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Shadow Woods-CS 891006The City With A Beautiful Future October 6, 1989 FILr. COPY P.O. Box 478 Coppell, Texas 75019 214-462-0022 Mr. Frank Pagano FEMA, Region VI, Federal Center 800 North Loop 288 Denton, Texas 76201-3698 SUBJECT: Shadow Woods Estates/Floodplain Reclamation Coppell, Texas Dear Mr. Pagano: The City of Coppell has received the enclosed technical report on existing and proposed floodplain reclamation studies regarding above project. Shadow Woods Estates is located on the southeast corner of Sandy Lake and Coppell Road, along Cottonwood Branch. Please note that this project has been review by Mr. Ron Morrison with Kimley-Horn & Associates, Inc. on behalf of the City of Coppell. As stated in his attached letter dated July 2, 1989, "... the modeling effort is correct..". The two items of concern, as listed, have been addressed and this project is in compliance with Coppell's Floodplain Ordinance #87390. We are forwarding two sets of technical reports on this project for information purposes only, since it does not require a map change. If you have any questions, please contact Shohre Daneshmand or myself at (214) 462-8495. RRD/SD/bb xc: Steve Goram, Director of Public Works Ron Morrison, Kimley-Horn & Associates, Inc. Michael Boyd, Nathan D. Maier - Kimley-Horn and Associates, Inc. 12660Coit Road, Suite 200, Dallas, Texas 75251 · (214) 386-7007 Raleigh, Charlotte, Nashvitle, Virginia Beach, Washington, Dallas, Phoenix, Mr. Russel D/gyle, P.E. City Engine/gr City of ~5ppell P. O. J)fx 478 CoppeR1, Texas 75019 West Palm Beach, Tampa, Orlando, Ft. Lauderdale, Veto Beach, Ft. Myers, Stuart Re: Review of Shadowwoods Estates Floodplain Reclamation by Nathan D. Maier Consulting Engineers for Compliance with the City Floodplain Ordinance Dear Mr. Doyle: We have completed the review of the subject study for compliance with the city floodplain ordinance. Th'e subject study identified an existing condition floodplain that was significantly higher than the floodplain currently being used as a baseline by the city. This is because of better field survey data which identified a high ground not previously modeled. Our review of the material presented indicates that the modeling effort is correct. However there are two minor items that must be included before the study complies with the city floodplain ordinance. They are as follows: 1. According to Article 5c-6 the lowest floor elevation for each lot must be shown on the site grading plan. This was not completed. 2. According to Article 5c-5 the boundary of the floodplain and floodway must be shown on the plat. Only the floodway was shown on the plat, the floodplain needs to be shown as well. We suggest that this submittal be forwarded to FEMA for information purposes only, since it does not require a map change and does not increase the existing FIS floodplain. Building client relationships since 1967 Shadowwoods Estates July 2, 1989 Pa~e -Two- Sincerely, KIMLEY-HORN AND ASSOCIATES, INC. · Morrison, P.E. Senior I'lydrologist If we can provide further information please call me. We also request that a copy of the study be provided on a DSDD Floppy Disk so that we can update the current city floodplain study throuah the area. I Cottonwood Creek CITY OF COPPELL, TEXAS FLOODPLAIN DETERMINATION AND RECLAMATION FOR SHADOW WOODS ESTATES Southwest of Sandy Lake Road West of Coppell Road June 9, 1989 CONSULTING ENGINEERS. INC, Dallai, Texa. (214) 739-4741 NATHAN D. MAIER CONSULTING ENGINEERS, INC. June 9,1989 Mr. Russell R. Doyle, P.E. City Engineer City of Coppell P.O. Box 478 Coppell, Texas 75019 Re: Cottonwood Creek, Coppell, Texas Shadow Woods Estates NDM No.: 88-10-116 Dear Mr. Doyle: Attached is a hydraulics study for Cottonwood Creek between Sandy Lake Road and State Road. Addi- tional field surveyed cross sections have been added to the City floodplain study within this reach of Cottonwood Creek to facilitate a detailed delineation of the required floodplain criteria. Included within this study is documentation and engineering data to support the Shadow Woods Estates development. A' description of the project and a summary of Items required by the City of Coppell Floodplain ordinance 87390 are provided. We are requesting that you review this data and, if acceptable, grant us authorization to proceed with the final subdivision engineering plans. If you need further information, please give me a call. Sincerely, NATHAN D. MAIER CONSULTING ENGINEERS, INC. Michael H. Boyd Project Engineer MHB/rdp Attachment orthPark/8800 N. Central Expwy./Suite 300/Dallas, Texas 75231 (21,4) 739-474! 1,0 2.0 3.0 4.0 5.0 6.0 7.0 OTTONWOOD CREEK CITY OF COPPELL, TEXAS Shadow Woods Estates TABLE OF CONTENTS INTRODUCTION METHODOLOGY WATER SURFACE PROFILES, 100-YEAR HEC-2 HYDRAULIC MODELS CONCLUSIONS EXHIBIT 1 -- Vicinity Map EXHIBIT 2 -- Location Map EXHIBIT 3 -- Floodplain/Cross Section Map EXHIBIT 4 -- Water Surface Profile Plot EXHIBIT 5 -- Stream Cross Section Plots EXHIBIT 6 -- Detailed Topo and Reclamation Plan EXHIBIT 7 -- Subdivision Plat EXHIBIT 8 -- Subdivision D.A. Map HEC-2 COMPUTER RUNS 7.1 7.2 7.3 7.4 7.5 Current City Existing Extended Existing Proposed Reclamation FIS Floodway Extended FIS Floodway COTTONWOOD CREEK Shadow Woods Estates Coppeii, Texas 1.0 INTRODUCTION Shadow Woods Estates is a proposed 22-acre residential development located southwest of Sandy Lake road and CoPpell Road. The easterly property limit is within the channel of Cottonwood Creek. See Exhibit 2, Location Map. · This report delineates the floodplain for the two-year ultimate, 100-year existing (FEMA), and 100-year ultimate. Reclamation is proposed outside of the 100-year existing (FEMA), but within the 100-year ultimate. To define the floodplain, additional field surveyed cross sections were added to the current City HEC-2 computer model. This report also expands the current effective FIS floodway determination with additional cross sections located along the reach of Cottonwood Creek within the proposed development. The resultant water surfaces are mapped on a 1-foot interval topography map (see Exhibit 6). Low flow (less than 10 cfs) is contained within the main channel of Cottonwood Creek. This Iow flow was determined from records published by the U.S. Geological Survey (USGS). 