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Creekview North-CS 880701Federal Emergency Management Agency W. ashington, D.C. 20472 The Honorable Lou Duggan Mayor of the City of-Coppell P.O. Box 478 Coppell, Texas 75019 Dear Mayor Duggan: RECEIVE JtlL 1 5 NATHAN O. MAIER CONSULI'IN6 ENGINEERS No~ 88-06~-37R This is in reference to a February 2, 1988 letter from Mr. H. Wayne Ginn, P.E., City Engineer and Floodplain Administrator for the City of Coppell. In his letter, which was forwarded to us by our Region VI office, Mr. Ginn requested that the Federal Emergency Management Agency (FEMA) issue a con- ditional Letter of Map 'Revision (LOMR) for the Creek View Addition project. This project consists of channel modifications to Grapevine Creek between Moore Road and Denton Tap Road. With his February 2, 1988 letter, Mr. Ginn submitted a technical report prepared by Nathan D. Maier Consulting Engineers, Inc., entitled Floodplain Reclamation Study for the Creek View Addition Along Grapevine Creek, dated November 1987. This report included the following technical data: HEC-2 hydraulic models, dated November 10, 1987, representing existing conditions; HEC-2 hydraulic models, dated January 16, 1988, repre- senting proposed conditions; a Floodplain Reclamation Plan, dated January 1988; cross-sectional information for Grapevine. Creek; and a flood profile for Grapevine Creek. Following a May 11, 1988 telephone conversation with our technical evaluation contractor, Mr. Dennis L. Johnson, P.E., of Nathan D. Maier Consulting Engineers, Inc., submitted additional H~C-2 hydraulic models, dated May 18, 1988, representing both existing and proposed conditions. ! Based on our review of the submitted technical data, we have determined that the proposed Creek View Addition project meets the minimum floodplain management criteria set forth by National Flood Insurance Program (NFIP) regulations. If the project were completed as proposed, a revision to the effective Flood Insurance Study (FIS), Flood Insurance Rate Map (FIRM), and Flood Boundary and Floodway Map (FBFM) for your community would be warranted. This revision would show a decrease in the Base (100-year) Flood Elevations and the lO0-year floodplain of Grapevine Creek; however, there would be ho change in the floodway width, as indicated in the submitted hydraulic calculations. Please note that future revisions to your community's FIS, FIRM, and FBFM or future restudies of the flood hazards in this area could modify this determination. This determination is based on the 100-year flood discharges computed in the · effective FIS for your community, and does not consider subsequent changes in watershed characteristics that would tend to increase flood discharges.- The development of this project and other projects upstream could result in increased flood discharges, which, in turn, could resultin increased 100-year flood elevations. F~ture restudies of your community's flood hazards would take into account the cumulative effects of development on flood discharges, and could therefore establish higher 100-year flood elevat/ons in this area. 2 This conditional LOMR is based on minimum floodplain management' criteria established under the NFIP. Your community is responsible for ,approving all proposed floodplain developments, including the project upon which this request is.based, and for assuring that necessary permits requir.ed 'by Federal or State law have been received. State and community officials, based on knowledge of local conditions and in the interest of safety, may set'higher standards for construction or may limit development in floodplain areas. If the State of Texas or the City of Coppell has adopted more restrictive or comprehensive floodplain management criteria, these criteria take precedence over the minimum NFIP requirements. NFIP regulation Part 60.3(b)(7) requires communities participating in the Program to "assure that the flood carrying capacity within the altered or relocated portion of any watercourse is maintained." Without proper mainte- nance, such as the regular clearin~ of a channelized stream, channel modifi- cation projects will, in time, fail to function as designed, thereby recreating the flood hazard that they were intended to mitigate. Therefore, upon com- pletion of the project, your community must uphold its 'responsibility for assuring that the modified channel is maintained in order to preserve its design function. Upon completion of the proposed Creek View Addition project, your community may request a revision to the effective FIS, FIRM, and FBFM. The revision request must include supporting data outlined in the enclosed copy of Part 65 of the NFIP regulations. Please note that these supporting data must represent the conditions of the area as they exist at the time the request is submitted. Compliance with the criteria outlined in the aforementioned regulations will expedite FEMA's review process, thus allowing the effective FIS, FIRM, and FBFM for your community to be revised as appropriate, in.a timely manner. Should you have any questions regarding this matter, please do not hesitate to contact the Chief, Natural and Technological Hazards Division of the Federal Emergency Management Agency in Denton, Texas, at (817) 898-9127 or members of our Headquarters staff in Washington, D.C., at (202) 646-2754. Sincerely, C~, Risk Studies Division Federal Insurance Administration Enclosure cc: Mr. H. Wayne Ginn, P.E. Mr. Dennis L. Johnson, P.E.