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Ord. 0908 06-28-99 TabledTabled 06/28/99 ORDINANCE NO. 908 AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF PEARLAND, TEXAS, ADOPTING A MASTER DRAINAGE PLAN FOR TAX INCREMENT REINVESTMENT ZONE NO. 2 ("TIRZ#2); HAVING A SAVINGS CLAUSE, A SEVERABILITY CLAUSE, AND A REPEALER CLAUSE. WHEREAS, the City Council, at its December 14, 1998, meeting, created City of Pearland TIRZ#2; and WHEREAS, the interlocal participation agreement with Brazoria Drainage District No. 4 ("District") requires both the City and the District to approve a Master Drainage Plan for TIRZ#2; and WHEREAS, the City and the District met on April 2, 1999, and agreed upon the standards under which the Master Drainage Plan should be developed; now, therefore, BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF PEARLAND, TEXAS: Section 1. That the City Council, subject to concurrence by both the City and District Engineers, hereby adopts the Master Drainage Plan, a copy of which is attached hereto as Exhibit "A" and made a part hereof for all purposes, to guide and direct the design of drainage development and improvements in the City of Pearland, Texas. Section 2. Savings. All rights and remedies which have accrued in favor of the City under this Ordinance and amendments thereto shall be and are preserved for the benefit of the City. Section 3. Severability. If any section, subsection, sentence, clause, phrase or portion of this Ordinance is for any reason held invalid, unconstitutional or otherwise unenforceable by any court of competent jurisdiction, such portion shall be deemed a 1 ORDINANCE NO. 908 separate, distinct, and independent provision and such holding shall not affect the validity of the remaining portions thereof. Section 4. Repealer. All ordinances and parts of ordinances in conflict herewith are hereby repealed but only to the extent of such conflict. PASSED and APPROVED ON FIRST READING this the —1{ day of T A. D., 1999. TOM EID MAYOR ATTEST: YOUNG LORFING CITY SECRETARY PASSED and APPROVED ON SECOND AND FINAL READING this the day of , A. D., 1999. ATTEST: YOUNG LORFING CITY SECRETARY TOM REID MAYOR 2 ORDINANCE NO. 908 APPROVED AS TO FORM: DARRIN M. COKER CITY ATTORNEY 3 t 1 1 1 i i i 1 MASTER DRAINAGE PLAN SHADOW CREEK RANCH PLANNED UNIT DEVELOPMENT FOR SHADOW CREEK RANCH DEVELOPMENT COMPANY CITY OF PEARLAND, BRAZORIA COUNTY, TEXAS BRAZORIA DRAINAGE DISTRICT NO. 4 FORT BEND COUNTY DRAINAGE DISTRICT HARRIS COUNTY FLOOD CONTROL DISTRICT CAROLYN SUE GILLIGAN June 1999 LJA Engineering & Surveying, Inc. 2929 Briarpark, Suite 500 Houston. Texas 77042-3703 Phone 713.953.5200 Fax 713.953.5026 LJA Job Number 1545-9805 Shadow Creek Ranch Master Drainage Plan EXECUTIVE SUMMARY Shadow Creek Ranch is a 3350-acre planned development located west of State Highway 288, approximately 23 miles south of downtown Houston, Texas. Bounded on the north by Clear Creek, on the south by Country Road 92 (future FM 518) and on the west by Farm to Market Road 521 (FM521), the entire site is within the City of Pearland, Texas city limits. Approximately 46 acres are in Harris County; approximately 630 acres are in Fort Bend County with the remaining acreage in Brazoria County. Harris County Flood Control District, Fort Bend County Drainage District and Brazoria Drainage District No. 4 all have jurisdiction over flood control and drainage in their respective counties. The analysis for this Master Drainage Plan uses the recently adopted Storm Drainage Design Criteria (DDC) for the City of Pearland to determine rainfall runoff. Approximately one-third of the total Shadow Creek Ranch area is within the effective Clear Creek floodplain. Additionally, approximately 240 acres is also within the Clear Creek floodway. The base flood elevations range from approximately 57 feet at the eastern boundary to approximately 63 feet at FM 521. To eliminate the floodplain in areas to be developed, land below these base flood elevations will be filled. Excess rainfall runoff from the development will be detained in over 23 proposed lakes scattered throughout the 3350 acres. Analysis determining the required storage volume used the following design assumptions: • The site filled to at least one foot above the effective base flood elevation. • Existing effective 100-year base flood elevation is considered the maximum ponding elevation. Since the floodplain varies across the site, the maximum ponding elevations also vary. • Normal pool elevations are limited by the flowline of Clear Creek. • Lake side slopes are minimum 6H:1 V; therefore, no separate maintenance berm is required. (Note: the lakes and channels will be maintained by a special maintenance