2.0 METHODOLOGY The hydraulic parameters for this project are the same as the current City of Coppell Cottonwood Creek floodplain study. The existing HEC-2 data were obtained from Kimley-Hom & Associates, lnc. This engineering firm prepared the existing Cottonwood Creek study. The discharges, starting water surface elevations, cross section data, "n" values, and expansion and contraction coefficients were included in this data. Computer run 7.1 is a duplication of the data provided. A second existing conditions HEC-2 computer analysis that includes new stream cross sections was run · for the two-year ultimate, 100-year existing, and 100-year ultimate floodplains. New cross sections added between Sandy Lake Road and State Road are 10120, 10210, 10470, 10655, 10830, 11030, 11380, 11880, and 12420. These cross section locations are shown on exhibits 3 and 6. See computer run 7.2 for the input, detailed output, and summary tables. The projected subdivision improvements are modeled in a third HEC-2 computer analysis. This run revises the existing condition model by showing floodplain reclamation of the ultimate 100-year flood- plain. No reclamation is proposed within the two-year ultimate or the 100-year existing floodplain. See Exhibit 5, cross section plots, and Exhibit 6 for the proposed reclamation limits. See computer run 7.3 for the applicable input and output. , Foudh and fifth HEC-2 computer runs (7.4 and 7.5) are duplications of the current effective FIS floodway run, and an expanded floodway run that includes the new cross sections, respectively. See Exhibit 3 for a delineation of the floodway and base flood elevations. 3.0 WATER SURFACE PROFILES, 100-YEAR The methodology and starting parameters for the revised profiles are the same as used in the effective City study. Upstream of the project area, the 100-year base flood elevations and floodway location coin- cide with the effective FIS profiles. This study added cross section numbers 10120, 10210, 10470, 10655, 10830, 11030, 11380, 11880, and 124'20 to the City data. These cross section data were taken from recent field surveys. Following is a resultant table of water surface elevations and other hydraulic parameters for (1) the current City study, (2) Shadow Woods Estates existing conditions, and (3) Shadow Woods Estates with proposed fill. COTTONWOOD CREEK City of Coppell, Texas SUMMARY TABLE 100-YEAR ULTIMATE DISCHARGE CROSS SECTION NUMBER 9526 CURRENT CITY W.S. VCH 480.58 13.02 EXTENDED EXISTING W.S. VCH 480.58 13.02 VOL. PROP. RECLAMATION W,S, 480.58 VCH 13.02 VOL. SANDY LAKE ROAD BRIDGE 9590 10120 10210 10470 10655 10780 10830 11030 11230 11330 11380 11880 12420 12540 12585 483.99 484.87 487.37 487.51 489.55 489.50 1.93 10.75 5,21 5.09 11.37 12.22 483.99 483.67 484.20 485.71 486.37 486.87 487.94 488.51 488.56 489.80 491.72 492.48 492.08 1.93 9.14 1063 10.09 1065 7.67 1074 7.72 1080 8.84 1086 6.33 1093 4.36 1105 5.77 1114 7.65 7.90 6.33 9.78 483.99 483.67 484.20 485.71 486.22 486.71 487.76 488.37 488.41 489.75 491.71 492.47 492.07 1.93 9.14 10.09 6.98 7.56 8.71 6.53 4.34 5.96 7.72 7.91 6.33 9.78 1063 1065 1074 1080 1086 1092 1104 1113 STATE 12615 12675 14600 17970 489.77 492.07 496.43 506.40 11.84 6.80 5.46 11.42 492.18 493.85 496.48 506.40 ROAD BRIDGE 492.17 I 9.77 493.85 4.99 496.48 5.40 506.40 '11.42 4.0 HEC-2 HYDRAULIC MODELS Two continuous floodway backwater models are attached. The first ts a duplication of the current effec- tive FIS floodway model obtained from Kimley-Horn and Associates, Inc. The second model represents the extended existing conditions with added cross sections for a revised floodway model. The methodology and parameters for the revised floodway model are consistent with the effective FIS. The floodway ties into the effective floodway d~)wnstream and upstream of the project area without. causing surcharges in excess of one foot above the base flood elevation. These floodway computer runs are numbers 7,4 and 7,5, respectively, 5.0 CONCLUSIONS Shadow Woods Estates is proposing to begin construction as shown on Exhibit 6. The City of Coppell Cottonwood Creek Study has established two-year ultimate, 100-year ultimate, and 100-year existing discharges and corresponding water surfaces at this location, This study expands the current effective study by adding additional cross sections to define the proposed improvements along Cottonwood Creek, The attached maps (Exhibits 3 and 6) delineate the two- and 100-year flood boundaries, the 100- year floodway boundary, and the location and alignment of cross sections and flowline used in the hydraulic model. Exhibits 4 and 5 are plots of the water surface profiles and the stream cross sections, This study demonstrates that this project is in compliance with the current floodplain criteria for the City of Coppell and FEMA.