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DR9502-CS 960401Ill Halff Associates ENGINEERS · ARCHITECTS · SCIENTISTS PLANNERS · SURVEYORS 8515 NORTHWEST PLAZA DRIVE DALLAS, TEXAS 75225 (214) 739-0094 FAX (214) 739-0095 April 1, 1996 AVO 15254 Mr. Kenneth M. Griffin, P.E. Assistant City Manager/Director of Public Works City of Coppell 255 Parkway Blvd. Coppell, Texas 75019 Re: Andrew Brown Jr. Park West Hydraulic Study. Dear Mr. Griffin: Attached are preliminary results for the Andrew Brown Jr. Park (West) Hydraulic Study. You will find a l l"x17" basemap of the site, 2 cross-section plots showing proposed versus existing condition topography, a comparison table of water surface elevations and hard copies of the hydraulic models output. The Denton Creek hydraulic models are as follows: 1. FIS effective model: DCMODZ.dat 2. Revised existing condition model: RVEXDC.dat 3. Revised (proposed) condition model: PROPDC.dat Cross-sections 32725 and 33145 were revised in model RVEXDC.dat to reflect the new City of Coppell topographic mapping. The PROPDC.dat model reflects the proposed park improvements (minor grading and parking lot paving). Please note that our review of the FIS effective model turned up several inconsistencies upstream and downstream of the project site. However, these problems affect revised existing conditions and proposed conditions equally. Therefore, the results of this hydraulic study are not impacted and the inconsistencies were not corrected in the computer models. Hydraulics, basemap preparation and pre-construction surveys of the site are essentially complete and we are ready to proceed with appropriate submittals to the Federal Emergency Management Agency (FEMA), subject to your review and approval. Because no flood plain reclamation occurs on the site (no change in flood plain mapping) and base flood elevations are essentially unchanged for the proposed conditions, the FIS FIRM map and profile do not need to be revised and a Conditional Letter of Map Revision (CLOMR) application is not required by FEMA. Instead, a letter certifying the results of the hydraulic study can be prepared and placed in the files of the flood plain administrator. FEMA refers to this process as "no rise" certification. This no rise certification and report should also be forwarded to the regional and headquarters offices of FEMA. This procedure was confirmed in a phone conversation with Jack Quarles of FEMA Region VI. DALLAS · FORT WORTH · HOUSTON · ARLINGTON · McALLEN · CHICAGO TRANSPORTATION · WATER RESOURCES · LAND DEVELOPMENT · MUNICIPAL · ENVIRONMENTAL · STRUCTURAL MECHANICAL · ELECTRICAL · SURVEYING · GEOGRAPHIC INFORMATION SYSTEMS ARCHITECTURE · LANDSCAPE ARCHITECTURE · PLANNING II ..l Halff Associates lll ENGINEERS · ARCHITECTS · SCIENTISTS PLANNERS · SURVEYORS Exceptions to this "no rise" certification process could be as a result of local flood plain ordinances with more stringent requirements. For example, if the City of Coppell's flood plain ordinance requires FEMA approval for any flood plain activity, then the CLOMR application may still be required. West. Of course, map amendment ~ required. Please