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ST8502-CS 880929-Kimley. Horn and Associates, Inc. 12660 Coit Road. Suite200. Dallas. Texas75251 .(214)386-7007 Raleigh, Charlotte, Naahvile, Virginia ~ach, Washinglon. Dallas, Phoenix. September 20, 1988 WeslPalmBeach. Tampa. Orlando, Ft.l. audetdale. VeroBeech, Ft. MyerslStUarl Mr. John Karlsruher, P.E. Ginn Inc. 17103 Preston Road Suite 100 Dallas, Texas 75248 Re: Response to FEMA letter regarding Moore Road Bridge. Job No. 9183.01 Dear Mr. Karlsruher: We received the attached FEMA letter on September 26 and called FEMA the next day to clear up this problem. We discussed the matter with Mr. Dave Loshbaugh, a FEMA Technical Consultant. Mr. Loshbaugh then contacted Mr. Matt Miller, FEMA Project Officer and Mr. John L. Matticks, FEMA Chief, Risk Studies Division. They have all agreed to allow the Moore Road project without additional modification if the following is provided to FEMA: A letter from the City of Coppell stating that the location of the apparent violation (cross section 18600) is owned by the City of Coppell, and that the City approves the approximate one half foot increase in the floodway elevation. 2. A modification to the floodway at this location showing the floodway at the same width as the floodplain. 3. A set of construction plans for tile Moore Road Bridge certified "as- built" b7 a registered professional engineer. A set of construction plans for the Northlake Woodlands East development, located approximately 2,000 feet downstream of the Moore Road Bridge certified "as-built" by a registered professional engineer. Building client relationships since 1967 Mr. Karlsruher, P.E. September 29, 1988 Page Two We have prepared a draft letter (attached) that we feel would be appropriate for the City of Coppell to send as a response to the subject FEMA letter. If you need additional information, please call me. Sincerely, KIMLEY-HORN AND ASSOCIATES, INC. Ronald W. Morrison, P.E. Senior Hydrologist Attachments: September 22, 1988 FEMA letter, Draft FEMA response CERTIFIED MAIL RETURN RECEIPT REQUESTED Federal Emergency Management Agency Washington, D.C. 20472 1A-PA-RS {100) The Honorable Lou Duggan Mayor of the City of Coppell P.O. Box 478 Coppell, Texas 75019 Dear Mayor Duggan: SEP 2 6 i U8 Dallas, Texa~ Please find enclosed two preliminary copies of the revised Flood InSurance Study (FIS) and Flood Insurance Rate Map (FIRM) for the City of Coppell, Dallas and Denton Counties, Texas. We have completed our technical evaluation of the available data and have incorporated the appropriate changes into the enclosed copies. This preliminary FIS and FIRM revision is primarily based on the updated hydrologic and hydraulic analyses for the Elm Fork of the Trinity River prepared by the Fort Worth District U.S. Army Corps of Engineers and completed in October 1 986. These analyses result in an increase in the Base (100-year) Flood Elevations (BFEs), and a modification to the floodway and the 100- and 500-year floodplain boundaries for the Elm Fork of the Trinity River for its entire length within the community. Also note that the BFEs for the extreme downstream reaches of Denton Creek and Grapevine Creek have increased as a result of the higher backwater elevations from the Elm Fork of the Trinity River. The updated hydraulic analysis for Denton Creek downstream of Denton Tap Road prepared by DannenbaUm Engineering Corporation in February 1985 has also been incorporated into this preliminary FIS and FIRM revision. This analysis was used in the preparation of the FIS and FIRM for the contiguous community, the City of Lewisville. This analysis has resulted in a decrease in the BFEs, floodway, and the 100- and 500-year floodplain boundaries for the affected portion of the stream. In addition, this preliminary FIS and FIRM revision includes map changes reflecting previously issued Letters of Map Revision: (1) April 4, 1985 - floodway modification along the Elm Fork Of the Trinity River for a develop- ment referred to as the Lakes of Coppell; (2) January 21, 1986 - Irving Flood Control District, Section III levee and channel modifications along the Elm Fork of the Trinity River and