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St Andrews Est-CS04060306/03/04 THU 15:27 F~ 97223~3820 DALLAS ~002 Kimley-Horn and Associates, Inc. June 3, 2004 Mr. Kenneth M. Griffin, P.E. Director of Engineering and Public Works City of Coppell 255 Parkway Boulevard Coppell, TX 75019 Re: Review of CLOMR Request on Old Denton Creek St. Andrews Estates City of Coppell~ Texas KHA No. 063124006 Dear Ken: We have completed our review of the referenced Conditional Letter of Map Revision (CLOMR) request for the proposed subdivision. The following comments are based on the requirements outlined in the City of Coppell Drainage Manual and Federal Emergency Management Agency (FEMA) criteria. Comments are in no particular order and should be addressed by number. KHA recommends that: This report appears to be a combination of two submittals to FEMA. The first submittal is a Letter of Map Revision (LOMR), the purpose of which would be to correct a mapping error on the effective FIRM. The second submittal is a Conditional Letter of Map Revision based on Fill (CLOMR- F). The CLOMR-F submitlal would be based on the proposed filling of the finger of the floodplain that extends into the subject tract. These submittals should be separated and delivered to FEMA as two requests. LOMR and CLOMR-F requests are reviewed by different groups at PBS&I. Please be advised that revisions requested in a CLOMR-F submittal cannot result in alteration of the floodway. Therefore, the LOMR submittal will have to be accepted by FEMA prior to the CLOMR-F. The floodplain elevation tables located in Appendix G show an increase in the 100-year floodplain elevation fi'om existing to proposed conditions at cross sections 24700, 23800, and 23700. The location of the proposed fill appears to be in a possible ineffective flow area. If the proposed fill will affect the regulatory 100-year floodplain elevation, then a CLOMR should be performed, not a CLOMR -F. Revise the modeling to avoid the revision to the floodplain elevation, or revise the submittal to meet the requirements for a CLOMR. 7525! · TEL 972 770 1300 FAX 972 239 --. 06/03/04 THU 15:27 FA~ 9722393820 DALLAS ~003 and Associates, Inc. Mr. K~nm~h M. Griffin, P.E., J~u~ 3,2004, Pmge 2 The Property Information Form states that the CLOMR-F request is for a single lot. The final plat included in the submittal shows that the floodplain reclamation occurs over six lots. If this plat has been filed, then the forms should be revised to state that the request is for multiple lots. If the plat has not been filed, then the current plat should he included in the report. The Property Information Form states that the entire legally recorded properly is to he removed from the floodplain. The final plat appears to show that portions of Lots 16 and 17 will remain in the floodplain. The May 14, 2004 letter to Kaith Marvin included a metes and bounds for the area remaining in the floodplain. However, the CLOMR-F instructions require a metes and bounds description of the area to be removed from the floodplain. This metes and bounds description should be included with the CLOMR-F submittal. Thc Elevation Form states that the elevation datum for the survey is NAD 82. NAD 82 is a horizontal datum. Please revise the form to state the vertical datum for thc survey. The vc~ical datum used for the FEMA modcling in Dallas County is NG%rD 29. If the datum used in this CLOMR-F is different, please state the conversion factor. The Riverine Hydrology & Hydraulics Form states that all of thc effective, pre-project, and post-project models can be found in StAndrews.pt~, which is included on the attached floppy disk. When this model is loaded, a message appears stating that many files are missing. The plan files are not named, and it is difficult to tell which is the existing model and which is the proposed model. Finally, there arc only two plan files on the disk. Therefore, there cannot be effective, existing, and proposed conditions models. Include and label digital copies of the effective, existing, and proposed models for Denton Creek. Also include a hard copy of the effective model with thc report. A CLOMR-F submittal will not require hydraulic modeling to be submitted to FEMA, while the LOMR submittal will. However, since the purpose of the LOMR is only to revise the effective floodway delineation to reflect the intent of the 1997 LOMR, only an effcctive model will he required to be submitted to FEMA. No '~ost-project simulation" models, which model proposed conditions that have not yet been constructed, should be included in the LOMR. For the purposes of obtaining approval of this CLOMR-F fi.om the City of Coppell, the revisions requested in comments 2 and 6 of this letter must still be made and approved by the City. Thc grading plan provided is not to scale. Please provide a grading plan that is set to a measurable scale. Revise the grading plan to illustrate thc grading around the proposed beadwall and show how the floodplain will encroach on this grading. G:~'IY DRO~ROJECTS~63124006~LtrSA01 .d0~ 06/03/04 THU 15:28 FAX 9722393820 DALL~.S ~004 and Associat6s, inc. Prodde the proposed flow velocity exiting the headwall during the 100-year event and detail the erosion control measures proposed at the headwall. 11. The floodplain work map shows that the floodplain width at cross section 23500 is approximately 120-feet wide, while the proposed condition table in Appendix G states that the floodplain width is over 4000-feet. This discrepancy occurs with evexy cross section on the work map. Revise the modeling and the workmap to have consistent floodplain widths. 12. The floodplain workmap does not appear to reflect the topographic information upon which the cross s~tions in the HEC-RAS modeling were based. Wherever possible, include the topographic information from the modeling on the floodplain wurkmap. 13. The May 14, 2004 letter to Keith Marvin states that the cross section lines should be considered schematic, and that the cross sections arc meant to be perpendicular to the flow along Old Denton Creek. The floodplain workmap should be revised to reflect this intent, and should not bc drawn schematically. The above comments should bc addressed, and thc CLOMR request should be formally submitted for a second review. If you have any questions or comments, please do not hesitate to call. Sincerely, K1MLEY-HORN AND ASSOCIATES, INC. Project Manager cc: I. David Evans, P.E. - Evans Engineering GAHYDRO~PROJECTS~63124006~LtrSA01 06/03/04 THU 15:26 F~ 9722393820 DALLAS ~001 Kimley-Horn and Associates, Inc. Fax Trar~mittal Sui~ 1800 12700P~kCm~G Drive DaO~,Tex~s 7525i TEL 972~7~1300 FAX g?2~39~820 To: Original coming by mail: Yes [] Fax No,: Job No.: Dais: No [] If you have any problems, please call 972-770-1300 and ask for: This fac.ffmile is h,tended for the addressee named hereto and may contain information that £x confidential. If you are not the ~ntended recipient or the employee or agent responsible for delivery to the addre:t~ee, you are hereby notl)~ed that any review, dtssemina~'or~ discloaure, or copying of thi~ eommuntcation is ~trtctly prohibited. If you have received thi~ fac~inffle in error, please immediately notify us by telephone, and return the ortgmal facsimde to t~ at the address above vfa the U.S. Po~tal $*rvic~. ThaEkyou.