bends with a radius
of curvature measured from the channel centerline of less than three
times the top width of the ultimate channel, slope protection is
required. For both lined and unlined channels, a 90 degree bend is
the maximum curve allowed. Erosion protection on bends must
extend at least along and 20 feet downstream of the curved section
on the outside bank. Additional protection may be required on the
channel bottom and inside bank, or further downstream than 20 feet
if the channel geometry and velocities indicates a potential erosion
problem.
Page 45 of 60 Storm Sewer Design Criteria
b. Analysis
Head losses should be incorporated into the backwater computations
for bends with a radius of curvature less than three times the channel
top width. Energy loss due to curve resistance can be expressed as:
hL = cfV2/2g
where hL = head loss (feet),
cf = coefficient of resistance,
V = average channel velocity (feet per second), and
g = coefficient of gravity (32.3 feet/second).
Guidelines for selecting cf can be found in Reference 3.15.
HEC -RAS has the ability to incorporate a bend loss computation in
terms of a minor loss coefficient ranging from 0.0 to 1.0. If HEC -
RAS is used and bend losses are significant, the loss must be added
at the appropriate point in the minor loss table. Bends with a radius
of curvature greater than three times the top width of the channel
generally have insignificant losses and no computation is required.
5.8.0 DETENTION SYSTEM DESIGN
5.8.1 Introduction
In situations where on-site storage of stormwater runoff is the most effective way
to allow development of properties without increasing the flood potential
downstream, detention systems will be permitted. This section of the Manual
presents background information on stormwater storage techniques and detailed
guidelines and criteria for the design of stormwater storage facilities.
A. Types of Storage Facilities
The physical features of a particular site, as well as the type of development
proposed, will dictate, in many cases, the type of detention storage facility
that may be utilized. Since detention facilities are more often than not
designed to remain dry, they can provide dual purpose functions such as
parking lots and recreational areas. In limited instances, on-site detention
facilities have been designed to be buried underground and thus are
completely out of sight.
All of these types of facilities are considered acceptable methods of
stormwater detention and can be designed hydraulically to accomplish the
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intended purpose. All stormwater detention facilities are subject to periodic
inspection by the City Engineer to insure proper construction and
maintenance.
Dual use of stormwater detention facilities is encouraged. However, when
a dual use is proposed, such as recreation, a joint use agreement is required
between the owner and the entity sponsoring the secondary use. This
agreement must outline the maintenance responsibilities of the entity and of
the owner and must be submitted to the City of Pearland for approval. For
privately maintained or dual use systems, each stormwater detention facility
will be reviewed and approved by the City only if the following assurances
can be provided:
a. Adequate storage is available to provide necessary peak flow reduction;
b. The facility will perform as designed over the expected life of the
project;
c. Provisions for maintenance, including long-term funding for
maintenance, are adequate to insure the facility does not detract from
the value of adjacent properties; and,
d. The facility will be maintained to operate long term and continue to
function as designed.
Detention ponds may be either on-site or off-site facilities. An off-site
detention basin is defined as one that is located on a City of Pearland,
BDD#4, or HCFCD ditch and is receiving runoff from areas significantly
larger than the development project under design. An on-site basin
generally receives runoff from a small drainage area consisting primarily of
one development project. In the discussions that follow, the design methods
presented are generally oriented to on-site detention facilities. Specific
reference will be made to methods for off-site facilities.
Projects located in the uppermost reach of a drainage basin may use the
volume of stormwater stored in pipes, ditches, or streets as credit for the
part of the detention requirement. Storage will be credited for street volume
up to the maximum allowable ponding depth per these criteria. Sheet flow
analysis must be performed to insure that for extreme events, the ponding
level in the streets will not exceed the maximum ponding level.
B. Geotechnical Design
Before initiating final design of detention ponds over 6 feet deep and 2 acres
in size, a detailed soils investigation by a geotechnical engineer shall be
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undertaken. Geotechnical investigation, at a minimum, the study should
address:
a. The ground water conditions at the proposed site;
b. The type of material to be excavated from the pond site and its suitability
for fill material;
c. If an embankment is to be constructed, adequate investigation of
potential seepage problems through the embankment and attendant
control requirements, the availability of suitable embankment material
and the stability requirements for the embankment itself.
d. Potential for structural movement on areas adjacent to the pond due to
the induced loads from existing or proposed structures and methods of
control that may be required.
e. Stability of the pond side slopes.
5.8.2 Hydrologic Design
Detention basin design shall conform to City of Pearland criteria, BDD#4 rules, or
HCFCD criteria on a case-by-case basis as approved by the office of City
Engineer. The hydrologic methods for detention design should be in accordance
with Section 5.6.0 of this Manual. The City of Pearland criteria for design of
stormwater mitigation detention is categorized as Small Project (Projects 2 acres
or smaller), Medium Project (Projects larger than 2 acres, but less than 30 acres),
or Large Project (Projects larger than 30 acres).
5.8.3 On -Site Facilities
A. Small Projects (Projects 2 Acres or Smaller)
Small Projects are defined as those projects that are 2 acres or smaller. If a
project causes change in runoff coefficient (existing vs. developed) times
the area of the development equal to or less than 0.7, the project may be
eligible for purchasing regional detention. Mitigation of such facilities will
be incorporated within the City of Pearland regional detention facilities,
provided capacity is available and the development is within the detention
facility service area. If regional capacity is not possible, on-site detention
will be required based 0.65 ac -ft. per acre and the outlet will be sized based
on the procedure presented in Section 5.8.3.B (below). In this case the
volume that is calculated using 0.65 ac -ft. per acre will be considered to be
the 100 -year volume. The 10 -year and 3 -year volumes will be considered
to be 57% and 39% of the 100 -year volume, respectively. The generation
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of runoff hydrographs and the routing of flood flows are not required for
Small Projects.
B. Medium Projects (Projects Larger Than 2 Acres, But Less Than 30 Acres)
Medium Projects in the City of Pearland method will have their mitigation
detention volumes calculated using the methodology presented in Appendix
A. All calculations shall be presented to the office of the City Engineer,
including maps of suitable scale showing the flow paths used to calculate
the existing and developed time of concentration. See the example at the
end of Appendix A in this manual. Hydrograph routing through the
detention basin is not required. The outflow structures (low level pipe(s) or
opening(s) and high level weir) will be sized as follows:
a. Determine the 100 -year storage elevation in the basin.
b. Determine the minimum flow line elevation for the outflow
structure.
c. Use the orifice equation to compute the opening size(s) as follows:
Q = CA.j2gH ,
Where:
Q = Basin Outflow (cfs),
C = Pipe Coefficient,
A = Restrictor cross-sectional area,
g = Acceleration due to gravity (32.2 ft/s2), and
H = The elevation difference between the
detention basin water surface
elevation for the design storm and the
top of the restrictor pipe (feet).
Round up to the next half -foot diameter for restrictor pipes above 18 -inch
diameter. Some additional blockage of the pipe may be necessary to obtain
the correct restrictor area (A). No restrictor pipes shall be less than 6 inches
in diameter.
For ponds discharging into creeks or ditches, the outfall structure shall be
designed for the 3, 10 and 100 -year storm frequencies. Determine the 3, 10
and 100 -year detention volumes and compute the water surface elevations
to determine restrictor size to detain to undeveloped flow rates. Use a
vertical structure or multiple pipes separated vertically with the top of the
structure or flowline of the second pipe set at the 3 -year or 10 -year water
surface so as to be over topped in greater storms. A weir set below the 100 -
year developed water surface elevation shall be used to discharge during the
100 -year design condition. This weir should be sized so that the peak
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discharge does not exceed the 100 -year pre -developed discharge with the
basin full and the tailwater elevation at or below the top of the discharge
pipe.
Storm events in excess of the 100 -year event must be considered in the
design of detention facilities from the standpoint of overtopping. For a
detention facility that is an excavated pond and has no dam associated with
it, the outflow structure must be designed with an overflow structure or
swale. This will allow the passage of extreme events with no adverse
impacts to adjacent structures. For detention facilities with a dam, the
possibility of dam failure must be considered as part of the design. Specific
dam criteria for storm events in excess of the 100 -year design storm shall
be established by the office of the City Engineer on a case-by-case basis.
C. Large Projects (Projects larger than 30 acres)
Large projects may under certain conditions have on-site detention
facilities. Unless FEMA submittals are required, or a downstream impact
analysis is required, large on-site projects will be analyzed using the
Malcolm Method, as discussed in Section 5.6.0 of this Manual.
The design of a detention basin basically consists of the following major
phases:
a. Determination of a 3 -year, 10 -year and 100 -year 24-hour design storm
inflow hydrograph to the proposed detention basin.
b. Determination of the maximum 3 -year, 10 -year and 100 -year 24-hour
design storm allowable outflow rate from the detention basin. Outflow
rates shall be equal to or less than historical rates or rates for pre -project
conditions.
c. Design tailwater elevation will be assumed to be equal to the top of the
outflow pipe, unless special tailwater conditions prevail .
d. Preliminary sizing of basin storage capacity and the outflow structure.
e. Routing of design inflow hydrograph through the basin, and adjustment
of storage and outflow structure, if required, to ensure that the maximum
allowable outflow rate is not exceeded. This routing should be
performed in an appropriate computer program such as ICPR (or others
as approved by the City Engineer) or a spreadsheet with proper
documentation. The outflow structure shall include a pipe or pipes sized
to restrict discharge to both the allowable 3 -year and 10 -year outflow
rate and the allowable 100 -year design flow.
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f. Analysis of the hydraulic gradients for storm sewers and inflow
channels entering the basin to insure that these systems will operate
properly under design water surface conditions in the basin.
g.
Analysis of rainfall events in excess of the design frequency for
structural and flood considerations, including provisions for a high level
overflow structure. This design shall consider the possibility that should
the normal outlet structure from the basin fail, the storm water can pass
through, over or around the detention basin without damaging adjacent
structures.
h. Investigation of potential geotechnical and structural problems.
5.8.4 Off -Site Facilities
Off-site detention facilities will generally be regional in nature. The facility may
be sized for one development, but will be designed to serve the entire watershed by
reducing the flood potential of a stream. Most of these facilities are envisioned to
be adjacent to a channel to receive flood water from the main drainage artery
through a system of multistage inlet pipes and high level weirs.
For the design of an off-site detention basin, the hydraulics of the stream and flood
damage relationship of the watershed must be evaluated. This will be performed
under the direction and advice of the office of the City Engineer. This evaluation
will result in flood frequency/stage-damage estimates of the stream.
Upstream discharge of unmitigated runoff into a stream, on which capacity is
reserved in a regional detention basin, may be allowed if analysis of stormwater
flow demonstrates that flood water surface elevations will not cause flooding
between release point and the detention reservoir.
Sizing of the multistage inlets will be based on a plan that will be most beneficial
to the downstream community. Side flow diversions will also be developed and
evaluated by iterations to evaluate the impact of the diversion on the downstream
hydrographs. The arrangement of pipes/weirs shall be designed to minimize
property damages due to different storms within the entire area served by detention.
The office of City Engineer will advise the design engineer in regards to specific
design configurations.
Off-site facilities will be analyzed using HEC -HMS modeling techniques as
discussed in Section 5.6.0. The 3 -year, 10 -year and 100 -year will be performed.
Input from the office of City Engineer is recommended to determine the most
appropriate level to set diversion structures for watershed -wide flood damage
mitigation. These facilities will generally be located along a FEMA studied stream
with adequate models available for the analysis. Routing of the inflow 3 -year, 10 -
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year and 100 -year hydrographs through the detention basin may also be performed
using a computer model such as ICPR or other detention reservoir models approved
by the office of City Engineer. Set the tailwater level in the receiving stream equal
to the top of the outfall pipe, unless special tailwater conditions prevail.
For off-site facilities, the existing models will be used to develop a proposed (post
project) condition model(s). For such analysis, the proposed development will not
be isolated as a separate subarea. The existing hydrograph parameters (Tc+R) will
be modified or revised to reflect changes in percent land urbanization (DLU),
percent channel improvement (DCI). Percent channel conveyance (DCC), and
percent impervious cover. Watersheds being developed may lose some or most of
the percent ponding (DPP) that may exist in the rural portion of certain watersheds.
Because the project area will not be modeled as a separate subarea, the high inflow
to the main drainage artery will not be evident in the model. Rather, because the
subarea parameters will be revised to reflect the impact of the project, the total
hydrograph along the main artery will increase without detention mitigation. The
diversion of the flood waters near the peak of the hydrograph will be effected
through the use of multilevel pipes and a weir to mitigate the increase flow to
downstream reaches.
