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Denton Creek/Sandy Lake-CS071016 I~ Kimley-Horn and Associates, Inc. October 16, 2007 . Suil 127 Dal 752 Mr. Kenneth M. Griffin, P.E. Director of Engineering/Public Works 255 Parkway Boulevard Coppell, TX 75019 RE: Conditional Letter of Map Revision based on Fill (CLOMR-F) and Corridor Development Certificate (CDC) Permit Application Review Sandy Lake Tracts 1- V KHA No.: 063124008 Dear Mr. Griffin: Kimley-Hom and Associates, Inc. (KHA) has performed the first review of the Denton Creek CLOMR-F application and CDC Permit application for Sandy Lake Tracts I-V, dated August 27,2007, prepared by Nathan D. Maier Consulting Engineers, Inc. (NDMCE). KHA reviewed the document for adherence to currently published City of Coppell Floodplain Management Ordinance, Federal Emergency Management Agency (FEMA) guidelines, and the third edition of the CDC manual. KHA recommends that NDMCE address the following items: General 1. The effective model shows the subject tracts are within an ineffective flow area of the Elm Fork of the Trinity. However, the subjecUracts are also adjacent to Denton Creek and within the floodplain of Denton Creek. The City- Wide Storm water Management Study for the City of Cappel! shows that Denton Creek conveys approximately 23,000 cfs in ultimate conditions. Provide existing and proposed hydraulic models for .1 r-r1 1 1 1. 1 :~ Kimley-Horn and Associates, Inc. Mr. Kenneth M. Griffin October 16, 2007 Page 2 of 4 2. The CDC application shows grading will occur within the FEMA regulatory floodway. Section 60.3(d) ofthe National Flood Insurance Program regulations requires a detailed hydrologic and hydraulic analysis to show that proposed development will not result in an increase in base flood elevation within the community. Development includes any man-made change, including excavation. 3. The Floodplain W orkmaps should state the vertical datum used for the on-ground survey. 4. The reports and exhibits include references to Denton Creek, Elm Fork of the Trinity, and East Fork of the Trinity. These items should be revised to be consistent. 5. The CDC Permit application workmap shows fill on Tracts II, III, and IV. The CLOMR-F application workmap shows fill on Tracts III and IV. The CLOMR-F application forms shows fill on Tracts III, IV, and V. Revise these items to be consistent with each other or explain the discrepancy. 6. The CDC Permit application shows fill to be placed to an elevation of 446 and the CLOMR-F application shows fill to be placed to an elevation of 445. Revise the forms and workmaps to be consistent with each other or explain the discrepancy. 7. The floodplain workmaps for both submittals should show detailed proposed grading. This should include all proposed cut and fill. 8. The creek flowline and name should be clearly labeled on the floodplain workmaps. 9. The 445 contour should be shown in its entirety on the floodplain workmaps. 10. A note should be included on the plat which lists the minimum finished ..... ..... . ~ ~...... .. . :~ Kimley-Horn and Associates, Inc. Mr. Kenneth M. Griffin October 16, 2007 Page 3 of 4 CLOMR-F 1. The metes and bounds description of the property to be removed from the floodplain includes all or portions of Tracts I-V. Each tract should be included on FEMA form MT-l Form 2. 2. The floodplain workmap should show the boundary from the metes and bounds description. Survey elevation points within the boundary should be included to confirm the lowest lot elevation locations. 3. The workmap shows that the Base Flood Elevation for Tract III and IV is 444.7 based on cross section 939+40. The delineation reflects a Base Flood Elevation greater than 445 on the eastern portion of the tracts. Revise FEMA form MT-l Form 2 to reflect the correct Base Flood Elevation. 4. The lowest lot elevation on Tracts I-IV within the area shown to be outside the floodplain is lower than the 444.7 elevation shown on MT-l Form 2. The floodplain workmap should be revised to clarify that areas lower than 444.7 are not in the floodplain due to a lower floodplain elevation. 5. The existing and proposed floodplain delineations remove areas outside of the metes and bounds from the FEMA effective floodplain. A Letter of Map Revision submittal will be required to formally revise the FEMA effective floodplain boundary to what is shown on the workmap. CDC 1. Provide detailed valley storage computations for pre-project and post- project conditions. 2. The floodplain workmap should show the existing 100-year floodplain delineation. I~ Kimley-Horn and Associates, Inc. Mr. Kenneth M. Griffin October 16, 2007 Page 4 of 4 If you have any questions regarding the comments included in this letter, please feel free to contact us at 972.770.1300. Sincerely, KIMLEY-HORN AND ASSOCIATES, INC. cS~/~? ~fL Steven D. Galloway, P.E., CFM Brad W. Pickering, EIT, CFM cc: Michael Boyd, P.E.; Nathan D. Maier Consulting Engineers, Inc.