district) The total volume of storage needed for Shadow Creek Ranch is approximately 2800 acre-feet. Over 2000 acres of land south of County Road 92 currently drains through Shadow Creek Ranch via channels that are part of the Brazoria Drainage District No. 4 system. Existing flow entering the Shadow Creek Ranch site is controlled by existing structures under CR 92. Although most of this offsite runoff will flow through the development without attenuation, some detention of these flows will occur. By detaining some of the offsite runoff, the total flow in Clear Creek upstream of State Highway 288 will be reduced. The total area reserved for lakes and detention areas is approximately 322 acres. Approximately 140 acres will be dedicated for internal channels. In addition to the reduced flow in Clear Creek, approximately 1900 acres of land that now drains to the Country Place Ditch will be re-routed through Shadow Creek Ranch. This diversion will improve ES-1 Shadow Creek Ranch Master Drainage Plan existing drainage conditions in the Country Place Ditch by reducing the upstream drainage area. The modelled flow rates are reduced by almost 50 percent. The Brazoria Drainage District No. 4 Flood Protection Plan recommends about 12,000 acre-feet of regional detention to alleviate flooding along Clear Creek within the District boundaries. Detention storage planned for Shadow Creek Ranch would provide about 25 percent of the recommended detention volume and begin implementation of this regional detention plan. Hydrologic analysis followed the methods described in Section 6 of the DDC. This method uses the U.S. Army Corps of Engineers HEC-1 "Flood Hydrography Package" computer model to simulate the precipitation -runoff process and compute flood hydrographs at desired locations within a watershed. The point rainfall amounts, rainfall distributions, loss rates and regionalized equations used in the HEC-1 models were obtained from the referenced text. An existing conditions model of the Clear Creek watershed was prepared to determine the existing flows affecting Clear Creek. For the existing conditions model, all of the subwatersheds proposed for Shadow Creek Ranch were modeled in their undeveloped condition. This model was then revised to reflect Shadow Creek Ranch in its developed conditions. In this way an accurate comparison of the impacts of the development could be made. The hydrographs generated by the developed conditions HEC-1 model were entered into the adICPR hydraulic model of the proposed Shadow Creek Ranch drainage system. After routing through the proposed lakes and channels, the outflow hydrographs were then re-entered into the overall Clear Creek HEC-1 model. The results of the modeling indicate that 100-year flows entering Clear Creek are reduced by approximately 275 cfs to 1900 cfs, depending on the location along the channel. ES-2 Shadow Creek Ranch Master Drainage Plan 1.0 INTRODUCTION 1.1 Purpose and Objective For development to occur orderly and economically, proper planning is essential. A master drainage plan for the overall development provides the planning vehicle for drainage infrastructure. This report presents an overall plan for drainage within Shadow Creek Ranch, including channel and right-of-way dimensions, detention analysis of the proposed lakes and analysis of the proposed Clear Creek floodplain and floodway modifications. This information is presented in enough detail to give developers the information needed to proceed with land planning, but has flexibility to change as development plans are modified. This report is intended for inclusion in the review process for planning and platting, however, due to the size of Shadow Creek Ranch, this overall plan is being submitted well before platting. The following sections present the overall approach to moving rainfall runoff from Shadow Creek Ranch to Clear Creek. The rainfall distribution, loss rates and hydrograph parameters comply with Section 6 of the DDC. Computer models of the proposed detention system, including approximate volume and proposed control structures are explained and the results presented. It is understood that the development of over 3300 acres of land will occur over a long period of time. During this time, specific details the the drainage plan may change. This initial submittal presents and overview of the drainage concepts as they are currently planned. Additional, and more detailed analysis, especially concerning the proposed fill in the Clear Creek floodplain, and the proposed revisions to the Clear Creek floodway, will be submitted in subsequent reports. 