5.8.5 Pump Detention System
All storm water detention facilities requiring mechanical pumping systems are
generally prohibited, with the exception of pumping of dead storage (maintenance
or amenity water stored at or below the discharge pipe control level). However,
pumped detention shall be allowed under the following conditions:
a. The discharge delivery system shall not have peak discharge and/or peak stages
that exceed the pre -developed peak values at any point in time for the 3 -year,
10 -year and 100 -year design storm events.
b. Two pumps minimum shall be required, each capable of providing the design
discharge rate. If three pumps are used, any two pumps must be capable of
handling the design discharge rate. The total discharge pumping rate shall not
exceed the design discharge rate.
c. A gravity overflow route and outfall must be submitted to the office of City
Engineer for approval. Pumping from detention into an existing storm sewer is
prohibited unless the pre -developed land already drains into an inlet and storm
sewer system.
d. Pumped detention shall not be allowed for detention basins that collect public
water runoff, except for detention basins owned, operated and maintained by
the City or Brazoria Drainage District #4. Public water runoff shall be defined
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as runoff water that originates from the property of more than one property
owner.
e. For detention basins collecting non-public (originates from a single property
owner) runoff water that utilize mechanical pumping systems, a cash amount
equal to the fair market value cost of the pumps and their installation shall be
deposited with the City and placed into escrow prior to approval of the final
plat, or prior to the issuance of a building permit if platting is not required. This
deposit shall be placed into a permanent interest bearing account for the use of
the City to maintain the pump system in the event the owner fails to maintain
the pump system in accordance with the requirements of the City.
f. Fencing of the control panel is provided to prevent unauthorized operation and
vandalism.
g. Adequate assurance is provided that the system will be operated and maintained
on a continuous basis.
h. Emergency source of power is provided for those cases that loss of power
during a 100 -year flood event would cause property damage.
i. Sensors must be placed so that pumps would remain off during a rain event.
Additionally, sensors must be placed so that pumping will not occur when the
level of water in the receiving system is at or above 1/4 of its full depth.
J•
The minimum detention rate shall be 0.70 ac-ft/ac.
k. No more than 75% of the total pond capacity shall be pumped.
1. Pumping from detention ponds into an existing storm sewer is prohibited unless
the pre -developed land already drains into that system and that system has
capacity for those undeveloped flows.
m. The Operator shall provide the office of City Engineer with a quarterly
operational report that shall indicate the operational times, total hours of
operation, and the amount pumped. This report shall be delivered to the office
of City Engineer at end of each quarter, no later than 15th of the month.
n. The City shall have the right to enter the property and inspect the operation of
the system at any time for any reason.
o. Failure to maintain the pump station in working order is a violation of these
requirements.
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It is recommended that if a pump system is desired, approval by the City of Pearland
of the preliminary conceptual design be obtained before any detailed engineering
is performed.
5.8.6 Structural and Geometric Parameters
A. General
The structural design of detention basins is very similar in many ways to
wide bottom channels. Therefore, the design requirements concerning side
slopes and berms are as outlined in Section 5.7.2 for channels. Design
considerations addressed specifically in this section deal with the basin
bottom and outfall structure.
Two types of detention facilities are acceptable in the City of Pearland. The
first is a naturalized basin in which standing shallow pools of water and
muddy areas are allowed to exist along the bottom of the basin and support
natural or wetlands vegetation. This type of basin is only maintained around
the sides and perimeter and involves special design considerations at the
outfall structure. Designing this type of facility must be approved by the
City and must consider the aesthetics of the surrounding area. The second
type of detention facility is a manicured or well-maintained basin, which is
mowed regularly and is designed to stay dry between rainfall events. This
type of facility may be more aesthetically pleasing in heavily populated
areas and is more amenable to multiple uses such as parks or ball fields.
The design considerations for each facility are outlined below.
B. Bottom Design for Natural and Permanent Pool Basins
The bottom of a detention basin, which is intentionally meant to support
natural vegetation, should be designed as flat as practical to still maintain
positive drainage to the outfall structure. Side -slopes should be designed to
allow for regular maintenance and be grass -lined with a preferred 6 to 1 side
slope but no steeper than 4 to 1 maximum. The bottom should be graded
toward the outfall structure at a minimum transverse slope of 0.001 feet per
foot. Selected vegetation may be introduced to the bottom of the basin to
encourage a particular habitat. Other design requirements for channels
should be followed, including maintenance berms, backslope drains and
erosion protection measures. A maintenance plan to remove trash debris
and excessive siltation must be provided to and approved by the City. The
depth of permanent pool shall not be less than 4 feet. Additional storage
volume may be required by the City to offset predicted siltation based on
experiences with nearby storage facilities.
C. Bottom Design for Manicured Basins
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The design of the detention basin bottom to remain dry and aesthetically
manicured is very important from the standpoint of long term maintenance.
A pilot channel is required to facilitate complete drainage of the basin
following a runoff event. A lined concrete channel should have a minimum
depth of 6 inches and a minimum flowline slope of .002 feet per foot. An
unlined pilot channel should have a minimum depth of two feet, a minimum
flowline slope of .005 feet per foot, and maximum side slopes of 4:1.
Bottom slopes of the detention basins should be graded towards the low -
flow pilot channel or outfall. The transverse slope of the bottom should be
a minimum slope of 1 %, with 2% preferred.
Detention basins which make use of a channel section for detention storage
may not be required to have pilot channels, but should be built in accordance
with the requirements for channels, including side slopes, maintenance
berms, back slope drains and erosion protection measures previously
discussed.
D. Outlet Structure
For low tail water conditions, the outlet structure for a detention basin is
subject to higher than normal headwater conditions and possibly erosive
velocities for prolonged periods of time. For this reason the erosion
protective measures are very important.
Reinforced concrete pipe used in the outlet structure should conform to
ASTM C-76 Class III with compression type rubber gasket joints
conforming to ASTM C- 443. HDPE or aluminized steel pipes may also be
used. Pipes, culverts and conduits used in the outlet structures should be
carefully constructed with sufficient compaction of the backfill material
around the pipe structure as recommended in the geotechnical analysis.
Generally, compaction density should be the same as the rest of the
structure. The use of pressure grouting around the outlet conduit should be
considered where soil types or conditions may prevent satisfactory backfill
compaction. Pressure grouting should also be used where headwater depths
could cause backfill to wash out around the pipe. The use of seepage cutoff
collars is not recommended since such collars are often inadequately
installed and prevent satisfactory backfill compaction. A concrete control
structure with a grate area equal to ten (10) times the outfall pipe area shall
be constructed. Concrete paving extending from the outfall area into the
basin a distance of 10 feet shall be placed on the bottom of the basin for
maintenance of the structure. Adequate steel grating around the outfall pipe
intake must be designed to prevent clogging of the pipe from dead or
displaced vegetation.
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The concrete or articulated block on filter fabric spillway for the 100 -year
discharge or greater flows shall extend down the bank to the bottom of the
channel and up the far side.
E. Additional Design Considerations
The following items describe additional design criteria associated with
detention basins.
a. Erosion Control
Adequate erosion control and re -vegetation shall be accomplished
during and following construction of the basin. The City of Pearland
will allow articulated block on filter fabric as an acceptable means of
slope protection.
b. Safety, Aesthetic Consideration and Multi -Purpose Use
The use of a detention basin facility generally requires the commitment
of a substantial land area for the basin. The City of Pearland recognizes
that such a facility may be used for other purposes which are compatible
with the primary intended purpose of providing flood control. Basins
may be utilized as parks and recreational facilities on a case-by-case
basis. Also, a parking area may be used for a portion of the storage as
long as the 100 -year water depth is no greater than 9 inches where cars
are parked. The proposed use and the facilities to be constructed within
the basin area must be specifically approved by the City of Pearland.
The City of Pearland will not assume any maintenance responsibility on
or within private detention facilities.
5.9.0 MISCELLANEOUS DESIGN CONSIDERATIONS
5.9.1 Storm Sewer Outfalls
All storm sewer outfall structures should be constructed in accordance with
standard details and Brazoria Drainage District 4 details . Design criteria for outfall
structures is as follows:
a. All storm sewer outfall pipes within the City of Pearland right-of-way must be
reinforced concrete pipe with rubber gasket joints, aluminized steel pipe, or
HDPE with a minimum diameter of 18 inches.
b. All backslope drains shall be 24 -inch reinforced concrete pipe, aluminized steel
or HDPE.
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c. A standard City of Pearland manhole or junction box must be outside of the
City of Pearland ultimate right-of-way. Where a road or railroad right-of-way
is located adjacent to the channel, the manhole may be placed within the City
of Pearland right-of-way.
d. The grade of the pipe should be that required to produce a three feet per second
velocity when flowing full.
e. Erosion protection is required for all outfall pipes.
f. Effluent outfalls from treatment plants shall have a paved invert, and riprap.
5.9.2 General Control Structures
Special erosion and velocity control structures will generally include stilling basins,
baffled aprons, straight drop spillways, sloped drops, and impact basins. Due to
the hydraulic and earth loads encountered through these structures, the structural as
well as the hydraulic design is very critical.
A geotechnical engineering investigation to determine the characteristics of the
supporting soil is required for major hydraulic structures. For example, a 2 -foot
sloped drop would not require a soils investigation, whereas a 5 -foot straight drop
structure would.
5.9.3 Straight Drop Spillway
Straight drop spillways are usually constructed of steel sheet piling with concrete
aprons. Steel sheet pile drop structures can sometimes be considered a temporary
structure.
The distance erosion protection aprons extend upstream and downstream of the
drop is determined using hydraulic analysis. The City of Pearland recommends
using concrete paving upstream and immediately downstream of the drop. Because
of the additional impact load on the downstream slope paving, a 6 -inch thick pad is
recommended. Articulated blocks placed on geotextile fabric should be used at the
ends of the concrete paving to decrease flow velocities and protect the concrete toe.
The drop structure should be designed for active and passive soil forces. Design
calculations are required for each drop structure along with a copy of a geotechnical
report defming soil characteristics of the site.
5.9.4 Baffle Chutes
See Reference 3.23 for hydraulic and structural criteria regarding baffle block
chutes.
Page 57 of 60 Storm Sewer Design Criteria
5.9.5 Sloped Drop Structures
Sloped drop structures can be made of either monolithic poured -in-place reinforced
concrete or articulated cellular concrete block mats. The same design principles
hold true for sloped drop structures as do for straight drop structures; i.e., the draw
down curve and hydraulic jump must be contained within the structures or stilling
basin.
The sloped drop structure should have 24 -inch toe walls on the upstream and
downstream ends. The sides of the structure should have 18 -inch toe walls.
If an articulated cellular concrete block drop structure is used, the blocks should be
bedded on a filter fabric. The fabric should be heavy duty and designed for the
specific soil condition. The size and weight of the blocks should be designed for
shear forces.
5.9.6 Utility Crossings
Approval must be obtained from the office of the City Engineer for all utility lines
which cross a flood control facility. The utility crossing should be designed to
minimize obstruction of the channel flow and conform with the ultimate channel
cross-section. Contact the office of City Engineer for information regarding the
ultimate channel section and ultimate channel right-of-way at a proposed crossing
prior to design.
All utility lines under channels should be constructed with the top portion of the
conduit a minimum of five (5) feet below the projected flow line of the ultimate
channel as shown in Exhibit 9-4. When appropriate, facilities may be constructed
on special utility bridges or trestles in accordance with standard bridge design
criteria. Pipes or conduits spanning the channel should be located above the top of
banks for hydraulic and maintenance reasons. For utility crossings on street
bridges, contact the appropriate government body for approval.
All manholes required for the utility conduit shall be located outside the City of
Pearland ultimate right-of-way. Backfill within the City of Pearland right-of-way
shall be in accordance with the backfill requirements specified by the respective
city, county, or utility company.
5.10 EASEMENT AND RIGHTS-OF-WAY
To the extent practical, storm sewers shall be placed in reserves, public road rights-of-way
or permanent access strips with drainage easements.
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Storm sewers shall have a minimum 20 -foot easement. In the event of extreme depth (over
10 feet) the width shall be the diameter or width of the sewer plus twice depth to the center
of the sewer.
Pipes shall be centered within the limits of the reserve and easement.
5.11 SUBMITTAL
5.11.1 Preliminary Submittal
Submit for Review and Comment:
One line drawings are recommended and are required as part of the platting
process. One line drawings should include:
a. Approximate definition of lots and street patterns.
b. The approximate drainage areas and design flows for each system.
c. A definition of the proposed drainage system and stormwater mitigation
by single line.
d. The proposed pipe diameters.
e. Any proposed drainage easements.
f. Floodplain boundary, if any.
g. Proposed management of perimeter drainage.
