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Mansions Phase 1-CS 980210"/ Federal Emergency Management Agency Washington, D.C. 20472 FEB 1 0 1998 CERTIFIED MAIL IN REPLY REFER TO: RETURN RECEIPT REQUESTED Case No.: 98-06-303R The Honorable Candy Sheehan Community: City of Coppell, Texas Mayor, City of Coppell Community No.: 480170 255 Parkway Boulevard Coppell, Texas 75019 104 Dear Mayor Sheehan: This responds to a request that the Federal Emergency Management Agency (FEMA) comment on the effects that a proposed project would have on the effective Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FIS) report for your community in accordance with Part 65 of the National Flood Insurance Program (NFIP) regulations. In a letter dated November 17, 1997, Mr. Rusty Spiars, P.E., Vice President, Dunaway Associates, Inc., requested that FEMA evaluate the effects that proposed placement of fill, grading, and excavation of two ponds associated with the Mansions on the Lake development along Denton Creek from approximately 2,570 feet downstream to approximately 540 feet downstream of State Highway 121 (SH121) would have on the flood hazard information shown on the effective FIRM and FIS report. In addition, this request incorporates more detailed topographic information from approximately 3,840 feet downstream to approximately 540 feet downstream of SH 121 and a recently constructed pond located just downstream of the proposed project. All data required to complete our review of this request for a Conditional Letter of Map Revision (CLOMR) were submitted with letters from Mr. Spiars. Because this CLOMR request also affects the City of Lewisviile, a separate CLOMR for that community was issued on the same date as this CLOMR. We have completed our review of the submitted data and the flood data used to prepare the effective FIRM for your community. The submitted existing conditions HEC-2 hydraulic computer model, dated January 6, 1998, based on updated topographic information, was used as the base conditions model in our review of the proposed conditions model for this CLOMR request. We believe that, if the proposed project is constructed as shown on the submitted topographic work map entitled "Floodplain Map, Mansions on the Lake," dated January 8, 1998, and the submitted report entitled, "Application for Conditional Letter of Map Revision for the Mansions on the Lake, Denton Creek, Coppell, Texas," dated June 1997, both prepared by Dunaway Associates, Inc., and the data listed below are received, a revision to the FIRM would be warranted. As a result of the addition of more detailed topographic data, the corrected effective conditions elevations of the flood having a l-percent chance of being equaled or exceeded in any given year (base flood) decreased compared to the effective base flood elevations (BFEs) along the revised reach. The maximum decrease in BFE, 0.2 foot, occurred approximately 1,490 feet downstream of SH121. As a result of the addition of an existing pond just downstream of the proposed project, the existing conditions BFEs decre~ed compared to the corrected effectzve conditions BFEs. The maximum decrease in BFE, 1.6 feet. occurred approximately 2,570 feet downstream of SH121. As a result of the proposed grading, pond excavation, and placement of fill within the revised reach, the BFEs will decrease compared to the existing conditions BFEs. The maximum decrease in BFE, 0. I foot, will occur approximately 1,340 feet downstregm of SH 121. The BFEs will decrease compared to the effective BFEs along the revised reach as a result of the proposed project. The maximum decrease in BFE, 1.6 feet, will occur approximately 2,750 feet downstream of SH 121. Thc widths of the Special l~lood l-lazard Area (SFHA), the area that would be inundated by the base flood, and the regulator3' floodway will decrease compared to the effective SFHA and floodway widths. Upon compIetion of the project, your community may submit the data listed below and request that we make a final determination on revising the effective FIS report and FI1LM. Effective October 1, 1996, FEMA revised The fee schedule for reviewi,~g and processing requests for co~ditional and final modifications to published flood information and maps FEMA established fiat review and processing fees [or most types of requests. Effective March 10, 1997, FEMA modified the fee schedule that became effective on October 1. In accordance with this schedule, the fee for your map revision