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Item 6A - Flooding LetterMe6 100 TO: FROM: DATE: Tons M. Matthews, Jr. • 1600 E Southluke Blvd. . Suite 110-.313 Southluke, Terns 76091 MEMO KEN BAKER TOM MATTHEWS FAX NO.: 817/481-4074 TELE NO.: Of. - 817/329-6996 Mo. 214/676-3434 EMAIL: tmatthews@fourpeaksdev.com MARCH 30, 2009 SUBJECT: GLOSSER ADDITION Ken, per your request from our meeting last week, please find enclosed a letter and backup material from Michael Boyd, RE with Nathan D. Maier noting that a development like we are proposing will actually be better for the flooding issue. Please call me if you should have any thoughts, questions or comments Thanks, tan SID NATHAN D. MAIER ple CONSULTING ENGINEERS, INC. %,A KR 3 0 INS lpjan61nc March 27, 2009 Tom Matthews, Jr., Principal Four Peaks Development, Inc. 2600 E. Southlake Blvd. Suite 120-323 Southlake, Texas 76092 RE: Proposed Glosser Addition, Southlake, Texas Dear Mr. Matthews: I have provided a preliminary look at the potential project that we discussed yesterday. The project involved platting four 1-acre residential lots out of a larger 10-acre tract that is bounded by North Peytonville Avenue and Sleepy Hollow. Higgins Branch flows south to north through this parcel, which will separate the easterly 4 single-family lots from the westerly larger property. AS we discussed, I ran a preliminary hydrology model on Higgins Branch watershed to establish the impact of adding some impervious area to the Sleepy Hollow property (adding 4 lots to this tract). Pre project (existing conditions) have a peak combined flow of 3038 cfs with 98 cfs coming off of the design subarea. For post project (with the proposed development) we have a peak combined flow of 3030 cfs with 132 cfs coming off the design subarea. We are increasing the flow off of our area by 34 cfs but decreasing the peak flow in the creek by 8 cfs, The condition is created because the runoff response time is faster when we put streets in to convey the runoff from the smaller area but the larger watershed response time remains unchanged, When the storm hydrographs are combined we get a slightly decreased peak discharge at our point in the watershed. Attached are copies of the computer models and a copy of the watershed map. If you have any questions concerning this analysis please call or email. Thanks, 44 Michael Boyd, A.E. Executive Vice President Two Park Lane Place / 8080 Park Lane / Suite 600 / Dallas. Texas 75231 / (214) 759-4741 r CL, rf ~ f~ s 1 r f u {{f fl 4 f Y 1 ~-fr''3r .~~I r • ~ e F~ rr F f ~j 1 i... 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