5.1 1.2 Final Design
Submit the Following for Approval:
a. Preliminary mark-ups and copies of any documents which show approval of
exceptions to these design requirements.
b. Design calculations for storm line sizes and grades, and for detention
facilities, if any.
c. Design calculations for the hydraulic grade line of each storm sewer line or
ditch, and for detention facilities, if any.
d. Contour map and drainage area map of the project.
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e. Plan and profile sheets showing storm water design (public facilities only).
f. Projects located within a floodplain boundary shall:
1. Show the floodplain boundary or floodplain area, as appropriate, on the
one -line drawing or drainage area map.
2. Comply with all applicable floodplain development ordinances of the
City of Pearland.
g. Soil boring logs with construction drawings.
5.12 QUALITY ASSURANCE
Prepare calculations and construction drawings under the supervision of a Professional
Engineer licensed in the State of Texas. The final construction drawings and all design
calculations must be sealed, signed, and dated by the Professional Engineer responsible
for the development of the drawings.
5.13 DESIGN ANALYSIS
All projects shall be tied to North American Vertical Datum (NAVD), 1988, 2001
adjustment. The City of Pearland vertical control (benchmarks) used to prepare the 2 -foot
City of Pearland topographic maps shall be used where available. For areas in or adjacent
to flood plains, equations shall be used to calculate the base flood elevation (from Flood
insurance Rate Maps or subsequent locally adopted flood elevation) to the 1973, or 1978
adjustment. In the event GPS surveying is used to establish benchmarks, at least two
references to benchmarks must be identified.
Plan sets will include a drainage area map, which will contain calculations of runoff flow
rates.
All drainage systems for curb and gutter pavements shall be underground closed conduits;
individual residential lot drainage is exempt. Drainage systems for pavements without curb
and gutter shall be roadside open -ditch sections.
Soil boring with logs shall be made along the alignment of all storm sewers having a cross
section equal to or greater than 42 inches in diameter or equivalent cross section area.
Boring should be taken at intervals not to exceed 500 linear feet and to a depth not less
than5 feet below the flow line of the sewer. The required bedding will be determined from
the soil boring and shall be shown in the profile of each respective storm sewer.
Page 60 of 60 Storm Sewer Design Criteria
APPENDIX A
DETENTION STORAGE VOLUME CALCULATIONS
FOR
SMALL AND MEDIUM PROJECTS
The small and medium size projects are most sensitive for short duration, high intensity storms.
Medium projects (between 2 and 30 acres) will be based on SCS concepts using triangle
hydrograph approximations. The runoff volumes are based on a triangle hydrograph with a runoff
duration equal to twice the time of concentration (Tc) of the existing, pre -project condition. This
concept is illustrated in Figure A-1.
Figure A-1.
Time
The variables in Figure A-1 are defined as follows and should be in consistent units when making
calculations:
Tc,
Ted
Qe
• Time of concentration for the existing (predeveloped) watershed
or subarea
• Time of concentration for the proposed or developed watershed
or subarea
• Existing condition peak discharge (calculated using the rational
method)
A-1 Storm Sewer Design Criteria
Qd
Q.
= Developed condition peak discharge (calculated using the rational
method)
= Flow corresponding to the point in time where the flows of the
developed and existing conditions hydrographs are equal
In order to determine the required storage volume VS for onsite detention, it is necessary to
determine the incremental volume V, of runoff due to development. In Figure A-1 V; is the
difference between the areas of the developed runoff hydrograph and the existing runoff
hydrograph up to the time period equal to twice the developed time of concentration (Tcd). This
is expressed mathematically as:
V,. =V d
— VQ
Where Vd and Ve are the developed and existing conditions runoff volumes up to the time period
equal to two times Tcd, respectively.
Determining Vd is simple and can be calculated by multiplying the developed peak discharge by
the developed time of concentration. Determining Ve is slightly more tedious and requires first
determining the point Q, shown in Figure A-1. It can be shown that doing so will result in the
equations given below, which should be used for design purposes.
The design engineer must first determine whether the point representing the existing conditions
peak discharge Qe lies inside or outside the region bounded by the developed runoff hydrograph.
To do this, first calculate the following ratios:
Y=
Cd
and
TCe
a=Qe
Qd
If a >— 2-y, Qe lies outside the region bounded by the developed runoff hydrograph Otherwise, Qe
lies inside this region. Next, the incremental increase in runoff V, is calculated using one of the
equations below:
= Qd Tcd
Or
fora >_ 2-y (1)
y+a+crAy+a-4)
V = Q(, Tc(, fora < 2-y (2)
y—a
A-2 Storm Sewer Design Criteria
After determining V,, the required volume of storage VS should be calculated using the equation
below:
V _ 13.5V. (3)
D @ 2Tcd
Where
D@2Tcd = Depth at time equal to 2 Ted, or the maximum rainfall depth (in), from
depth -duration -frequency curves at the time equal to twice the developed
conditions time of concentration (min).
A-3 Storm Sewer Design Criteria
CITY OF PEARLAND
CHAPTER 6
ROADWAY DESIGN CRITERIA
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 15 Roadway Design Criteria
CHAPTER 6
ROADWAY DESIGN CRITERIA
6.1 GENERAL
6.1.1 All construction plans containing proposed roadways, sidewalks, and
driveways in a public right-of-way shall be reviewed by the office of the
City Engineer for all improvements within the city limits.
6.1.2 All new streets installed within the city limits shall be concrete curb and
gutter. New street construction that utilizes roadside ditches for storm
water drainage is discouraged and must receive specific approval of the
City.
6.1.3 Street design shall conform to all applicable planning tools such as the City
of Pearland Unified Development Code requirements, latest edition of the
Texas Manual on Uniform Traffic Control Devices, Pearland
Comprehensive Plan, Pearland Major Thoroughfare Plan, and Master
Parks Plan and Master Trails Plan. Other consideration for design shall
include roadway function, capacity, levels of service, traffic safety, the
AASHTO Policy on Geometric Design of Highways and Streets,
Americans with Disabilities Act (ADA) regulations on accessibility
design, pedestrian safety, and all utility locations including gas, cable and
power lines. Any deviation using other materials or other design criteria
requires prior approval by the City.
6.1.4 Design shall conform to the City of Pearland construction details where
applicable. These criteria shall not apply to proposed streets projects
located in Texas Department of Transportation (TxDOT) or Harris County
owned and/or maintained right-of-way.
6.1.5 On a case-by-case basis the City of Pearland reserves the right to allow
deviations from these design criteria. These design criteria are not
intended to cover repairs to -existing streets or street extensions when such
repair work or extensions are performed by City of Pearland in whole or in
part. These criteria are not intended to cover existing streets within the
City of Pearland that do not already conform to these criteria
6.1.6 These are to be considered minimum guidelines but the City of Pearland
may require a Traffic Impact Analysis at no cost to the City where the City
of Pearland deems it is warranted.
6.2 ROADWAY CLASSIFICATIONS
6.2.1 Major Thoroughfare, 4 or 6 lanes, divided roadway: Shall provide a high
degree of mobility, serve relatively high traffic volumes, have limited
access, have high operational speeds and serve a significant portion of
through travel and traffic movement by serving as the major traffic
Page 2 of 15 Roadway Design ('ritena
corridors. Usually constructed within a minimum 120 ft. wide right-of-
way.
6.2.2 Secondary Thoroughfare, 4 lanes, divided or undivided roadway: Serve
same function as principal arterials but typically have a lower traffic
volume. Usually constructed within a minimum 100 ft. wide right-of-way.
6.2.3 Major Collector, 4 lanes, undivided roadway: Shall be used in multi-
family, commercial or industrial areas as well as secondary streets.
Usually constructed within a minimum 80 ft. wide right-of-way
6.2.4 Minor Collector, 2 or 3 lanes, undivided roadway: Shall be used for minor
collector streets in single family residential areas or local multi -family
residential, commercial, or industrial areas as well as secondary streets
where defined. May have two travel lanes and a center continuous left -
turn lane, or 2 lanes with on -street parking. Usually constructed within a
minimum 60 ft. wide right-of-way.
6.2.5 Local, residential, 2 lane, undivided roadway: Include internal and access
streets that allow direct access to residential properties and similar traffic
destinations and typically have low design speeds and low traffic volumes.
Usually constructed within a minimum 50 ft. wide right-of-way.
6.3 GEOMETRIC STREET DESIGN STANDARDS
6.3.1 Minimum geometric street design standards for number of lanes, lane
widths, right-of-way widths, and median widths shall be as follows:
Right -of -Way Width
Curb Back to Curb Back Distance
Median Width(bc-bc)0
Distance from Curb Back to ROW line
Distance from ROW Line to Sidewalk
Max. Number of Lanes (one direction)
(1)
Major
Thoroughfare
120 feet
N/A
18 feet
14 feet
Varies
3
With on -street parallel parking.
Table 6.1
Major
Thoroughfare
120 feet
N/A
42 feet
14 feet
Varies
2
(2) Median turning lanes are included in median widths.
Secondary Major Minor Local
Thoroughfare Collector Collector Street
100 feet 80 feet 60 feet 50 feet
N/A 45 feet 37 feet 28 feet
18 feet N/A N/A N/A
16 feet 17.5 feet 11.5 feet 16 feet
Varies Varies Varies Varies
2 2 1 1
6.3.2 The design speeds shall conform to the following design standards. The
posted speed limit shall never exceed the design speed. The design speed
should be a minimum of 5 mph greater than the posted speed limit.
Table 6.2
Urban
Thoroughfares
Collectors
Local
40-60 Nil
30-50 rrlpi
30 mph
Page 3 of 15 Roadway Design C'nteria
6.3.3 The maximum grade allowed refers to the uphill or downhill slope of the
street and shall conform to the following design standards:
Table 6.3
Table 6.4
Collectors
Type of Terrain
Level
Design Speeds (mph)
20 1 25 1 30 1 35 1 40 1 _45 )50 1 55 1 60
Maximum Grades (%)(I)
9 1 9 1 9 1 9 )9 1 8 I 7 ) 7 I 6
(1) Short lengths of grade in urban areas, such as grades less than 500 ft in length, one-
way downgrades, and grades on low-volume urban collectors may be up to 2% steeper
than the grades shown above. Note: Sidewalks along these roadways shall not exceed
ADA maximum grade requirements.
Local Roads
Grades for local residential streets should be as level as practical, consistent with the
surrounding terrain. The gradient for local urban streets should be less than 15%. Where
grades of 4% or steeper are necessary, the drainage design shall be the critical governing
design parameter. On such grades special care should be taken to prevent erosion on slopes
of roadside ditches and earthen/grass lined open drainage facilities. For streets in
commercial and industrial areas, grades should be less than 5% and flatter grades are
encouraged.
6.3.4 Vertical curves shall be designed when algebraic difference in grade
exceeds 1 %. Elevations shall be shown on the construction plans at a
minimum of 10 foot horizontal intervals through vertical curves. The
gradient for tangents to vertical curves at railroad crossings shall be a
maximum of 3.5%. All crest vertical curves shall be determined by sight
distance requirements for the design speed. The minimum design speed
on any vertical curve shall be based on roadway classification.
6.3.5 Intersections and curves shall be evaluated for adequate sight stopping
distances based on the design speed.
A. Minimum stopping sight distances shall conform to the following
design standards:
a. The driver's eye height shall be assumed to be 3.5 feet above
the finished pavement.
b. The height of the object seen by the driver shall be assumed
to be 2.0 feet.
c. A deceleration rate of 11.2 feet/s2 shall be used.
d. A brake reaction time of 2.5 seconds shall be used.
Page 4 of 15 Roadway Design Critena
Thoroughfares
30
1
35
Design
40l
Speeds m h
45 50
55
60
pe of Terrain
Maximum
Gra es (%+
Level
_
8
1
7
1
7
6 1 6
1
5
1
5
Table 6.4
Collectors
Type of Terrain
Level
Design Speeds (mph)
20 1 25 1 30 1 35 1 40 1 _45 )50 1 55 1 60
Maximum Grades (%)(I)
9 1 9 1 9 1 9 )9 1 8 I 7 ) 7 I 6
(1) Short lengths of grade in urban areas, such as grades less than 500 ft in length, one-
way downgrades, and grades on low-volume urban collectors may be up to 2% steeper
than the grades shown above. Note: Sidewalks along these roadways shall not exceed
ADA maximum grade requirements.
