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FS9904-CS 990902 '- ~ ~=~ Kimley-Horn and Associates, Inc. September 2, 1999 Mr. Kenneth M. Griffin, P.E. Director of Engineering and Public Works City of Cop pel I 255 Parkway Blvd Coppell, Texas 75019 Re: Response to review of the Schreiber Tract CLOMR for Denton Creek, City of Coppell, Texas Dear Mr. Griffin: The following are responses to comments received by Halff Associates regarding the Schreiber Tract CLOMR along Denton Creek. These comments are attached for your reference. In addition to addressing these comments, the original submittal dated March 1999 has been revised to incorporate changes made to the effective models used as the basis for this study. The change to the effective models were made as part of a Letter of Map Revision request prepared by Dunaway Associates for the Mansions on the Lake multi-family development located opposite the Schreiber Tract on Denton Creek. The LOMR for this project was approved on July 8, 1999. The submittal by Kimley-Horn in March of 1999 was based on models approved as part of the CLOMR for Mansions on the Lake. After a discussion with Michael Baker Corporation and Dunaway Associates, we were informed that these models were revised based on as-built conditions at Mansions on the Lake. Michael Baker Corporation also revised the effective models immediately upstream of our project (at the S.H. 121 bridge) in order to "tie" into other models. The changes to these models were incorporated into our study and had a minimal effect on the previous results. The revised CLOMR reflects usage of the new effective models. . TEL 972 770 1300 FAX 972 239 3820 H :\HYD ROlprojectsl06309 3061CO RRESPlresp2 .doc . Suite 1800 12700 Park Central Drive Dallas, Texas 75251 . '. ~=~ r- r- Kimley-Horn and Associates, Inc. In addition to the revision ofthe effective models, some of the cross-sections were revised north of Denton Creek to better reflect the aerial topography. The following are responses to review comments received from Halff Associates: I. City of Coppell Flood Plain Management Ordinance A. The effective models used in our study are from a recently approved LOMR for the Mansions on the Lake multi-family development directly opposite the Shreiber Tract on Denton Creek. These models do not include the bridge at SH 121. I spoke with Laura Bittner at Michael Baker Corporation about these models. She said the bridge at SH 121 has not been included because it does not impact the I OO-year floodplain. It is labeled on the stream profiles in the Flood Insurance Study as a high bridge. During the review phase of the LOMR for Mansions on the Lake, Michael Baker Corporation made revisions to the model at SH 121 and upstream of SH 121. These revisions included adding ET cards beginning at Section 39290 to model ineffective flow at SH 121 and modifying upstream sections to better tie into another model. Since these revisions were made recently (June 1999), no changes were made to the effective models outside of the Schreiber tract limits. B. The channel at SH 121 is lined with gabion baskets and gab ion mattresses. C. The loss in "storage" shown at the upstream end of the computer model is a result of lower water surface elevations (less volume of water), not an actual loss in storage due to fill. D. Wetland issues will be addressed during site development. E. The ponds for Mansions on the Lake are constructed and have been labeled as existing ponds. Also, the extent of the excavation is now shown on the basemap. F. All issues related to the Flood Plain Development Permit Application will be addressed during site development. H :\HYDRO\projects\06309 306\CORRESP\resp2 .doc '- ~=~ Kimley-Horn and Associates, Inc. II. FEMA A. Form 6, Channelization, has been included in the report. B. The flood profile exhibit has been revised to include the 10, 50, 100, and 500-year profiles, as well as cross section labeling and community name. The 500-year floodplain limits will be added if requested by FEMA. C. The channel at SH 121 is armored with gab ion baskets and mattresses. D. The channel Manning's n-value was revised to reflect the Manning's n-values used in the effective models. E. Sections 394+40 and 394+90 have been added to the basemap. Section 394+40 will not be affected by the proposed cut or fill. If you have any question regarding any of the above, please do not hesitate to call. Sincerely, KIMLEY-HORN AND ASSOCIATES, INC. f1i;i/~.j, ILU-.. if)tiJuM 7( ~ William G. Pembroke, P.E. Vice President Michelle R. Evans, E.I.T. Project Manager MRE/fas H :IHYD ROlprojectsl06309 3061CO RRES Plresp2 .doc