request will be $2,300 and must be received before we can begin processing ,,,'our request. Payment of this fee shall be made in the form of a check or money order, made payable in U.S. funds to the National Flood Inglrance Program, or by credit card. The payment must be forwarded to the following address: Federal Emergency Management Agency Fcc-Collection System Administrator P.O Box 3173 Merrifield, VA 22116-3173 · As-built plans, certified by a registered professional engineer, of all proposed project elements ~ · Co~'t:u'nunity acknowledgment of the m~p revision request Certification that all fill placed in the currently effective base floodplain and below the proposed BFE is compacted to 95 percent of the maximum density obtainable with the Standard Proctor Test method issued by the American Society for Testing and Materials (ASTM Standard D-698) or an acceptable equivalent method for all areas to be removed from the base floodplain -~ * A cop)' of thc public ~otice distributed by your cornmuni~' stating )'our conm~unity intent to revise tl~e floodway, or a statement by your co~,ca~-~unity that it has notified all affected property owners and affected adjacent jurisdictious ~'~'["]'- % * A letter stating that 3,'our conununiD' will adopt and enforce the modified floodway The base floodplain topwidths shown in the revised proposed hydraulic analysis do not match the approximate base floodplain topwidths shown on the above-referenced topographic work map at the following cross sections. HEC-2 Model Topographic Map Cross Sectton _ (feet'} (~eet:, 35700 2,046 1,700 36250 1,300 1,650 36970 655 1.300 39440 724 980 394.90 523 1,000 Please provide an explanation for these discrepancies, or make the appropriate changes. Hydraulic analyses, for as-built conditions, of the base flood, the flood having a 0.2-percent chance of being equaled or exceeded in any given .,,'ear, and regulatory floodway if they differ from the proposed conditiox~s models After receMng appropriate documentation to show that the project has been completed. FEMA will initiate a revision to the FIRM and FIS report. Because the BFEs would change as a result of the project, a 90-day appeal period would be initiated, during which communib' officials and interested persons may appeal the revised BI=Es based on scientific or technical data. The basis of tins CLOMR is, in whole or in part, a cham~el-modification project. NFIP regulations, as cited in Parag[aph 60.3(b)(7), require that conunumties assure that the flood-carrying capac[b' within the altered or relocated portion of any watercourse is mamtained. This provision is incorporated into your community's existing floodplain management regulations. Consequently. the ultimate responsibility for maintenance of the modified channel rests with 5'our co~lllnunit3'. This CLOMR is based on minimum floodplain ma~xagement criteria established under the NFIP. Your conm'mnib' is responsible for approving all floodplain development, and for ensuring all necessary permits required by Federal or State law have been received. State, county, and conmmnity officials, based on knowledge of local co~dmons and in the interest of safety, may set h,gher standards for construction in the SFHA. If the State, county, or conmaunity has adopted more restrictive or comprehensive floodplain management criteria, these criteria take precedence over the minimum NFIP criteria. 4 If you have an,,,' questions regarding floodplain management regulations for your communit'y or the NFIP in general, please contact the Consultation Coordination Officer (CCO) for your community. Information on the CCO for your conm-tunity may be obtained by contacting the Director, Mitigation Dwision of FEMA tn Denton, Texas, at (940) 898-5127. If you havc any technical questioT~q regarding this CLOMR, please contact Mr. Alan lolmson of our staff in Washington. DC, either by telephone at (202) 646-3403 or by facsimile at (202) 646-4596. Sincerely, ~,. Frederick H. Sharrocks, Jr., Chief .... Hazard Identification Branch Mitigation Directorate cc: The Honorable Bobble Mitchell Mayor, City of Lewisville Mr. Kenneth .,'%{. Griffin, P.E. Director of Engineering City of Coppelt Mr. T. S Kumar Assistant City Engineer City of Lewisville Mr. Rust,, Spears, P.E. Vice P....:dent Dunaway Associates, Inc. bce. Regional Director R6-MT MT-HZ-ID Chron MT-HZ-ID MBJ Case File/MSMILDB;BMS/3206.cs MBJ Project y,~,~./, "'.~ Concurrences: M-i4- I~Z-1D NIT-HZ-ID Johnson . Mohr ; .,-{: ?..