Local Roads
Grades for local residential streets should be as level as practical, consistent with the
surrounding terrain. The gradient for local urban streets should be less than 15%. Where
grades of 4% or steeper are necessary, the drainage design shall be the critical governing
design parameter. On such grades special care should be taken to prevent erosion on slopes
of roadside ditches and earthen/grass lined open drainage facilities. For streets in
commercial and industrial areas, grades should be less than 5% and flatter grades are
encouraged.
6.3.4 Vertical curves shall be designed when algebraic difference in grade
exceeds 1 %. Elevations shall be shown on the construction plans at a
minimum of 10 foot horizontal intervals through vertical curves. The
gradient for tangents to vertical curves at railroad crossings shall be a
maximum of 3.5%. All crest vertical curves shall be determined by sight
distance requirements for the design speed. The minimum design speed
on any vertical curve shall be based on roadway classification.
6.3.5 Intersections and curves shall be evaluated for adequate sight stopping
distances based on the design speed.
A. Minimum stopping sight distances shall conform to the following
design standards:
a. The driver's eye height shall be assumed to be 3.5 feet above
the finished pavement.
b. The height of the object seen by the driver shall be assumed
to be 2.0 feet.
c. A deceleration rate of 11.2 feet/s2 shall be used.
d. A brake reaction time of 2.5 seconds shall be used.
Page 4 of 15 Roadway Design Critena
e. Minimum sight stopping distances shall be adjusted by the
Professional Engineer of Record, when there is a presence of
vertical curves within the distance needed for stopping as
recommended by AASHTO's A Policy on Geometric Design
of Highways and Streets where applicable.
B. Open space clips shall be established at all intersections. Unless
larger clips are required at a particular intersection, a minimum 10 -
foot x 10 -foot triangular open space corner clip for zoned residential
areas, as measured from the projected property line, is required at
the intersection of two streets. At intersection of collector streets or
greater, minimum 25 -foot x 25 -foot open space corner clip or larger,
as design requires, shall be provided. Such clips shall be part of the
public right-of-way and may not be located on private property.
C. Major and secondary thoroughfares with a centerline radius of the
right-of-way less than 2000 feet shall be designed in accordance
with the guidelines for superelevation as specified in the AASHTO
A Policy on Geometric Design of Highways and Streets. Signage
and design speed shall be accounted for in all curved thoroughfares.
The maximum rate of superelevation shall be 0.06 for urban
conditions. Streets with a centerline radius of over 2000 feet are not
required to have superelevation.
D. Collector and local streets horizontal curves may be designed
without superelevation.
E. Minimum Horizontal Curve Radii Lengths:
a. Major Thoroughfares: 2000 feet.
b. Secondary Thoroughfares: 2000 feet.
c. Major Collector Streets: 850 feet
d. Minor Collector Streets: 850 feet.
e. Local Residential Streets: 450 feet.
For radii less than above, designer must receive specific approval
from the office of the City Engineer.
6.3.6 For the purposes of these design standards, tangent length is defined as the
distance between the point of tangency and the point of curvature of two
adjacent curves along the centerline of the street right-of-way.
A. The minimum tangent length between reverse curves shall be 100
feet on principal arterials, minor arterials, major collector streets,
and minor collector streets.
B. The minimum tangent length between reverse curves shall be 50 feet
on all local streets.
6.3.7 Intersections
Page 5 of 15 Roadway Design Cntena
A. Curb radii, measured from the face of curb, shall be 35 feet
minimum on major and secondary thoroughfares. The minimum
curb radius shall be 25 feet on collector and local streets. Skewed
intersections shall be designed with larger radius.
B. Streets and traffic lanes should be aligned across an intersection.
Except where existing conditions will not permit, all streets should
intersect at a 90 degree angle. The maximum allowable skew across
an intersection shall be 5 degrees for arterial streets, and 10 degrees
on all collector and local streets.
C. When turnouts are provided at an existing street, the ultimate cross
section is required to the end of the curb return. Pavement transition
is required to reduce the pavement width to the existing cross
section.
D. Taper rates for adding or dropping a lane shall be at a minimum of
straight line tapers with a minimum of an 8:1 rate for design speeds
up to 30 mph and 15:1 for design speeds up to 50 mph. For design
speeds over 50 mph the Professional Engineer of Record shall
submit a design providing adequate taper lengths appropriate for the
corresponding design speed. The use of partial tangent tapers,
symmetrical reverse curves, and asymmetrical reverse curves are
encouraged and should be designed to fit the design speed of the
design road but are not required.
E. Right -of -Way corner clips are required for all Thoroughfare
roadways. Triangular corner clips shall be a minimum of 25 -foot x
25 -foot.
F. Collector and local roadways shall have a 25 ft. radius for the right-
of-way at all intersections.
6.3.8 Minimum lane transition lengths shall meet or exceed requirements of the
A Policy on Geometric Design of Highways and Streets. Pavement width
transitions shall conform to the following design standards:
A. Minimum deceleration lengths for auxiliary turning lanes on grades
of less than or equal to 3%, with an accompanying stop condition,
for design speeds of 30, 40, 45, 50, 55 mph are 230, 330, 430, 550
and 680 feet respectively. These lengths exclude the taper lengths.
B. Taper lengths should be calculated for roads with design speeds
greater than or equal to 45 mph by using taper lengths (L) equal to
0.6 times the design speed (S) multiplied by the offset (W),
L=0.6SW. For design speeds less than 45 mph, the taper length (L)
equals the offset multiplied by the design speed(s) squared, then
divided by 155, L=WS2/155. The distance for tapers should be
lengthened if the road is curved based on recommendations from the
Professional Engineer of Record.
Page 6 of 15 Roadway Design Catena
6.3.9 Left Turn Lanes
A. Minimum storage bay length shall be 100' for collector streets and
150' for thoroughfare streets. Longer storage bay lengths may be
required based on the results of a Traffic Impact Analysis.
B. Mid -block left turn lanes may be allowed if a Traffic Impact
Analysis and the office of the City Engineer recommends their use
in relation to a proposed development. Left turn lanes shall be
provided at the intersection of public street rights-of-way.
C. Minimum transition taper length with 500' Radius shall be 180' for
Collector streets and 200' for thoroughfares.
D. The office of the City Engineer reserves the right to require that a
Traffic Impact Analysis be submitted for any proposed
development.
E. Left -turn lane width shall be a minimum of 12 ft.
6.3.10 On major and secondary thoroughfares esplanade openings may be spaced
a minimum of 600 feet apart. Median openings shall conform to the
following design standards:
A. For median openings including left turn lanes, the storage and taper
lengths mentioned in these design criteria shall apply.
B. The median opening at the intersection of two streets shall be at least
the width of the minor right-of-way plus 10 feet. These median
openings may be wider based on lane configurations or traffic
volumes. In such cases sufficient traffic analysis and data should be
presented along with design.
C. Variations to these criteria may be granted on a case by case basis
by the office of the City Engineer .
6.3.11 Cul-de-sac Pavement
A. Residential minimum pavement radii for the cul-de-sac bulb as
measured to the face of curb shall be 40 feet.
B. Commercial and industrial minimum pavement radii for the cul-de-
sac bulb as measured to the face of curb shall be 45 feet.
C. Right-of-way radius shall be clear of permanent obstructions.
D. Curb radii at the transition to the cul-de-sac shall have a typical
radius of 25 feet in single family residential areas and 35 feet in all
other areas as measured at the face of curb.
E. The length of a cul-de-sac is defined as the distance from the
centerline of the intersecting pavement to the center of the cul-de-
sac bulb measured along the centerline of the street right-of-way.
Maximum length of cul-de-sac local streets for residential
subdivisions shall be 600 feet. Dead end collectors and dead-end
major and minor thoroughfares shall not be allowed.
Page 7 of 15 Roadway Design Cnteria
F. The office of the City Engineer reserves the right to require shorter
maximum lengths of commercial and industrial cul-de-sacs or dead-
end streets where high traffic volumes are present.
6.3.12 The design of on street parking shall conform to the following design criteria:
A. All on -street parking shall be parallel parking only.
B. On -street parking spaces shall be striped with white paint.
C. The width of on -street parking spaces shall be a minimum of 8 feet
in width as measured from the inside of the painted stripe to the face
of curb when allowed or approved by special design and with study
by and consultation with the Planning Department.
6.4 PAVEMENT STRUCTURE REQUIREMENTS
6.4.1 The pavement structure for all roadways outside of zoned industrial areas
shall be designed based on soil data from the site and geotechnical analysis,
anticipated traffic volume, desired service life of the proposed pavement.
The Professional Engineer of Record is responsible for ensuring that the
pavement structure is designed to withstand the anticipated loads that are
expected on the roadway. All roadways outside of zoned industrial areas
shall be designed to adequately handle the design vehicle weight. Such
criteria shall be used to design the roadway when these data, in sum,
recommend a pavement larger than the minimums below.
6.4.2 For the typical pavement section and detail for local residential streets,
minor collectors, major collectors, secondary and major thoroughfares,
refer to City's Standard Construction Details.
6.4.3 For the pavement structure for all public roadways inside zoned industrial
districts, the concrete pavement design and the calculation of its thickness
shall be based on AASHTO design procedures for rigid pavements and
shall be based on independent studies of projected truck traffic, projected
passenger vehicle traffic, geotechnical investigations, anticipated vehicle
loading by design vehicle and with consultation with the Planning
Department. Prior to any pavement design the developer shall consult with
the office of the City Engineer .
6.4.4 The use of rebar dowels or the use of saw -cutting procedures to expose
existing steel in concrete pavement is required to create a minimum of 12
inches of overlap of reinforcing steel when making a connection of a
proposed concrete street to an existing concrete street or road. When the
existing street has no exposed steel the following shall apply:
A. Dowels should be No. 4 rebar, 24 inches long, embedded 12 inches
and epoxied into the existing concrete. Applicable spacings shall be
the same as the rebar spacings mentioned in these design criteria for
the various concrete thicknesses.
Page 8 of 15 Roadway Design Critena
6.4.5 Dead-end streets and concrete paved streets designed to be extended in the
future shall have paving headers and 15 inches of reinforcing steel exposed
beyond the pavement (coated with asphalt and wrapped with burlap), or
dowel type expansion joint for future pavement tie-in.
6.4.6 Pavement extensions shall connect to the existing pavement with a
pavement undercut and a minimum steel overlap of 12 inches.
6.4.7 All concrete paving to be removed shall be removed to either an existing
joint or a saw -cut joint. Sawed joints shall meet the requirements set out
in this section. If utilizing epoxied rebar dowels is difficult, not possible
or where existing conditions prohibit the use of dowels, saw -cut to a
minimum depth of 2 inches and remove existing concrete to expose a
minimum of 12 inches of longitudinal steel, in good condition, with an
equivalent cross-sectional area of steel equal to the proposed pavement
steel. Tie this exposed steel to the new steel in the proposed street and pour
the new concrete over both.
6.4.8 Materials — For all pavement materials, refer to the City's Standard
Specifications.
6.5 GRADING AND LAYOUT REQUIREMENTS
6.5.1 Minimum gradient on any gutter shall be 0.30%.
6.5.2 See Chapter 5 of the Engineering Design Criteria Manual (EDCM) for inlet
spacing.
6.5.3 The maximum allowable slope for driveways shall be in accordance with
the City's Standard Construction Details.
6.5.4 The algebraic sum of grades to an inlet at an intersection should not exceed
1%.
6.5.5 All new residential and local streets poured with a curb and gutter
arrangement shall have a minimum of a 4 inch rollover, lay down curb or
approved equal. All new collector and thoroughfare streets poured with a
curb and gutter arrangement shall have the standard 6 inch stand up type
curb. A standard 6 inch curb shall be used immediately adjacent to all
storm sewer inlets; where necessary 4 inch rollover curbs shall be
transitioned to a 6 inch curb at the inlet.
6.5.6 The minimum grade line around a cul-de-sac shall be 0.70%.
6.5.7 The amount of cross slope over the pavement section shall be 2% sloping
away from the crown of road or centerline.
6.5.8 When connecting to an existing curbed street, the gutter lines for the
proposed and existing streets shall be matched.
6.5.9 Proposed top of curb elevations should be designed to match the top of the
curb at an existing street in cases where a proposed street is being
connected to an existing street.
6.5.10 Top of curb elevations shall be shown on the construction plans along with
a detail of the type of curb used.
Page 9 of 15 Roadway Design Critena
6.5.11 Gutter line elevations for vertical curves shall be shown on the construction
drawings in cases where a railroad track is being crossed. Where railroad
crossings are not at right angles to the pavement, vertical curves should be
calculated for each curb line and should be posted at 10 foot intervals of
the centerline of the road on the construction drawings in both plan and
profile view. The grade of the railroad track shall be matched with the
centerline of the road at the intersection of the crossing.