1.2 Site Location and Description Shadow Creek Ranch is approximately 23 miles south of downtown Houston, Texas, as shown on Exhibit 1.1, Vicinity Map. Bounded on the north by Clear Creek, on the south by County Road 92 (future FM 518), on the east by State Highway 288 (SH 288) and on the west by Farm to Market Road 521 (FM 521), the entire 3350 acres planned for the development is within the City of Pearland, Texas city limits. The site is where the boundaries of Harris, Fort Bend and Brazoria Counties converge. Most of the site is in Brazoria County. Approximately 46 acres in the northwest corner are in Harris County; the western 630 acres along FM 521 are in Fort Bend County. As part of the Gulf Coast plain, the site is characterized by extremely flat topography. Soils in the area are mostly Lake Charles clay or Bernard clay loam. These soils are characterized by low permeability but slow surface runoff potential. Annual rainfall averages 45 inches, with periods of intense rainfall associated with tropical storms and localized thunderstorms occurring frequently throughout the year. Page 1-1 Shadow Creek Ranch Master Drainage Plan Several Clear Creek tributary channels that are part of the Brazoria Drainage District No. 4 (BDD4 or District) drainage system currently•traverse the Shadow Creek Ranch site. These channels include A-124-00-00, A 127-00-00 and A-128-00-00 and their tributaries as shown on the Brazoria Drainage District No. 4 General Drainage Map. According to the Flood Insurance Rate Maps (FIRM's) for Harris, Fort Bend and Brazoria Counties, approximately one-third of the total Shadow Creek Ranch area is within the effective Clear Creek floodplain. Another approximately 240 acres is within the Clear Creek floodway. Exhibit 1.2 shows the limits of the Clear Creek floodplain and floodway on the Shadow Creek Ranch site. Effective base flood elevations (BFE's) range from approximately 57 feet at the eastern boundary of Shadow Creek Ranch to approximately 63 feet at FM 521. During the development process, land areas below the BFE's will be filled to elevate the land above the floodplain. The existing floodplain storage will be mitigated to allow redefinition of the floodplain and floodway. As part of the initial planning and design, a Conditional Letter of Map Revision (CLOMR) request will be prepared and submitted to the Federal Emergency Management Agency (FEMA). The CLOMR will provide technical data explaining how the floodplain and floodway will be reduced. This will allow FEMA to concur that "if the project is constructed as presented, a change to the flood plain and floodway will be warranted". When construction has been completed, a request will be made to FEMA for a Letter of Map Revision (LOMR). The LOMR request will include as -built data and provide FEMA with the technical information necessary to remove the floodplain from within Shadow Creek Ranch. 1.3 Existing Flood Protection Plan In November 1997, BDD4 published a Flood Protection Plan for the five watersheds that provide the primary drainage system for the District: Clear Creek, Hickory Slough, Mary's Creek, Cowart Creek and Chigger Creek. The Plan includes the following parts: • • • analysis of the existing primary drainage systems with verification of the computer models to actual storm events the impact of future development on the existing drainage system recommendations of methods for reducing flooding within the BDD4 jurisdiction. These recommendations were incorporated in the design of the Shadow Creek Ranch drainage facilities to ensure that the design would compliment the Plan. Specific plan elements that will be implemented with the Shadow Creek Ranch development are discussed in subsequent sections of this report. During the preparation of the Flood Protection Plan flooding complaints from local residents were compiled. The locations of the flooding complaints are included in the report, as were problem areas identified by BDD4 staff and locations of homes that filed flood insurance claims to FEMA in the previous five years. A review of this exhibit shows only one "citizen flooding complaint" is located in the area affected by the proposed Shadow Creek Ranch development. This complaint is Page 1-2 ■ ■ ■ Shadow Creek Ranch Master Drainage Plan downstream of SH 288 along Clear Creek tributary A-124-00-00. When the drainage plan for Shadow Creek Ranch is complete, approximately 842 acres within Shadow Creek Ranch and 1900 acres of the A-124-00-00 drainage area upstream of SH 288 will be diverted directly to Clear Creek. This diversion will reduce the total area of the watershed by two-thirds and reduce runoff affecting the complaint area. Results of the Flood Protection Plan confirmed that Clear Creek has significant flooding along