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Copperstone FS-CS 900222 Federal Emergency Management Agency W~hington, D.C. 20472 iO~G:'~ ~B 22 I~0 The Honorable Mark Wolfe Case No.: 89-06-31R 4 ~ Mayor of the City of Coppell Co--unity: City of Coppell, P.O. Box 478 Dallas County, Coppell, Texas 75019 Texas Co,unity No.: 480170 Dear Mayor Wolfe: mis is in reference to a ~ebr~ _r~ 4~_1989 letter from Mr. Russell R. Doyle, P.E., City Engineer for the City of Coppell, concerning the Flood Insurance Study (FIS) for your co~_unity. In his letter, which was forwarded to us by our Region VI office, Mr. Doyle requested Gat the Federal Emergency Manage- ment Agency (FEMA) issue a conditional Lette~ of Map Revision (~) for the proposed ~_Boulevard___~ri_~dge and floodplain modification project along Denton Creek and Cottonwood Branch within the Parks of Coppell Subdivision. mis proposed project involves the placement of fill in the south overbank within the Parks of Coppell Subdivision property limits along Denton Creek, the placement of fill in the north overbank within the Parks of Coppell Subdivision along Cottonwood Branch, and the construction of the Parkway Boulevard Bridge and associated channel modifications across Cottonwood Branch. Ail fill is proposed outside the regulatory floodway; however, the ~b~idg~n~.-~h~...~!~a~°os..wi~.~P~r99c~ ~P0~ the regu~p~y f~P.9~. With his letter, Mr. Doyle submitted a technical rep0~--~pared by Jerry Parch~ Consulting Engineers entitled Floodplain Reclamation Study on ' Cottonwood Branch and Denton Creek for Floodplain Reclamation and Construction of Par~ay Boulevard Bridge, dated February 1989. This report contained a description of the project, HEC-2 hydraulic models representing existing and proposed conditions for the lO0-year flood and regulatory floodway for Denton Creek and Cottonwood Branch, and maps delineating the 100-year floodplain and regulatory floodway for existing and proposed conditions. With a~M~llg~ 5~ 1989 ~, Mr Doyle submitted an updated version of the technical report prepared by Jerry Parch~ Consulting Engineers to reflect changes as requested in our July 3, 1989 letter to you. Also submitted at- that time were plans p~:epared by Jer~ ParchA Consulting Engineers entitled Parks of Coppell, West of Denton Tap Road, CreeR Cross Sections, Floodplain Reclamation Stu~, dated September 1, 1989. ..... ~.~S~.~p.~a~.9~p~K~.~.~ w~th our technical evaluation contractor, Mr. Jerry Parch~, P.E., submitted revised HEC-2 hydraulic models for Cottonwood Branch representing existing and proposed conditions for the lO0-year flood and regulatory floodway. With these updated models, Mr. Parch~ submitted revised plotted cross sections for the proposed Cottonwood Branch conditions, dated October 11, 1989. ~kFees necessary to process this condi- tional LO~ (a total of $1,500) have been received ~entl~,~a revised~FIS and Flood Insurance Rate Map F~> are being ~ p~~or the City of Coppell, hereinafter referred to as the preliminary FIS and FIRM. The preliminary FIS and FIRM, which will be based upon a comprehensive restudy of all the community's streams prepared by Kimley-Horn and Associates, Inc., will be sent to the community for review approximately two months after all data requested in our December 7, 1989 letter to you is Submitted[ The preliminary FIS and FIRM w~OO-~e~ar) Flood Elevations (BFEs) and Special Flood Hazard Areas (SFHAs) in the vicinity of the proposed project. It was therefore necessary for the aforementioned , proposed conditions HEC-2 hydraulic models, submitted in support of the !,, proposed Parkway Boulevard Bridge and floodplain modification project, to be ~compatible with the analyses used to develop the preliminary FIS and FIRM for the City of Coppell. ~We~ have reviewed the submit~ed technical information and determined that the ~roposed project meets the minimum floodplain management criteria of the NFIP. If the proposed Parkway Boulevard Bridge and floodplain modification project is completed as proposed, a revision to the preliminary FIS and FIRM for your community would be warranted. For Denton Creek, which involves only fill in the floodway fringe, this revision ~ould~shgw~ a reduction in the l~3_ye,~ar floodplain and regulatory floodway within the P~0j~ct a~al .... ~'~or Denton Creek would increase and decrease at various cross sections throughout the project area.