6.5.12 All Major and Secondary Thoroughfares shall be designed so that, at all
valley locations, ponding water from the 1 00 -year rainfall events does not
exceed 3 -inches of depth along the gutter line of inside curb. This
condition is described as "one lane passable".
6.6 TRAFFIC CONTROL DEVICES
6.6.1 Standard Type III barricades shall be permanently installed by the
developer at the end of all dead-end streets not terminating in a cul-de-sac,
and at all turnouts. These barricades shall meet at least the minimum
requirements of the TMUTCD. The erection of these Type III barricades
shall not preclude the installation of other decorative fencing or
landscaping behind the barricade for the purposes of maintaining private
property, safety, aesthetics etc. .
6.6.2 Traffic signage locations, street signage locations, and pavement markings
shall be shown on the paving overall layout in the construction drawings.
The construction drawings should include pavement marking details where
applicable.
6.6.3 Pavement markings shall be shown on the final construction plans for a
project. Reflectorized paint with supplemental reflectors, or approved
equal, shall be used on all major thoroughfares and on major collector
streets. Turn lanes shall have proper pavement markings. All pavement
markings shall conform to the latest edition of TMUTCD .
6.6.4 A blue reflectorized raised pavement marker or button is required at all fire
hydrants and shall be located 6 inches off the pavement centerline toward
the fire hydrant.
6.6.5 The developer shall install requisite traffic control devices when a signal
is warranted by a traffic study.
6.7 SIDEWALKS
6.7.1 Sidewalks meeting Americans with Disabilities Act (ADA) and Texas
Accessibility Standards (TAS) parameters are required on each side of all
public streets. The developer shall be responsible for the installation of all
sidewalks in a new development in residential or other areas as required.
This shall include but not be limited to along parks, drainage channels,
public utility easements, pipeline easements and detention ponds.
Page 10 of 15 Roadway Design C ntena
Sidewalk width and location shall be in accordance with the City's
Standard Construction Details. The developer is responsible for obtaining
any and all agreements with the public utilities for the installation of
sidewalks across applicable easements.
6.7.2 Sidewalk wheelchair ramps shall be required at all intersections and 90
degree bends in the street and shall adhere to ADA design criteria.
6.7.3 Sidewalk construction in an esplanade shall be at the esplanade noses only
and shall conform to the following parameters: A transverse concrete
sidewalk, 6 inches thick, shall be constructed in all esplanades as a
pedestrian refuge area. All concrete sidewalks in esplanades shall be 6-10
feet wide as measured from the esplanade nose. Patterned concrete or brick
stamp may be used. Any ramps associated with sidewalks in an esplanade
shall conform to ADA design criteria.
6.7.4 Sidewalk Construction shall be in accordance with the City's Standard
Construction Details.
6.7.5 Specialty sidewalks such as brick sidewalks or other non-standard
sidewalk material must receive special approval from the office of the City
Engineer.
6.8 DRIVEWAYS
6.8.1 It is desirable to minimize the number of driveways on all thoroughfares
and collect streets in order to reduce the number of conflict points and
facilitate traffic flow. It is recognized, however, that certain existing tracts
may not be able to fully comply with the following standards due to limited
frontage and other constraints. When compliance with these criteria is
precluded due to the location of driveways on adjoining properties,
attempts should be made to obtain alternative access where feasible,
including joint access driveways, access easements to adjoining properties
or access to intersecting streets.
6.8.2 Non-residential driveways shall be twenty-five feet (25') to thirty-five feet
(35') wide. On roadways classified as a major collector or greater, non-
residential driveways shall be thirty-five feet (35') wide unless specifically
approved by the office of the City Engineer.
6.8.3 Non-residential driveways shall be placed no closer (the minimum
separation) than the following distances from adjacent streets and
driveways, unless specifically approved by the office of the City Engineer.
Roadway Classification
(As indicated on Thoroughfare Plan)
Major Thoroughfares
Secondary Thoroughfares
Major Collectors
Minimum Separation
350'
250'
200'
Page 1 1 of 15 Roadway Design Critena
Minor Collectors 165'
Local Streets 75'
The driveway separation distance is measured from the projected curb line
of the intersecting street or drive to the nearest projected curb line of the
proposed driveway.
6.8.4 In order to implement the driveway separation, shared access on all non-
residential driveways shall be required between adjacent properties.
6.8.5 On collector streets and above, without medians, non-residential driveways
shall maintain alignment with opposing driveways or meet minimum
separation stated in 7.2.3, unless specifically approved by the office of the
City Engineer.
6.8.6 Alignment of driveways with opposing streets is discouraged for
signalized intersections unless specifically approved by the office of the
City Engineer. When such a design is approved, the driveway widths shall
be increased to match the cross-section of the opposing street.
6.8.7 Non-residential driveway connections to the public street shall be approved
and inspected by the City of Pearland.
6.8.8 Single access driveway radii shall not extend beyond the projection of a
property corner to the back of curb.
6.8.9 Driveways shall be installed in accordance with the City of Pearland
standards.
6.8.10 Driveways shall be evaluated with respect to signage, landscaping and
structures for adequate sight distances.
6.8.11 Non-residential minimum driveway radii accessing a secondary
thoroughfare or greater shall have a radii of 35 feet. Radii for non-
residential driveways on other roadways shall be minimum 25 feet.
6.8.12 Single-family residential driveways shall be a minimum of ten feet (10')
wide at the right-of-way line.
6.8.13 Single-family residential driveways shall not be allowed on roadways
classified as major collector or greater unless the lot has 100' of frontage
or greater. In these situations a circular driveway shall be required.
6.8.14 Driveways connecting to the Texas Department of Transportation
(TxDOT) roadways will require City approval and a TxDOT permit. The
TxDOT permit application shall be completed by the landowner and
submitted to the office of the City Engineer for approval and forwarding
to TxDOT. The permit will be sent to the applicant by TxDOT upon
completion.
6.8.15 Driveway grades shall be minimized as much as possible. The maximum
algebraic change in grade between driveway and street is 7%.
Page 12 of 15 Roadway Design Catena
6.9 TRAILS
6.9.1 Trails are a specific feature that must accommodate multiple non -motorized
use (pedestrian and bicycle).
6.9.2 Trail construction must comply with all applicable Municipal, State and
Federal regulations to include TAS and ADA.
6.9.3 Trails not meeting the Design Standards will not count towards Parkland
Dedication requirements.
6.9.4 Trails in utility corridors require the written consent of the corresponding
utility company, and the approval of the office of the City Engineer at the
time of subdivision application.
6.9.5 Removable barrier(s) will be provided to prevent unauthorized vehicular
access on to trail.
6.9.6 Bollards or operable guard rails are acceptable as removable barriers.
Bollards are to be set at 4 foot on center, on the width of the pedestrian right-
of-way.
6.9.7 Provide Trail Rule signage, pedestrian caution signage, and no motorized
vehicle warning signage where trail intersects with public roadways.
Provide signage submittal with color rendering for the office of City
Engineer approval.
6.9.8 Trails along street rights-of-way shall be a minimum of 8 feet wide and
constructed of concrete, or pervious concrete/materials (if approved by the
office of the City Engineer). The City may elect to contribute to the cost of
the trail if a width wider than 8 feet is deemed appropriate for that specific
location.
6.9.9 Concrete curb on roadway to be standard 6 -inch concrete curb and gutter
along street frontage that abuts trail right-of-way.
6.9.10 Trails in the street rights-of-way shall include landscaping (trees and
shrubs) on each side of the trail for the remaining area of parkway, from the
back of the curb to the right-of-way line. Landscaped areas to have a
minimum depth of 4 inches of screening material over non -woven
polypropylene weed barrier pinned every 12 inches on center along
overlapped edges and seams, and every 2 feet on center in field.
6.9.11 Trails within parkland shall be constructed of concrete, except as indicated
below:
A. Proposals for alternative surface trails in parkland and areas not
designated as "Natural Open Space" may be submitted through the
Alternative Design Process and require the approval of the office of
City Engineer prior to subdivision approval.
6.9.12 Landscaping (trees and shrubs) shall be provided at a minimum of 5 feet
wide along each side of the trail.
6.9.13 Install shrubs at a minimum spacing of 7 feet apart and provide drip
irrigation.
6.9.14 Shade trees shall be spaced a minimum of 20 feet apart and be planted 5 —
7 feet from the trail. Trees shall have a drip irrigation system provided.
Page 13 of 15 Roadway Design Cnteria
Tree species shall be consistent with the street tree requirement as
referenced on the approved tree list for the City.
6.9.15 Minimum of one park bench shall be provided for each section of the trail
or spaced at a minimum 600 feet apart. Park bench must have concrete
pad to ensure compliance with accessibility requirement for companion
seating.
6.9.16 Concrete trail shall be minimum 10 feet wide with minimum 6 inches
thick, reinforced with #4 rebars on 12" spacing, continuous each way, on 8
inches of sub -grade to be scarified and compacted to minimum 95%
density per ASTM D —1557. Concrete shall have minimum 3,000 psi
strength as specified in standard specification. Surface shall be rough
broom finish. Cross -slope shall not exceed 1%, sloped into park.
Expansion joint must be provided along back of concrete curb and be
provided with 0.5 inch expansion joint material. Control joints shall be
0.25 inch wide. The depth of the control joint shall be 25% of the thickness
of the slab. Control joints to be placed every 10 feet on center. Expansion
Cold joint every twenty feet with 0.5 inch thick expansion joint material.
Running slope of trail may not exceed five percent (5%) in any direction.
6.9.17 Trails in natural open space areas shall remain undisturbed except for trail
corridors, as approved by the office of City Engineer. Use of concrete
and/or asphalt is prohibited in natural open space areas. In the event that
natural open space is disturbed outside of the designated trail corridor,
Office of City Engineer must be immediately notified and an inspection
will be conducted to determine the appropriate remedy. The design,
surface and treatment of trails in natural open space areas require the
approval of office of City Engineer prior to subdivision approval. In
natural open space areas, additional signage advising users to stay within
the designated trail corridor is required.
6.9.18 Trail surfaces in non right-of-way areas can be concrete or asphalt with
concrete header curbs, meeting following requirements:
A. Concrete trail shall be minimum 10 feet wide with minimum 6 inches
thick reinforced with #4 rebars on 12" spacing, continuous each way,
on 8 inches of sub -grade to be scarified and compacted to minimum
95% density per ASTM D —1557. Concrete shall have minimum
3,000 psi strength as specified in standard specification. Surface shall
be rough broom finish. Cross -slope shall not exceed 1%, sloped into
park. Expansion joint must be provided along back of concrete curb
and be provided with 0.5 inch expansion joint material. Control joints
shall be 0.25 inch wide. The depth of the control joint shall be 25% of
the thickness of the slab. Control joints to be placed every 10 feet on
center. Expansion Cold joint every twenty feet with 0.5 inch thick
expansion joint material. Running slope of trail may not exceed five
percent (5%) in any direction.
B. Asphalt trail shall be 10 feet wide plus (2) 6 inch concrete header
curbs, for an overall width of 11 feet. Asphalt pavement shall be a
minimum of 1.5 inches thick, Type "D" HMAC, City of Pearland
Pagc 14 of 15 Roadway Design Criteria
standards, seal coated (2 coats), compacted to 98% minimum density
as per ASTM D-1557. Pavement structure shall be placed over a
minimum 4.5 inches of 2 sacks per cubic yard cement stabilized base
course material compacted at 100% density as per ASTM D-1557 and
minimum 8 inches scarified sub -grade compacted at 95% minimum
density as per ASTM D-1557. Header curbs shall be 3,000 psi
concrete strength with 2 continuous #4 rebars. Provide'' Y2 inch
expansion joints every 20 feet and control joints every 5 feet. Provide
a broom finish.
C. Alternative trail surface proposals require the approval of the office of
the City Engineer prior to subdivision approval. Trail must be
stabilized with 2 sacks of cement per cubic yard, and shall comply
with all applicable TAS and ADA standards. Alternative Surfaces
may include earthen; organic or inorganic material, such as mulch,
chat, gravel, or hardscape; permeable pavement or other
environmentally. friendly material.
