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Lake Park-CS 910709 Federal Emergency Management Agency o . ~ Engineering Case ~o.: 9[- 6-36[ Mr. William A. Anderson, P.E. Community: City of Coppel~, Dan M. Dowdey & Associates Dallas County, 16250 Dallas Parkway, Suite 100 Texas Dallas, Texas 752A8 Community No.: 480170 Dear ~r. Anderson: !!i This is in response to the request for a conditional Letter of Map Revision ::: (LOMR) for Lake Park Addition in the City of Coppell, Texas, dated February 8, 1991. Our March 12, 1991 letter co you re~ardinE chis request indicated chat additional data might be required to complete our review of the request. The :..: data required to complete our review is listed on the enclosure. The required data should be submitted Co the address below,'within 30 days of the date of this letter. Dewberry & Davis 8401 Arlin~ton Boulevard Fairfax, Virginia 22031 Attention: Mr. Joseph Chapman Management En~ineerins and Technical Services Division The case number referenced above should be included on any correspondence re~ardin~ the reques=. Further ac=ion on Che request has been suspended pendin§ rece£pC of che addiCtonal da=a. Please note Chat the initial fee already submitted is the minimum charge for a review of this type. Additional costs could be required upon completion of our review and prior co issuance of a conditional LOMR, dependin~ on the complexity of the required review. You will be notified of the estimated total processin§ cost if tC is anticipated that, due to the extent of the review required, the total cost will exceed $1,500. In that situation, our review would be suspended pendin~ written authorization from you to proceed. Also note that the initial fee of $560.00 already submitted will only be applied Co chis request if we receive the required additional data within 90 days of the date of this letter. After 90 days, the request will be treated as an original submittal and will be subject to all submittal/payment proce- dures, includin~ the initial fee. 2 If you have any questions concerning FEMA policy, or the National Flood Insurance Program in general, please call Hatthew B. Miller of our Head- quarters staff in Washington, D.C., at (202) 646-3461. Sincerely, William R. Locke Chief, Risk Studies Division Federal Insurance Administration Enclosure cc: The Honorable Mark Wolfe, Mayor of the City of Coppell Ms. M. Shohre Daneshmand, P.E., Acting City Engineer Mr. Ronald W. Morrison, P.E., Morrison Hydrology/Engineering, Inc. Mr. Art Whitney, Dan M. Dowdey & Associates Case No.: 91-06-36R Community: City of Coppell, Dallas County, Texas Community No.: 480170 Additional Data Required Co Support a Conditional Letter of Map Revision Request JOL 9 t991 Requescor: Mr. gilliamA. Anderson, P.E. Dace: Currently, a revised Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM), hereinafter referred Co as the preliminary FIS and FIRM, are bein~ processed for the City of Coppell. The preliminary FIS and FIRM will modify Base (lO0-year) Flood Elevations (BFEs) and Special Flood Hazard Areas (SFHAs) in the vicinity of the proposed Lake Park Addition as shown on the FIRM Chat will become effective October 16, 1991. lc Es therefore necessary for the HEC-2 hydraulic models for Denton Creek, submitted in support of the proposed Lake Park Addition, to be compared with the data used Co prepare the pre- ltmtnary FIS and FIRM in order Co ensure that the analyses used to determine potential effects on flood hazards of the Lake Park Addition are adequate and compatible with the analyses beins used Co develop the preliminary FIS and FIRM. The HEC-2 models submitted in support of this request were primarily based on the models for Den=on Creek beins used to prepare the preliminary FIS and FIRM. However, before the Federal Emersency Management Asency can complete the review of the effects of the proposed Lake Park Addition alons Denton Creek, the followin~ issues must be resolved: 1. The revised existing conditions HEC-2 models for Denton Creek contained in the submitted technical report entitled Lake Park Addition. CoDDell. Texas, which was prepared by Dan M. Dowdey & Associates, contain cross section numbers 24400 and 25770. These sections were not included in the May 1, 1990 HEC-2 models for Denton Creek prepared by Kimley-Horn and Associates, Inc. (KHA), which are being utilized Co prepare the preliminary FIS and FIRM. In order for us Co review the effects of the proposed project, three models are required: a duplicate extscins conditions model exactly dupltcacins the input data from the May 1, 1990 KHA models, a revised existins conditions model tncorporaCin~ the additional cross sections (24400 and 25770) through the project area, and a proposed conditions model represenCin~ the proposed project. Therefore, co complete the data necessary Co support this request, models exactly duplicacin~ the input from the Hay 1, 1990 KHA models must be submitted. 2. Also, in the revised existing conditions HEC-2 models contained in the submitted report, the lO0-year natural water-surface eleva- tions at cross section numbers 29610 and 30570 from the 10-, 50-, 100-, and 500-year (multiple profile) run do not match the 100- year unencroached water-surface elevations from the floodway run. The multiple profile model and floodway model should be revised so that the 100-year water-surface elevations agree at every cross section. 3. The proposed fill associated with the Lake Park Addition will not encroach in the floodway for Denton Creek that will be shown on the preliminary FIP, H, but does encroach into the current regula- tory floodway. However, the associated proposed improvements to the existing lake upstream of the Lake Park Addition will encroach into both the preliminary and regulatory floodways. This en- croachment results in 100-year water-surface elevation increases of 0.02 foot at cross section number 25770 and 0.22 foot at CROSS section number 26830, when compared to the revised existing conditions models. ~hen proposed encroachments within the floodway result in any increase in flood levels of the base (100- year) flood, the following items must be submitted, in accordance with Section 65.12 of the National Flood Insurance Program (NFIP) regulations. o an evaluation of alternatives that would not result in a BFE increase, demonstrating why these alternatives are not feasible; o documentation of individual legal notice to any property owners impacted by the increased BFEs; and o certification that no structures insurable under the NFIP are located in areas that would be impacted by the increased BFE. In lieu of submitting the above items in accordance with Section 65.12 of the NFIP regulations, your project may be revised so that the proposed 100-year water-surface elevation increases are eliminated, if this option is pursued, HEC-2 models representing the revised project showing no increases in the 100-year water- surface elevation when compared to the revised existing conditions model must be submitted.