its length within the planning area. Most of the flooding is due to insufficient channel capacity and high backwater conditions. Only two alternatives investigated for the Flood Protection Plan can be designed and constructed without increasing downstream flooding or adversely affecting existing neighborhoods within BDD4. The two alternatives are channel clean out and upstream regional detention. While neither alternative provides 100-year protection along Clear Creek, flooding problems would reduced at several specific sites. Upstream regional detention that would detain 100-year flows to approximately the 10-year frequency level was evaluated. The Flood Protection Plan concludes that approximately 12,000 acre feet with a surface area of 1,000 acres and a depth of 14 feet is required. However, it is also noted that multiple facilities can serve the same function and allow for phasing of detention. The detention project was the largest and most costly project evaluated in the Flood Protection Plan ($54.3 Million for land and construction). In the recommended plan for Clear Creek from the Flood Protection Plan, the only structural • improvements recommended for Clear Creek is regional detention. According to the 5- and 10- year Implementation Plans, this regional detention alternative will not be implemented in either plan. With the development of Shadow Creek Ranch the detention required for approximately 3350 acres will be constructed, thus initiating implementation of that portion of the Flood Protection Plan. 1.4 Drainage Design Criteria As indicated previously, Shadow Creek Ranch lies in portions of three counties and within the City of Pearland. Accordingly, the drainage design proposed for the development should satisfy the rules, regulations and guidelines of several drainage agencies. Harris County Flood Control District (HCFCD), Fort Bend County Drainage District (FBCDD), Brazoria Drainage District No. 4 (BDD4) and the City of Pearland all have published criteria for drainage design. The rainfall runoff values from the City of Pearland criteria were used for this Master Drainage Plan for Shadow Creek Ranch. 1.5 Preliminary Design Assumptions BDD4 rules require contours for surveys of land in a flood hazard area to be based on the National Geodetic Vertical Datum (NGVD 29), 1987 datum adjustment. Since topography of Shadow Creek Ranch based on 1987 adjustment was not immediately available, the maximum allowable ponding elevation in the various lakes being modeled was limited to the effective base flood elevation (BFE) Page 1-3 Shadow Creek Ranch Master Drainage Plan as shown on the Brazoria County, Harris County and Fort Bend County Flood Insurance Rate Maps (Firm's). For each lake, it was assumed that the natural ground would be filled to one foot above the BFE. Using these assumptions, major adjustments to the lake volumes would not be required once the 1987 adjusted topography became available. Therefore, the following information was used in developing the hydrologic and hydraulic models of Shadow Creek Ranch. • Effective FEMA Clear Creek HEC-2 model A1000FW.FEM obtained from Harris County Flood Control District, based on NGVD 29, 1973 adjustment. • Clear Creek HEC-1 model A100 RLJ.100 prepared for the BDD4 Flood Protection Plan. • The Brazoria Drainage District No. 4 General Drainage Map with one foot contour intervals adjusted to 1978 datum. • Brazoria County FIRM Panel 48039C0010 H, Effective Date: June 5. 1989. • Harris County FIRM Panel 48201 C 1010 J, Effective Date: November 6, 1996. After aerial photography was obtained, these assumptions were reviewed and it was determined that major adjustments to computer models used for the analysis were not warranted. Aerial topography of Shadow Creek Ranch was received in late December 1998. The aerial topography is based on North American Vertical Datum (NAVD 88), 1991 adjustment. According to the National Geodetic Survey, the vertical elevation difference between NVGD 29, 1987 adjustment and NAVD 88, 1991 adjustment is .02 feet. Therefore,considering the limitations of the hydrologic and hydraulic computer programs used for analysis, the aerial topography is essentially the same elevation as required by BDD4 Rules. Page 1-4 Shadow Creek Ranch Master Drainage Plan 4.0 RESULTS AND CONCLUSIONS Approximately 3000 acre-feet of detention storage will be provided by the Shadow Creek Ranch lakes, reducing both the 100- and 10-year peak flows entering Clear Creek between FM 521 and the confluence with A-124-00-00 (Country Place Ditch). The amount of flow reduction depends on the location of the proposed Shadow Creek Ranch outfalls along Clear Creek. Based on the preliminary land