Page 15 of 15 Roadway Design Cnteria
CITY OF PEARLAND
CHAPTER 7
TRAFFIC DESIGN CRITERIA
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
1 of 8 Traffic Design Criteria
CHAPTER 7
TRAFFIC DESIGN CRITERIA
7.1 Traffic Impact Analysis (TIA)
7.1.1 Purpose
The City requires a TIA be performed if it is determined that a proposed site
development is expected to have an impact on operation of a City street or
State road within the City limits. Such studies are necessary to define the
possible magnitude of impact(s) of the proposed development on traffic
operation of affected streets. The City may require any and all public
improvements, or a proportionate share, as recommended by the TIA be
implemented to provide accommodation of the traffic generated by the
proposed development. These guidelines detail the procedures to be
utilized when conducting a TIA for a proposed site development. These
guidelines have been developed to ensure that the TIA will include the
necessary information in a format that allows the office of City Engineer to
review and make informed comments and decisions in a timely manner.
Before any work is performed on the TIA, it is required that the applicant
meet with the office of the City Engineer to determine the scope of
requirements for the TIA. Items to be agreed to include, but not limited to,
study area and intersections, applicable standards and methodologies,
ultimate analysis year, growth rate methodologies, nearby proposed
developments to be accounted for, etc.
7.1.2 Determining the Need for a Traffic Impact Analysis
A Traffic Impact Analysis is conducted to enable the City to identify the
potential impacts of a proposed development and determine any roadway
improvements necessary to provide an acceptable level of service. The
TIA should be conducted during the initial stages of the site development
review and approval process in order to adequately consider the impacts the
development will have on the City's transportation network.
Not all developments will have a significant enough impact to require a
TIA. The use of engineering judgment is necessary in making this
determination and consideration should be given not only to changes in
projected traffic volumes but also safety and capacity deficiencies which
could impact the highway system. At a minimum, a TIA shall be performed
when any of the following conditions are satisfied:
A. The proposed development is expected to generate 1,000 or more
vehicle trips per day (total inbound and outbound development traffic.)
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B. The proposed development is expected to generate 50 or more vehicle
trips during a peak hour of the adjacent roadway.
C. Development is 100 acres or larger. This acreage is inclusive of all
right-of-ways, reserves, and easements.
D. Zoning or rezoning requests.
E. Amendment to City Thoroughfare Plan.
F. When required by the office of the City Engineer.
In order to assist City in determining whether a TIA should be performed,
the applicant must fill out a Trip Generation Worksheet. This worksheet
must be submitted with each plat and/or site plan for developments that do
not have an approved TIA. This worksheet must be filled out using the latest
edition of the Institute of Transportation Engineers Trip Generation Manual.
If the development land use is not known at the time of the submittal then
the applicant should make assumption based on the worst-case scenario for
the site. Should this be the case, at a minimum, designer should evaluate
the type of land use allowed by the city's zoning ordinance criteria, the
maximum amount of developable land taking into account setbacks and
other restrictions such as detention, easement, etc., logical assumptions by
the designer, and adjacent land uses. If the proposed land use is not listed in
the Trip Generation Manual, the City shall require a letter from a Texas
registered professional engineer, in lieu of the trip generation worksheet,
documenting the type of development proposed and identify the number of
trips generated based on either a trip generation study performed for a similar
land use or designer's professional opinion if such report is not available.
This letter report must be signed and sealed by a registered professional
engineer in the State of Texas.
7.1.3 A Traffic Impact Analysis report shall include, at a minimum, the following
information:
A. An executive summary,
B. Study purpose and objectives,
C. Description of the proposed development and study area,
D. Existing conditions in the area of the development,
E. Recorded or approved nearby development
F. Trip generation and trip distribution,
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G. Projected future traffic volumes,
H. An assessment of the change in roadway operating conditions
resulting from the development traffic,
I. Recommendations for site access and transportation improvements
needed to maintain traffic flow to, from, within, and past the site at
an acceptable and safe level of service.
J. Exhibits to show all existing, proposed and future facilities on the
site, all proposed traffic movements, and all existing, generated,
future background and proposed traffic volumes within the existing
and proposed street network
K. Appendices to include detailed site plan, existing 24-hour
directional counts, existing AM & PM peak hour turning movement
counts, all Synchro (or similar software ) report, traffic signal
warrant analysis, and CD containing Synchro (or similar software)
files, and any other pertinent information.
Prior to preparation of a Traffic Impact Analysis report, the design engineer
is to meet with the office of the City Engineer to identify the study area,
define the area of influence, and non -site traffic impacts.
7.1.4 The analysis shall be presented in a straightforward and logical sequence.
It shall lead the reader step-by-step through the various stages of the process
and resulting conclusions and recommendations. The analysis shall be
presented in a manner that allows the reviewer to easily duplicate the
calculations. The recommendations shall specify the time period within
which the improvements should be made, particularly if the improvements
are associated with various phases of the development construction. The
recommendations shall also specify the time period for any required
monitoring of operating conditions. Data shall be presented in tables,
graphs, maps, and diagrams wherever possible for clarity and ease of
review. An executive summary of one or two pages shall be provided,
concisely summarizing the purpose, conclusions, and recommendations.
The Traffic Impact Analysis report shall conform with the following
process of analysis:
A. Preparer — The report shall be prepared under the supervision of a
qualified and experienced transportation engineer with specific
training in traffic and transportation engineering and at least two (2)
years of experience related to preparing Traffic Impact Analysis
reports. A professional engineer, registered in the state of Texas,
shall seal the report.
B. Study Area - The study area shall be based on the characteristics of
the surrounding area. The office of the City Engineer and the traffic
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engineer preparing the study shall mutually agree upon the
intersections.
C. Design Year — The traffic forecasts shall be prepared for the
anticipated opening year of the development, assuming full build-
out and occupancy. This year is referred to as the "Design Year". If
development is phased, provide forecast for each phase of the
development.
D. Trip Generation Rates — The Traffic Impact Analysis report shall
include a table showing the categories and quantities of land uses,
with the corresponding trip generation rates or equations, and
resulting number of trips. The trip generation rates used must be
either from the latest edition of "Trip Generation Manual" (Institute
of Transportation Engineers (ITE), Washington, D.C.) or from a
local study of corresponding land uses and quantities and approved
by the office of City Engineer. All sources must be referenced in
the study and calculations must be documented and included in the
study report.
E. Pass -by and/or Shared Trips — If pass -by or shared trips are a major
consideration for the land use in question, studies and interviews at
similar land uses must be conducted or referenced. Any significant
difference between the sums of single -use rates and proposed
mixed-use estimates must be justified in the report. Pass -by trips
and/or shared trips shall be shown separately and clearly in diagram
form at each driveway and intersection affected. Designer to follow
ITE Trip Generation Handbook or regional Metropolitan Planning
Organization studies from similar land uses.
F. Non -Site Traffic Estimates — Estimates of non -site traffic shall be
made, and will consist of through traffic and traffic generated by all
other developments within the study area for which preliminary
estimated or fmal plans have been approved. Non -site traffic may
be estimated using trends or growth rates, approved by the City
traffic engineer.
G. Estimates of Trip Distribution — Trip distribution shall be estimated
for the site design year and shown separately and clearly using
diagrams. A multi -use development may require more than one
distribution and coinciding assignments for each phase.
Consideration must also be given to whether inbound and outbound
trips will have similar distributions.
H. Trip Assignments — Assignments must be made considering logical
routings, available roadways capacities, left turns at critical
intersections, and projected (and perceived) minimum travel times.
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In addition, multiple paths should often be assigned between origins
and destinations to achieve realistic estimates rather than assigning
all of the trips to the route with the shortest travel time. The
assignments must be carried through the external site access points
and in large projects through the internal roadways. When the site
has more than one access driveway, logical routing and possibly
multiple paths should be used to obtain realistic driveway volumes.
The assignment should reflect conditions for the time period being
analyzed.
If a thorough analysis is required to account for pass -by trips, the
following procedure should be used:
1. Determine the percentage of pass -by trips in the total trips
generated.
2. Estimate a trip distribution for the pass -by trips.
3. Perform two separate trip assignments, based on the new and
pass -by trip distributions, and
4. Continue the pass -by and new trip assignments.
Upon completion of the initial site traffic assignment, the results
should be reviewed to see if the volumes appear logical given
characteristics of the road system and trip distribution. Adjustments
should be made if the initial results do not appear to be logical or
reasonable.
Total Traffic Impacts — Traffic estimates for any site with current
traffic activity must reflect not only new traffic associated with the
site's development, but also the trips subtracted from the traffic
stream because of the removal of an existing land use. The traffic
impact report should clearly depict the total traffic estimate and each
of its components.
J. Capacity Analysis — Capacity analysis must be performed at each of
the major streets and project site access intersection locations,
signalized and unsignalized, within the study area. Signalized
intersections in coordinated systems must be analyzed as a system.
In addition, analysis must be completed for roadway segments,
deemed sensitive to site traffic within the study area. These may
include such segments as weaving section, ramps, internal site
roadways, parking facility access points, and reservoirs for vehicles
queuing off-site and on-site. Other locations may be deemed
appropriate depending on the situation.
6 of 8 Traffic Design Criteria
The operational analysis and methodology in the current version of
the "Highway Capacity Manual, Special Report 209"
(Transportation Research Board, National Research Council,
Washington, D.C.) should be used for analyzing existing conditions,
traffic impacts, access requirements, or other future conditions for
which traffic, geometric and control parameters can be established.
K. Internal Site Review — A review of the site shall be made and must
include traffic circulation, pedestrian accommodations, vehicle
storage requirements and any other traffic concerns.
L. Required Levels of Service — The recommendations of the traffic
impact shall provide safe and efficient movement of traffic to and
from and within and past the proposed development, while
minimizing the impact to non -site trips. The current levels of
service must:
1. Be maintained if they are "C" or less, and
2. Not deteriorate to worse than "C" if they are currently "A" or
M. Intersection Geometry — Analysis shall include a thorough
evaluation of intersection geometry at affected driveways and
intersections to determine the need for and required length of turn
lanes.
N. Pedestrians and Bicycles - As warranted, TIA must consider and
provide adequate and safe facilities for pedestrians, bicyclists, and
those with disabilities, to ensure that internal circulation system and
extemal access points designed to minimize conflicts with vehicular
traffic. Pedestrian circulation should be comprehensive and provide
connections between buildings, and from all streets, and signals into
the site.
0. Schools — For sites where schools are proposed, site specific
analysis of school site plan must be performed as part of the TIA to
consider and provide a safe route to school plan, crossing locations,
necessary traffic control, traffic calming devices if necessary,
driveway locations, pedestrian and bicycle circulation, on-site drop
off/pick-up area with adequate queuing to avoid back-ups onto
public streets, and bus circulation.
P. Speed Zone - If TIA recommends designation of a school zone, a
Speed Zone study and report must be performed to define the
required speeds and the installation of appropriate signage. This
report must be signed and sealed by a registered professional
engineer in the State of Texas.
7 of 8 Traffic Design Criteria
Q.
Traffic Signal Warrant Analysis — Traffic signal warrant analyses
must be performed based on the procedure outlined in the latest
edition of the Texas Manual on Uniform Traffic Control Devices.
R. Roundabouts - If a roundabout and/or other traffic calming features
are proposed as part of the development, the TIA must present
justifications for such installation. Design of roundabout must be in
accordance with requirements of Chapter 6 and the latest edition of
AASHTO's "A Policy on Geometric Design of Highways and
Streets".
S. Service and Delivery Vehicles - As warranted, TIA must consider
and provide adequate facilities and circulation for the movement of
service and delivery vehicles to and from the site. Of particular
interest is that adequate turning paths are provided for large service
vehicles to allow entry and exit without encroaching upon opposing
lanes or curbed areas. In addition, sufficient storage areas and
loading zones must be provided to avoid parking and circulation
routes issues for other vehicles.
T. Responsibility for Improvements — The report shall include a list of
required improvements, the anticipated date the improvement will
be required, and a cost estimate for each recommended
improvement. The applicant shall be responsible for the
improvements required to provide safe and convenient ingress and
egress to the development site.
U. Report Approval — Approval of a specific development is contingent
upon approval of the traffic impact analysis and agreement by the
office of the City Engineer on required improvements.
8 of 8 Traffic Design Criteria
CITY OF PEARLAND
CHAPTER 8
STORMWATER MANAGEMENT
FINAL DRAFT REVISIONS (September 2016)
ENGINEERING DESIGN CRITERIA MANUAL
September 2016
Page 1 of 13 Stormwater Management
CHAPTER 8
STORMWATER MANAGEMENT
8.1 GENERAL
The City of Pearland is a Small Municipal Separate Storm Sewer System (MS4)
operator since 2008 under TPDES Phase II MS4 General Permit. Based on census
data of 2010, the City is a level III MS4 operator. This chapter provides design
guidelines to improve the Stormwater Quality through the implementation of certain
Best Management Practices (BMPs). Use of BMPs presented here does not
guarantee acceptance of a particular Storm Water Pollution Prevention Plan (SW3P)
or the effectiveness of the BMP to reduce pollutant. The SWP3 and BMPs shall be
prepared and designed in accordance with TCEQ and other regulatory guidelines.