Grapevine Creek; (3) May 23, 1986 - fill and channel modification project along Cottonwood Branch downstream of Sandy Lake Road; and (4) September 24, 1987 - channel and floodplain modification project along Denton Creek between Denton Tap Road and DeForest Road (Parks of Coppell)- If you have any comments that might justify modifying the results described above, please use one copy of the enclosed map to identify the area of concern and return it to us within thirty calendar days from the date of this letter. If you are in agreement with our findings, please respond with a letter stating that you have reviewed the accompanying material. 2 In a letter dated November 30, 1987, from Mr. H. Wayne Ginn, P.E., former City Engineer and Floodplain Administrator for the City of Coppell, we were asked to revise the FIS for Coppell to incorporate the effects of the new Moore Road bridge across Grapevine Creek. Substantiating documentation for the request consisted of a technical report prepared by Kimley-Horn and Associates, Inc., entitled, Floodplain Hydraulics Study, Grapevine Creek, Moore Road Bridge Replacement, City of Coppell, Texas, dated 1987. Our review of the submitted data indicates that, in general, the project results in a decrease in flood elevations. However, immediately upstream of the new bridge, higher 100-year water-surface elevations result from the new construction in the floodway. This constitutes a violation of the National Flood Insurance Progra? regulations regarding regulatory floodways. Pending resolution of this apparent violation, we will not revise the FIS and FIRM to reflect the Moore Road bridge project. As soon as it is resolved, we will forward a revised preliminary FIS and FIRM to you for review which does include the effects of the Moore Road bridge replacement over Grapevine Creek. The violation exists at cross section 18600 and is outlined in the water- surface elevation (WSEL) table below: Baseline model (ft.)* Floodway WSEL lO0-~ear WSEL Cross section 465.55 466.57 18600 (just upstream of Moore Road bridge) *Referenced to the National Geodetic Vertical Datum of 1929 "As-Built" model (ft.)* 100-~ear WSEL Floodway WSEL 466.06 467.05 The floodway WSEL computed in the baseline model, 466.57, is one foot higher than the 100-year WSEL and therefore reflects the maximum WSBL that can be permitted to occur at cross section 18600 as a result of development. The "as-built" 100-year WSBL of 466.06 is lower than this maximum value; therefore, it is within acceptable limits. However, the "as-built" floodway model would permit a new maximum WSEL of 467.05; this is not allowable. To resolve the problem, either a physical remedial action should be performed, such as an offsetting channel modification, or the floodway must be widened so that the "as-built" floodway WSEL does not exceed the baseline 100-year WSEL by more than 1.0 foot at any point. In addition, we have identified the following concerns, which must be resolved before a revision can be performed: o The aforementioned construction plans for the Moore Road bridge prepared by Ginn Inc., need to be certified "as-built" by a registered professional engineer. These plans must be submitted for review. o "As-built" plans for the Northlake Woodlands East development, located approximately 2,000 feet downstream of the Moore Road bridge, certified by a registered professional engineer, were not included with this request. This information must be submitted for review. Our Region VI office will contact you to discuss this matter and achieve a resolution of the apparent violation. At that time, we will make appropriate changes to the Grapevine Creek flooding analysis. If you have any questions, please contact the Chief, Natural and Technological Hazards Division of the Federal Emergency Management Agency, in Den6on, Texas, at (8~7) 898-9]27 Or Matthew B. Miller of our Headquarters staff at (202) 646-3461. Sincerely, Ch~f, Risk Studies Division Federal Insurance Administration Enclosures cc: Mr. Russell Doyle, City Engineer, City of Coppell Mr. Ervin A. Meyer, P.E., Nathan D. Maier, Inc. Mr. Ronald Morrison, P.E., Kimley-Horn and Associates, Inc. Mr. Jerry Parche, P.E.