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FS0001-CS001213Kimley-Horn and Associates, In¢, Suit~ 1800 12700 Park Central Drive Dallas, Texas 75251 December 13, 2000 VIA FACSIMILE 972.304.3673 HARD COPY VIA U.S. MAIL 4 pages total Mr. Ken Griffin, P.E. Director of Engineering and Public Works City of Coppell P.O. Box 478 Coppell, TX 75019 Re: CLOMR and CDC Application Review Estates of Denton Creek Coppell, Texas Dear Ken: Kimley-Horn and Associates, Inc. (KHA) has performed a review of the Estates of Denton Creek FEMA CLOMR Request for the 32.09 acre Holmes Tract, prepared by Nathan D. Maier Consulting Engineers, Inc. (IqDMCE), dated November 2000. A Corridor Development Certificate (CDC) application was also reviewed. The comments below address these items separately. The submitted report includes only data to apply for a Federal Emergency Management Agency (FEMA) Conditional Letter of Map Revision (CLOMR). The report does not include data related to the City's Floodplain Management Ordinance, such as addressing fully developed flows or valley storage requirements. KHA reviewed the document for adherence to FEMA criteria and have also noted instances where City criteria may not have been met with respect to the City Floodplain Management Ordinance or Subdivision Ordinance. KHA recommends that the following items be addressed by NDMCE. 1. The Effective and Annotated Flood Insurance Rate Maps (FIRM) showing the project impact to the FEMA floodplain/floodway are not readable in KHA's report copy. Please provide readable copies of these exhibits. · TEL 972 770 1300 FAX 972 239 3820 and Associates, Inc. City of Coppell, December 13, 2000, Page 2 2. On page one of the narrative report, it reads "The resultant water surface elevations due to the proposed grading of the Estates of Denton Creek...". This statement implies that there will be modifications to the floodplain elevations, while the remainder of the report maintains that the base flood elevations (BFE) for Elm Fork or Denton Creek will not change. Please provide clarification in the narrative. 3. The FEMA 100-year Floodplain reclamation proposed in this CLOMR could be accomplished using a CLOMR - F (CLOMR based on fill). Please explain the reasoning behind pursuing a CLOMR for this proposed reclamation. 4. The included FEMA MT-1 Form 3 outlines criteria for fill compaction and erosion control in the FEMA 100-year floodplain. It is suggested that this information be required on the grading plan for the site. 5. The Post-Project Conditions Work Map shows a portion of multiple lots will be located in the FEMA floodplain. It is suggested that the engineer be made aware of Subdivision Regulation Appendix C, Section II.5 a/b covering access to this floodplain area for maintenance and provide for this access via easements or other means. 6. The FEMA floodway should be shown on any workmaps showing the FEMA floodplain. 7. On FEMA MT-2 Form 1 Section 5, it states that the community will be responsible for performing maintenance on flood control structures associated with this project. The submitted CDC forms indicate that the owner will be responsible for maintenance. Clarification of this responsibility should be provided. 8. The HEC-2 model for Denton Creek and HEC-RAS model for the Elm Fork of the Trinity River are provided as supporting documentation to this report. The HEC-2 model includes existing condition geometry with fully developed condition flows. This model results in water surface elevations through the project reach that may inundate the site during a large storm event. This is evident comparing the resultant water surface elevations from the HEC-2 model to the grading shown on the Post- Project Conditions Work Map. It is also important to note that this model would not typically be included in a FEMA CLOMR submittal, rather the FEMA effective model for Denton Creek would be included. The narrative report states that the site falls within the ineffective flow area of the Sandy Lake Road Bridge over Elm Fork. For this reason, the narrative concludes that the effects of Denton Creek should not govern this floodplain. It is suggested that the engineer provide the FEMA and Associates, Inc. City of Coppell, December 13, 2000, Page 3 effective model for Denton Creek with any necessary geometry modifications (if proposed) and address the concem stated above regarding the fully developed floodplain. The FEMA effective model for Denton Creek will need to be evaluated to see if those water surface elevations pose a flooding hazard to the proposed development, or an alternate explanation provided. 9. Digital models have not been included with the CLOMR submittal. It would be helpful in review if these models could be provided. FEMA typically will request digital copies of the models used. 10. The Post-Project Conditions Work Map includes topographic contours to show the elevation of the site out of the 100-year FEMA floodplain. The narrative report states that the fill will be 2 feet above the BFE. At the northem end of the project, the BFE varies from 447.07 feet to 447.44 feet. The contours for the proposed fill in this area show 449 feet. Spot shots showing the proposed fill 2 feet or greater above the BFE should be shown on both the Work Map and reflected on the site grading plan. The CLOMR report is currently not complete for submittal to FEMA. The comments listed above should be addressed before a submittal is made. Additional comments to the ones listed above may be generated as a result of the reply to the above comments. The following comments pertain to the CDC application included with the submittal package. 1. A detailed Site Plan needs to be provided for adequate review of the CDC application. This site plan should include the items outlined on the application. 2. The hydrologic and hydraulic information included on Part 2 of the CDC form does not correspond to the FEMA regulatory information provided in the CLOMR report or the profiles and cross sections provided as attachments to the CDC application. Digital copies of the models should also be included. Please have the engineer provide the proper backup information for the forms. 3. Design and calculations for the valley storage mitigation swale should be included with the CDC applicationg. They currently are not included. A complete review of the CDC submittal could not be performed due to a lack of data. Please have the engineer provide a complete submittal for review. Additional comments to the ones listed above may be generated as a result of the reply to the above comments. and Associates, Inc. City or Coppell, December 13, 2000, Page 4 The City should evaluate the proposed development for impact to the fully developed floodplain and valley storage. The City should also coordinate the application for the CDC with the U.S. Army Corps of Engineers and be copied on transmittals from the engineer to the Corps, TNRCC, etc. to see that the City's requirements are met in this regard. With recent changes with the FEMA consultant reviewer, KHA would be pleased to provide the City of Coppell with details of the updated process. Let me know if you need this information. Please feel free to contact me if you have any questions or concerns, or need clarification of the comments. Sincerely, Kimley-Horn and Associates, Inc. Dan F. Grant, E.I.~v~' Project Manager G:~HYDRO\projects\63124004XCorresp~Let01Cty. doc CC: Lee Allison, KHA Frisco (via facsimile)