The specification section prepared by the City for TPDES Requirements should be
referred for detailed Best Management Practices for Erosion and Sediment Controls,
Stormwater Management Plans, Waste collection and disposal, off-site vehicle
tracking, and other practices.
8.2 DEFINITIONS
8.2.1 Best Management Practices (BMPs) - Schedules of activities, prohibitions of
practices, maintenance procedures, structural controls, local ordinances, and
other management practices to prevent or reduce the discharge of pollutants.
BMPs also include treatment requirements, operating procedures, and
practices to control runoff, spills or leaks, waste disposal, or drainage from
raw material storage areas.
8.2.2 Catch basins - Storm drain inlets and curb inlets to the storm drain system.
Catch basins typically include a grate or curb inlet that may accumulate
sediment, debris, and other pollutants.
8.2.3 Clean Water Act (CWA) - The Federal Water Pollution Control Act or
Federal Water Pollution Control Act Amendments of 1972, Pub.L. 92-500, as
amended Pub. . 95-217, Pub. L. 95-576, Pub. L. 96-483 and Pub. L. 97-117,
33 U.S.C. 1251 et. seq.
8.2.4 Construction Activity — means activities subject to TPDES Construction
Permits. These include construction projects resulting in land disturbance of 1
acre or more. Such activities include but are not limited to clearing and
grubbing, grading, excavating, and demolition
8.2.5 Control Measure - Any BMP or other method used to prevent or reduce the
discharge of pollutants to waters of the State.
Page 2 of 13 Stormwater Management
8.2.6 Conveyance - Curbs, gutters, man-made channels and ditches, drains, pipes,
and other constructed features designed or used for flood control or to
otherwise transport stormwater runoff.
8.2.7 Discharge - Any addition or introduction of any pollutant, storm water, or any
other substance whatsoever into the municipal separate storm sewer system
(MS4) or into waters of the United States.
8.2.8 Discharger - Any person, who causes, allows, permits, or is otherwise
responsible for, a discharge, including, without limitation, any operator of a
construction site or industrial facility.
8.2.9 Domestic Sewage - Human excrement, gray water, other wastewater from
household drains, and waterborne waste normally discharged from the sanitary
conveniences of dwellings (including apartment houses and hotels), office
buildings, factories, and institutions, that is free from industrial waste.
8.2.10 Extremely Hazardous Substance - Any substance listed in the Appendices to 40
CFR Part 355, Emergency Planning and Notification.
8.2.11 Facility - Any building, structure, installation, process, or activity from which
there is or may be a discharge of a pollutant.
8.2.12 Final Stabilization - A construction site where any of the following conditions
are met:
a. All soil disturbing activities at the site have been completed and a uniform
(for example, evenly distributed, without large bare areas) perennial
vegetative cover with a density of 70 percent of the native background
vegetative cover for the area has been established on all unpaved areas and
areas not covered by permanent structures, or equivalent permanent
stabilization measures (such as the use of riprap, gabions, or geotextiles)
have been employed.
b. For individual lots in a residential construction site by either:
i. The homebuilder completing final stabilization as specified in
condition (a) above; or
ii. The homebuilder establishing temporary stabilization for an individual
lot prior to the time of transfer of the ownership of the home to the
buyer and after informing the homeowner of the need for, and benefits
of, final stabilization.
c. For construction activities on land used for agricultural purposes (for
example pipelines across crop or range land), final stabilization may be
accomplished by returning the disturbed land to its preconstruction
Page 3 of 13 Stormwater Management
agricultural use. Areas disturbed that were not previously used for
agricultural activities, such as buffer strips immediately adjacent to a
surface water and areas which are not being returned to their
preconstruction agricultural use must meet the final stabilization
conditions of condition (a) above.
8.2.13 Garbage - Putrescible animal and vegetable waste materials from the handling,
preparation, cooking, or consumption of food, including waste materials from
markets, storage facilities, and the handling and sale of produce and other food
products.
8.2.14 Gray Water - Liquid from home clothes washing, bathing, showers, dishwashing,
or food preparation.
8.2.15 Hazardous Household Waste (HHW) - Any material generated in a household
(including single and multiple residences, hotels and motels, bunk houses, ranger
stations, crew quarters, camp grounds, picnic grounds, and day use recreational
areas) by a consumer which, except for the exclusion provided in 40 CFR §
261.4(b)(1), would be classified as a hazardous waste under 40 CFR Part 261.
8.2.16 Hazardous Waste - Any substance identified or listed as a hazardous waste by
the E.P.A. pursuant to 40 CFR Part 261.
8.2.17 Illicit Connection - Any man-made conveyance connecting an illicit discharge
directly to a municipal separate storm sewer.
8.2.18 Illicit Discharge - Any discharge to a municipal separate storm sewer that is
not entirely composed of stormwater, except discharges pursuant to this
general permit or a separate authorization and discharges resulting from
emergency firefighting activities.
8.2.19 Impaired Water - A surface water body that is identified on the latest
approved CWA §303(d) List as not meeting applicable state water quality
standards. Impaired waters include waters with approved or established total
maximum daily loads (TMDLs), and those where a TMDL has been proposed
by TCEQ but has not yet been approved or established.
8.2.20 Industrial Waste - Any liquid or solid substance that results from any process of
industry, manufacturing, mining, production, trade, or business.
8.2.21 Motor Vehicle Fluids - Any vehicle crankcase oil, antifreeze, transmission fluid,
brake fluid differential lubricant, gasoline, diesel fuel, gasoline/alcohol blend, or
any other fluid used in a motor vehicle.
8.2.22 Municipal Separate Storm Sewer System (MS4) - The system of conveyances
(including roads with drainage systems, municipal streets, catch basins, curbs,
gutters, ditches, man-made channels, or storm drains) owned and operated by the
Page 4 of 13 Stormwater Management
City and designed or used for collecting or conveying storm water, and which is
not used for collecting or conveying sewage.
8.2.23 Maximum Extent Practicable (MEP) - The technology-based discharge
standard for municipal separate storm sewer systems (MS4s) to reduce
pollutants in stormwater discharges that was established by the CWA §
402(p). A discussion of MEP as it applies to small MS4s is found in 40 CFR §
122.34.
8.2.24 Notice of Intent (NOI) - A written submission to the executive director from
an applicant requesting coverage under this general permit.
8.2.25 NPDES Permit - A permit issued by EPA (or by the State, most notably by but
not limited to the T.C.E.Q. under authority delegated pursuant to 33 USC §
1342(b)) that authorizes the discharge of pollutants to waters of the United States,
whether the permit is applicable on an individual, group, or general area -wide
basis.
8.2.26 Notice of Termination (NOT) - A written submission to the executive director
from a permittee authorized under a general permit requesting termination of
coverage under this general permit.
8.2.27 Oil - Any kind of oil in any form, including, but not limited to, petroleum, fuel
oil, crude oil or any fraction thereof which is liquid at standard conditions of
temperature and pressure, sludge, oil refuse, and oil mixed with waste.
8.2.28 Outfall - A point source at the point where a small MS4 discharges to waters
of the U.S. and does not include open conveyances connecting two municipal
separate storm sewers, or pipes, tunnels, or other conveyances that connect
segments of the same stream or other waters of the U.S. and are used to
convey waters of the U.S.
8.2.29 Person - Any individual, partnership, co -partnership, firm, company, corporation,
association, joint stock company, trust, estate, governmental entity, or any other
legal entity; or their legal representatives, agents, or assigns. This definition
includes all federal, state, and local governmental entities.
8.2.30 Petroleum Storage Tank (PST) - Anyone or combination of aboveground or
underground storage tanks that contain petroleum products and any connecting
underground pipes.
8.2.31 Point Source - Any discernible, confined, and discrete conveyance, including
but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete
fissure, container, rolling stock, concentrated animal feeding operation,
landfill leachate collection system, vessel or other floating craft from which
pollutants are or may be discharged. This term does not include return flows
from irrigated agriculture or agricultural stormwater runoff.
Page 5 of 13 Stormwater Management
8.2.32 Pollutant - Dredged spoil; solid waste; incinerator residue; sewage; garbage;
sewage sludge; munitions; chemical waste; biological materials; radioactive
materials; heat; wrecked or discarded equipment; rock; sand; cellar dirt; or
industrial, municipal, and agricultural waste discharged into water. The term
"pollutant" does not include tail water or runoff water from irrigation or rainwater
runoff from cultivated or uncultivated range land, pasture land, and farm land.
8.2.33 Rubbish — Non-putrescible solid waste, excluding ashes, that consist of (A)
combustible waste materials, including paper, rags, cartons, wood, excelsior,
furniture, rubber, plastics, yard trimmings, leaves, and similar materials; and (B)
noncombustible waste materials, including glass, crockery, tin cans, aluminum
cans, metal furniture, and similar materials that do not burn at ordinary
incinerator temperatures (1600 to 1800 degrees Fahrenheit).
8.2.34 Septic Tank Waste - Any domestic sewage from holding tanks such as vessels,
chemical toilets, campers, trailers, and septic tanks.
8.2.35 Service Station - Any retail establishment engaged in the business of selling fuel
for motor vehicles that is dispensed from stationary storage tanks.
8.2.36 Sewage (or Sanitary Sewage) - The domestic sewage and/or industrial waste
that is discharged into the City sanitary sewer system and passes through the
sanitary sewer system to the City sewage treatment plant for treatment.
8.2.37 Solid Waste - Any garbage, rubbish, refuse, sludge from a waste treatment plant,
water supply treatment plant, or air pollution control facility, and other discarded
material, including, solid, liquid, semi-solid, or contained gaseous material
resulting from industrial, municipal, commercial, mining, and agricultural
operations, and from community and institutional activities.
8.2.38 Stormwater Associated with Construction Activity - Stormwater runoff from
an area where there is either a large construction or a small construction
activity.
8.2.39 Stormwater Management Program (SWMP) - A comprehensive program to
manage the quality of discharges from the municipal separate storm sewer
system.
8.2.40 Structural Control (or Practice) - A pollution prevention practice that requires
the construction of a device, or the use of a device, to capture or prevent
pollution in stormwater runoff. Structural controls and practices may include
but are not limited to: wet ponds, bioretention, infiltration basins, stormwater
wetlands, silt fences, earthen dikes, drainage swales, vegetative lined ditches,
vegetative filter strips, sediment traps, check dams, subsurface drains, storm
drain inlet protection, rock outlet protection, reinforced soil retaining systems,
gabions, and temporary or permanent sediment basins.
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8.2.41 Used Oil (or Used Motor Oil) - Any oil that has been refined from crude oil or
synthetic oil that, as a result of use, storage, or handling, has become unsuitable
for its original purpose because of impurities or the loss of original properties but
that may be suitable for further use and is recyclable in compliance with State and
federal law.
8.2.42 Water Quality Standard - The designation of a body or segment of surface water
in the State for desirable uses and the narrative and numerical criteria deemed by
the State to be necessary to protect those uses, as specified in Chapter 307 of Title
31 of the Texas Administrative Code.
8.2.43 Waters of United States - All waters which are currently used, were used in the
past, or may be susceptible to use in interstate or foreign commerce, including all
waters which are subject to the ebb and flow of the tide; all interstate waters,
including interstate wetlands; all other waters the use, degradation, or destruction
of which would affect or could affect interstate or foreign commerce; all
impoundments of waters otherwise defined as waters of the United States under
this definition; all tributaries of waters identified in this definition; all wetlands
adjacent to waters identified in this definition; and any waters within the federal
definition of "waters of the United States" at 40 CFR § 122.2; but not including
any waste treatment systems, treatment ponds, or lagoons designed to meet the
requirements of the federal Clean Water Act.
8.2.44 Yard Waste - Leaves, grass clippings, yard and garden debris, and brush that
results from landscaping maintenance and land -clearing operations. 8.3.