---"~or~'o~o~'~r~nch, this revision would show a reduction in the 100-year floodplain and regulatory floodway within the pr~-~ject areas for Cottonwood Branch would increase and decrease at various cross sections throughout the project area. This determination is based on the 100-year flood discharges computed in the preliminary FIS for your community, and does not c_9o~s_i_~er sub~_e_~uent 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 result in increased 100-year flood elevations. Future 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 elevations in /e %~siS conditional LOMR is based on mind. mum floodplain management criteria =ablished 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 required by Federal ~r State law have been received. State and community officials, based on I 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 ~co~p--fe~slv-V-~--{Ioo~a-~n management criteria, these criteria take precedence \over the minimum NFIP requirements. 3 NFIP regulation S_~b~a_~ph__60.3(b)(7) requires communities participating in the Program to "a~_~ssure t~aq the flood carrying capacity within the altered or relocated portion of any watercourse is maintained." nanc~ef, such as the regular clearing of a channelized stream, channel modifica- tion projects will, in time, fail to function as designed, thereby recreating the flood hazard that they were intended to mitigate. Therefore, upon completion of the project, your community must uphold its responsibility for assuring that the modified channel is maintained in order to preserve its design function. Please be aware that FEMAmay request that yo~O~ity submit a descr~iPtion and schedule of the channel maintenance activities /~the requirements for floodway revisions as outlined in NFIP regula- t~zon~ubparagraph 65.7(b)(1) (copy enclosed), which states that when a ifloodway change is propost~d,~ a~ copyco o~_~ aof a~-~ub 1 i¢,pu~ notice distributed__ ,by the community stating the community's intent to r-~-i~e--~~~way, or a state- ment by the community that it has notified all affecte~_~,o~rty owners and affected adjacent jurisdictions, must be ~b~iit-g~-i~'~E-ka-. This req-~irement must be addressed when requesting a map revision to reflect the effects of the completed Parkway Boulevard Bridge and floodplain modification project. We remind you that fill placed to raise the ground surface to or above the BFE in order to gain exclusion from an SFHA (100-year floodplain) must meet the criteria of NFIP regulation Subparagraph 65.5(a)(6). Specifically, we require that the community's NFIP permit official or a registered professional engineer or soils engineer certify the follo~'ing: ............... That the fill has been compacted to 95 percent of the maximum density obtainable with the Standard Proctor Test method for fill pads prepared for Kesi~tia~.pr ~,~.mm~K~i.~l~~ure foundations~ that fill slopes for granular materials are not steeper than one vertical on one-and-one-half horizontal (steeper slopes must be justified); and that adequate erosion protection is provided for fill slopes exposed to moving floodwaters (slopes exposed to flows with velocities of up to 5 feet per second (fps) during the lO0-year flood nmst, at a minimum, be protected by a cover of grass, vibes, weeds, or similar vegetation; slopes exposed to flows with velocities greater than 5 fps during a 100-year flood event must, at a minimum, be protected by stone or rock riprap). Upon completion of the proposed Parkway Boulevard Bridge and floodplain modification project, your community may request a revision to the effective FIS and FIRM. The revision request must be submitted to our Region VI office and must include the data listed below: 4 Evidence of compliance with National Flood Insurance Program regulation Paragraph 65.4(b), which states that "all requests for changes to effective maps must be made in writing by the community's Chief Executive Officer (CEO) or an official desig- nated by the CEO. Should the CEO refuse to submit such a request on behalf of another party, FEMA will agree to review it only if written evidence is provided indicating the CEO or designee has been requested to do so." o "As-built" plans of the Parkway Boulevard Bridge and floodplain modification project, certified by a registered engineer. o Revised HEC-2 hydraulic analyses and floodplain mapping if the "as-built" condition deviates from the proposed condition. Evidence of compliance with NFIP regulations Subparagraphs 65.7(b)(1) and 65.5(a)(6), as previously discussed. We have enclosed a copy of Part 65 of the NFIP regulations, which further describes the nature and extent of the material needed to support a request to revise an effective FIS and FIRM. Compliance with the criteria outlined in this document will expedite FEMA's review process, thus allowing the effective FIS and FIRM 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 Matthew B. Miller of our Headquarters staff in Washington, D.C., at (202) 646-3461. Sincerely, C~f~,L'R'Mlsa~t~ku~ies Division Federal Insurance Administration Enclosure cc: Mr. Jerry Parch~, P.E. ~ Ron Morrison, P.E., Kimley-Horn and Associates, Inc.