plan, three outfalls and one diversion into the development will be constructed. The diversion will be just downstream of FM 521. Outfalls will be located at the current A-128-00-00 and A127- 00-00 outfall locations, and just upstream of SH 288. Conveying rainfall runoff from approximately 3200 off -site acres through the Shadow Creek Ranch lakes will also reduce the existing peak flows in Clear Creek. Additionally, the peak flow in A-124- 00-00 (Country Place Ditch) will be reduced, alleviating some of the existing flooding problems along the channel. At the confluence of Clear Creek and A-124-00-00 (Country Place Ditch), the 100-year peak flow will be reduced by approximately 1600 cfs Upstream of SH 288, the peak 100-year flow will be reduced by approximately 700 cfs. Diverting a portion of the Clear Creek flow through the Shadow Creek Ranch system will reduce the 100-year peak flow at Almeda School Road by approximately 1600 cfs. Reducing the flows will lower the base flood elevations along this reach of Clear Creek, which will also allow a re -definition of the floodway, reclaiming additional land for development. The next step in reclaiming this land is preparation of a request for a CLOMR for submittal to FEMA. Page 4-1 C. CONSIDERATION AND POSSIBLE ACTION - SECOND AND FINAL READING OF ORDINANCE NO. 908 - AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF PEARLAND, TEXAS, ADOPTING A MASTER DRAINAGE PLAN FOR TAX INCREMENT REINVESTMENTZONE NO. 2 ("TIRZ"#2); HAVING A SAVINGS CLAUSE, A SEVERABILITY CLAUSE, AND A REPEALER CLAUSE. Councilmember Seeger made the motion, seconded by Councilmember Beckman, to approve Ordinance No. 908 on its second and final reading. Mayor Pro-Tem Berger stated that it is his understanding that the Drainage Commission or their Engineer has reviewedthe plan and he does not know if our engineer has reviewed it. He stated that he would like to see the comments from the County's perspective and the City's before further action is taken, therefore, he will be tabling Ordinance No. 908. Mayor Pro-Tem Berger made the motion, seconded by Councilmember Seeger, to table Ordinance No. 908 on its second and final reading. Voting "Aye" Councilmembers Berger and Seeger. Voting "No" Councilmember Beckman. Motion Passed 2 to 1, with Councilmembers Tetens and Wilkins absent. NEW BUSINESS: COUNCIL ACTION - RESOLUTION NO. R99-53 - A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF PEARLAND, TEXAS, AUTHORIZING THE CITY MANAGER OR HIS DESIGNEE TO APPLY FOR AND EXECUTE ALL AGREEMENTS RELATED TO THE 1999 TEXAS PARKS AND WILDLIFE DEPARTMENTS RECREATIONAL TRAILS PROGRAM AND ALLOCATING MATCHING FUNDS FROM THE CITY OF PEARLAND. Councilmember Beckman made the motion, seconded by Mayor Pro-Tem Berger, to approve Resolution No. R99-53. Parks and Recreation Director, Ed Hersh, stated that this is a continuation of Mary's Creek and Independence Park walking trail. It will be extended one quarter of a mile, east from Pasternak Park. Mr. Hersh stated that he has discussed this project with Mike Yost Page 5 of 13 - 6/28/1999 Memo To: Mayor and Council Members From: Alan Mueller Date: June 10, 1999 Subject: Shadow Creek Ranch Master Drainage Plan Background The interlocal participation agreement with BDD4 calls for the City and BDD4 to both approve a Master Drainage Plan for Shadow Creek Ranch before any plats are approved within the development. The basis for this clause in the agreement is BDD4's concerns that the development not' cause problems downstream on Clear Creek. Since the development is within Pearland's city limits, BDD4 can not enforce its own drainage/detention rules. However, to gain a more widespread assurance that the development will not cause downstream problems and to gain BDD4's TIRZ participation, the agreement calls for the plan to be developed under a mutually agreeable design standard. Engineers and staff from the City, BDD4, and developer met on April 2, 1999, and agreed upon the standards under which the plan should be developed. LJA Engineering developed the plan in accordance with these standards and submitted to the City and BDD4 engineers for review in early June 1999. Attachments Attached are the Executive Summary, Introduction, and Conclusion sections of the Plan. The Plan has been reviewed by John Hargrove, City Engineer, Andy Gallagher, Assistant City Engineer and Flood Plain Administrator for the City. Andy stated that he has a few minor remaining questions regarding the Plan, but that the intent of the Plan has been met and the concept is agreed to. Recommendation At this point, staff recommends approval of the Plan subject to final concurrence by both the City Engineer and Drainage District Engineer.