8.3 ALLOWABLE STORMWATER DISCHARGES
The following non-stormwater sources may be discharged from the small MS4 and
are not required to be addressed in the small MS4's Illicit Discharge and Detection or
other minimum control measures, unless they are determined by the permittee or the
TCEQ to be significant contributors of pollutants to the small MS4, or they are
otherwise prohibited by the MS4 operator:
1. Water line flushing (excluding discharges of hyperchlorinated water, unless the
water is first dechlorinated and discharges are not expected to adversely affect
aquatic life);
2. Runoff or return flow from landscape irrigation, lawn irrigation, and other
irrigation utilizing potable water, groundwater, or surface water sources;
3. Discharges from potable water sources that do not violate Texas Surface Water
Quality Standards;
4. Diverted stream flows;
5. Rising ground waters and springs;
6. Uncontaminated ground water infiltration;
7. Uncontaminated pumped ground water;
8. Foundation and footing drains;
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9. Air conditioning condensation;
10. Water from crawl space pumps;
11. Individual residential vehicle washing;
12. Flows from wetlands and riparian habitats;
13. Dechlorinated swimming pool discharges that do not violate Texas Surface Water
Quality Standards;
14. Street wash water excluding street sweeper waste water;
15. Discharges or flows from emergency firefighting activities (firefighting activities
do not include washing of trucks, run-off water from training activities, test water
from fire suppression systems, and similar activities);
16. Non-stormwater discharges that are specifically listed in the TPDES Multi Sector
General Permit (MSGP) TXR050000 or the TPDES Construction General Permit
(CGP) TXR150000;
17. Discharges that are authorized by a TPDES or NPDES permit or that are not
required to be permitted; and
18. Other similar occasional incidental non-stormwater discharges such as spray park
water, unless the TCEQ develops permits or regulations addressing these
discharges.
8.4 STORMWATER POLLUTION PREVENTION PLAN (SW3P)
REQUIREMENTS
The U.S. Environmental Protection Agency (EPA) and the Texas Commission on
Environmental Quality (TCEQ) require that a Storm Water Pollution Prevention
Plan (SW3P) be prepared for construction activities. Construction plans shall show
proposed SW3P measures to control soil erosion and sediment pollution in storm
water discharges during construction. A notice of Intent (NOI) for Stormwater
Discharge Associated with Construction Activity under TPDES General Permit
(TXR150000) shall be completed and submitted to TCEQ. Copies of NOI, "Primary
and Secondary Operator" Notice shall be posted at the Project Site or at a prominent
place for public to viewing. The Contractor's office must keep and maintain the
updated SW3P.
The SW3P shall not be submitted for TCEQ review; however, the SW3P shall be
kept at the job site for assessment by TCEQ inspectors. The TCEQ requires that
regular weekly inspections and inspections after each storm be made of the storm
water pollution measures. A record of all inspections shall be kept. The SW3P shall
be maintained throughout the entire length (time) of the project. Should the
pollution protections not be working, the Contractor shall make adjustments in the
measures to correct the problems.
Proposed SWP3 shall contain minimum the following items:
(i) The proposed location of Refuse Area
(ii) The proposed location of Construction Exit with standard detail
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(iii) The proposed location of concrete washout Area
(iv) The proposed location of Portable Toilets
(v) The proposed location of various BMPs
(vi) The size of affected area in acreage
(vii) The location of all outfalls for stormwater discharge
(viii) locations where temporary or permanent stabilization practices are
expected to be used
(ix) locations of construction support activities, including off-site activities,
that are authorized under the permittee's NOI, including material, waste,
borrow, fill, or equipment or chemical storage areas
8.5 BEST MANAGEMENT PRACTICES
The SWP3 shall be prepared in accordance with TCEQ guidelines and should
include the implementation and maintenance of structural and non-structural best
management practices to reduce pollutants in storm water runoff from residential,
commercial, industrial and construction sites. The SW3P standard details available
for download on the City's engineering webpage can be used as guidance with the
designer's full responsibility. Below are recommended best management practices
that may include but are not limited to:
Non -Structural Practices
(i) Temporary seeding
(ii) Permanent planting, sodding, or seeding
(iii) Mulching
(iv) Soil Retention Blanket
(v) Buffer Zone
(vi) Preservation of Natural Resources
Structural Practices
(i) Reinforced Silt Fence/ silt fence
(ii) Hay Bales
(iii) Rock Filter Dams
(iv) Pipe Slope Drains
(v) Paved Flumes
(vi) Channel Liners
(vii) Sediment Basins/ Detention Basin
(viii) Rock bedding at Construction exit
(ix) Curb and Gutters
(x) Velocity control devices
(xi) Erosion Control logs
All protective measures identified in the SWP3 must be maintained in effective
operating condition. If, through inspections or other means, the construction site
operator determines that BMPs are not operating effectively, then the
construction site operator shall perform maintenance as necessary to maintain the
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continued effectiveness of storm water controls, and prior to the next rain event if
feasible. Erosion and sediment controls that have been intentionally disabled,
run -over, removed, or otherwise rendered ineffective must be replaced or
corrected immediately upon discovery. If periodic inspections or other
information indicates a control has been used incorrectly, is performing
inadequately, or is damaged, then the operator must replace or modify the control
as soon as practicable after making the discovery. If sediment escapes the site,
accumulations must be removed at a frequency that minimizes off-site impacts,
and prior to the next rain event, if feasible. If the construction site operator does
not own or operate the off- site conveyance, then the permittee must to work with
the owner or operator of the property to remove the sediment.
a. Rock Filter Dam Maintenance - The rock filter dam shall be inspected every
two weeks or after each 1/2" rain event and shall be replaced when the
structure ceases to function as intended due to silt accumulation among the
rocks, washout, construction traffic damage, etc. When silt reaches a depth
equal to one-third of the height of the berm or one foot, whichever is less;
the silt shall be removed and disposed of properly. When the site is
completely stabilized, the berm and accumulated silt shall be removed and
disposed of in an approved manner.
b. Stabilized Construction Exit Maintenance - When sediment has substantially
clogged the void area between the rocks, the aggregate mat must be washed
down or replaced. Periodic re -grading and top dressing with additional stone
must be done to keep the efficiency of the entrance from diminishing. See
COP specification for Stabilized Construction Exit for details.
c. Curb Inlet Protection Maintenance - Inspection shall be made by the
contractor and silt accumulation must be removed when depth reaches 2".
Contractor shall monitor the performance of inlet protection during each
rainfall event and immediately remove the inlet protections if the stormwater
beings to overtop the curb. Inlet protection shall be removed as soon as the
site has reached final stabilized.
d. Silt Fence Maintenance - Inspection shall be made after each 1/2" rainfall,
daily during period of prolonged rainfall, and at a minimum once each
week. Repair or replacement shall be made promptly as needed. Silt fence
shall be removed when the site is completely stabilized so as not to block or
impede storm flow or drainage. Accumulated sediment shall be removed
when it reaches a depth of one-third the height of the fence or 6 inches,
whichever is less. The silt shall be disposed of at an approved site and in
such a manner' as to not contribute to additional siltation.
e. Erosion Control Blanket Maintenance - Erosion control blankets should be
inspected regularly for bare spots caused by weather or other events.
Missing or loosened blankets must be replaced or re -anchored. Check for
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excess sediment deposited from runoff. Remove sediment and/or replace
blanket as necessary. In addition, determine the source of excess sediment
and implement appropriate measures to control the erosion. Also check for
rill erosion developing under the blankets. If found, repair the eroded area.
Determine the source of water causing the erosion and add controls to
prevent its reoccurrence.
f. Dewatering Controls Maintenance - Dewatering controls should be inspected
regularly. Dewatering discharge points should be checked for erosion. Eroded
areas should be repaired, and erosion controls should be installed to prevent
future erosion. Dewatering pumps and sediment controls should be
monitored, at least hourly, while pumps are in operation to prevent
unauthorized discharge and to catch erosion problems or control failure.
Conventional sediment controls should be inspected at least weekly when
used for continuous dewatering, because they will become overcome with
sediment more quickly than when used to control runoff from storm events.
The controls shall be maintained according to the criteria in their respective
sections.
g.
They should be replaced when they no longer provide the necessary level of
sediment removal. Sediment filter bags should be checked to determine if
they need replacing. The bags cannot be cleaned or reused. They should be
used until they reach the manufacturer's recommended capacity. The entire
bag with sediment can be disposed of as solid waste. If a controlled location
onsite or a spoil site is available, the bag can be cut open and the sediment
spread on the ground. Only the bag is waste in this case.
Concrete Washout Maintenance - Concrete waste management controls
should be inspected regularly for proper handling of concrete waste. Check
concrete washout pits and make repairs as needed. Washout pits should not be
allowed to overflow. Maintain a schedule to regularly remove concrete waste
and prevent over -filling. If illicit dumping of concrete is found, remove the
waste and reinforce proper disposal methods through education of employees.
Per TCEQ requirements, erosion control and stabilization measures must be
initiated as soon as practicable in portions of the site where construction
activities have temporarily ceased. Stabilization measures that provide a
protective cover must be initiated as soon as practicable in portions of the site
where construction activities have permanently ceased. Except as provided in (A)
through (C) below, these measures must be initiated no more than 14 days after
the construction activity in that portion of the site has temporarily or permanently
ceased:
A. Where the initiation of stabilization measures by the 14th day after
construction activity temporarily or permanently ceased is precluded by
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snow cover or frozen ground conditions, stabilization measures must be
initiated as soon as practicable
B. Where construction activity on a portion of the site has temporarily
ceased, and earth disturbing activities will be resumed within 21 days,
temporary erosion control and stabilization measures are not required on
that portion of site.
C. In areas where temporary stabilization measures are infeasible, the operator
may alternatively utilize temporary perimeter controls. The operator must
document in the SWP3 the reason why stabilization measures are not
feasible, and must demonstrate that the perimeter controls will retain
sediment on site to the extent practicable.
8.6 POST CONSTRUCTION STORMWATER MANAGEMENT IN NEW
DEVELOPMENT AND REDEVELOPMENT
Post -construction storm water management in new and redevelopments should
include minimum control measures to control post -construction runoff. The
minimum control measures below are acceptable and others may be considered on
the case-by-case basis. Minimum Control Measures:
a) Alternative Turnarounds - Dead end streets in residential subdivisions are
usually required to have an acceptable option for vehicles to turnaround, with the
circular cul-de-sac being the most common. The amount of impervious cover can
be reduced from the standard impervious cul-de-sac. It is acceptable to place a
landscaped island in the center of the cul-de-sac turnaround as long as it maintains
an acceptable turning radius. Alternative turnarounds can be applied in the design
of residential, commercial, and mixed-use development. They may be combined
with alternative pavers, biorentention areas, and other techniques in an effort to
reduce the runoff from the site.
b) Grassed Swales - A grass swale is a stable turf, parabolic or trapezoidal
channel used for water quality or to convey stormwater runoff, which does not
rely on the permeability of the soil as a pollutant removal mechanism. Grass
swales are used to reduce particulate pollutants due to settling and filtration.
Particulate pollutant removal occurs when the low velocities and shallow depths
allow particulate settling and the grass blades act to filter runoff from the water
quality design storm. Grass swales are best suited to transport and treat
stormwater runoff generated from impervious surfaces with small drainage
areas. Grass swales can be used wherever soil conditions and slopes permit the
establishment and maintenance of a dense stand of vegetative cover. Typically,
swales have a minimum bottom width of 2 feet to 10 feet and have a recommended
side slope of 4:1.
c) Catch Basin Insert - Catch basins, also known as storm drain inlets and curb
inlets, are inlets to the storm drain system. Inserts can be designed to improve
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water quality by removing oil and grease, trash, debris, and sediment can improve
the efficiency of catch basins. Some inserts are designed to drop directly into
existing catch basins, while others may require retrofit construction.
d) Wet Ponds - Wet ponds (a.k.a. stormwater ponds, wet retention ponds, wet
extended detention ponds) are constructed basins that have a permanent pool of
water throughout the year (or at least throughout the wet season). Ponds treat
incoming stormwater runoff by allowing particles to settle and algae to take up
nutrients. The primary removal mechanism is settling as stormwater runoff
resides in this pool, and pollutant uptake, particularly of nutrients, also occurs
through biological activity in the pond. Wet ponds are generally on-line, end -of -
pipe BMPs. The primary pollutant removal mechanism in a water pond is
sedimentation. Significant loads of suspended pollutants, such as metals,
nutrients, sediments, and organics, can be removed by sedimentation. Wet ponds
can be used at residential, commercial and industrial sites. Wet ponds may be
single -purpose facilities, providing only runoff treatment, or they may be
incorporated into an extended storage or a detention pond design to also provide
flow control.
8.7 STORMWATER AND ILLICIT DISCHARGE ORDINANCE
The City of Pearland Illicit Discharge Ordinance shall be referred for the details of
allowable discharge, prohibited discharge, and penalty for violation of the
ordinance.
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