call me at your reviewed this package. In summary, application for conditional and final LOMR may not be required for Andrew Brown Park pplications for the Service Center and Senior Citizen Center are still earliest convenience to discuss a plan of action when you have Sincerely, HALFF ASSOCIATES, INC. Walter E. S . Vice President Enclosures. File: ltO40196.doc Table 1 - Andrew Brown Park West Comparison Table of 100-year Water Surface Elevations FIS Duplicate FIS Duplicate Effective Revised Existing Conditions Proposed Conditions Location DCMODZ.hc2 DCMODZ.dat RVEXDC.dat PROPDC.dat Section WSEL Section WSEL Difference Section WSEL Difference Section WSEL Difference 30027 456.38 30027 456,38 0 30027 456.38 0 30027 456.38 0 30384 456.74 30384 456.74 0 30384 456.74 0 30384 456.74 0 30604 '~ 457.42 30604 457.42 0 30604 457.42 0 30604 457.42 0 30958 457.93 30958 457.93 0 30958 457.93 0 30958 457.93 0 ~ 31335 457.83 31335 457.83 0 31335 457.83 0 31335 457.83 0 32150 457.91 32150 457.91 0 32150 457.91 0 32150 457.91 0 Denton Tap Rd Bridge 32200 457.71 32200 457.71 0 32200 457.71 0 32200 457.71 0 Denton Tap Rd Bridge 32230 457.91 32230 457.91 0 32230 457.91 0 322~0~ ,~ 457.91 0 32250 460.31 32250 460.31 0 32250 460.31 0 32250~ 460.31 0 U/S Denton Tap Road 32305 460.15 32305 460.15 0 32305 460.15 0 32305 460.15 0 32725 461.24 32725 461.24 0 32725 461.22 -0.02 32725 461.18 -0.04 33145 461.44 33145 461.44 0 33145 461.54 0.10 33145 461.50 -0.04 33470 461.72 33470 461.72 0 33470 461.67 -0.05 33470 461.65 -0.02 I !!Il 34260 462.54 34260 462.54 0 34260 462.50 -0.04 34260 462.49 -0.01 34850 462.56 34850 462.56 0 34850 462.53 -0.03 34850 462.51 -0.02 34950 463.65 34950 463.65 0 34950 463.62 -0.03 34950 463.61 -0.01 36970 465.99 36970 465.99 0 36970 465.99 0 36970 465.99 0 38200 466.71 38200 466.71 0 38200 466.71 0 38200 466.71 0 39290 466.99 39290 466.99 0 39290 466.99 0 39290 466.99 0 ' 39440 466.72 39440 466.72 0 39440 466.72 0 39440 466.72 0 - 39490 467.15 39490 467.15 0 39490 467.15 0 39490 467.15 0 39540 467.06 39540 467.06 0 39540 467.05 -0.01 39540 467.05 0 40650 468.20 40650 468.20 0 40650 468.20 0 40650 468.20 0 48000 '~ 470.69 48000 470.69 0 48000 470.69 0 48000 470.69 0 51350 472.00 51350 472.00 0 51350 472.00 0 51350 472.00 0 53350 472.57 53350 472.57 0 53350 472.57 0 53350 472.57 0 55590 473.25 55590 473.25 0 55590 473.25 0 55590 473.25 0 56940 474.50 56940 474.50 0 56940 474.50 0 56940 474.50 0 File: i:~avo\15254\h&h\exist\fis-wsel.xls 12:25:52 3/29/96 470.00 480.00 450.00 440.00 430. O0 t200.00 t400.00 ~800.00 t800.00 2000.00 2200.00 2~00.00 2800.00 Section 33:145. O0 2800.00 3000.00 3200.00 3400.00 I \\DALLAS\VOLI\AVO\t52S4\H&H\CLOMR\TEST-TOO.HRO GROUND PROFILE SECTIONS Anclrew Brown Park Heet Halff Aeeociatee. Tnc. H: ~, -,miO0 , ~ V: %"m %0 470.00 PROPOSED GROUND PROFILE 4~0.00 4~0.00 EXISTING GROUND PROFILE 440.00 4~0.00 A400.O0 tBO0.O0 tBO0.O0 2000.00 2200.00 2400.00 2BO0.O0 2900.00 I I I Sect ion 52725. O0 3000.00 3200.00 3400.00 3600.00 3900.00 I I I I \\DALLAS\VOLt\AVO\~52~4\H&H\CLOMR\TEgT--TOO.HRG Frt GROUND PROFILE SECTIONS Anclrew Brown Parl< ~est Halff AeeocAatee. ~nc. ~lla NU. H: ~, "-~00 V: ~," .,,