Klotz Draft Report for Fairmont Park East and Brookglen 072809

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Mr. Ron Bottoms July 22, 2009 Page 4 of 12 Study Background Interconnect B109-03-00: Original purpose of the interconnect B 109-03 -00 was to divert flood waters along B 112- 02-00 to the improved downstream channel B109-00-00 and reduce flooding in Brookglen Subdivision and Spencer Highway Estates Subdivision during a 100-year storm event. According to a report entitled, Hydrologic and Hydraulic Study for Interconnect of HCFC Unit B112-02-00 to Unit B109-00-00 and HCFC Regional Detention Site Unit B512-01-00, by WSA in April 1997; HCFCD constructed an interconnect, now called B109-03-00, between Tributary 1.78 to Willow Springs Bayou (B 112-02-00) and Spring Gully (upper B 109-00-00) as an interim solution to "reduce widespread flooding" along B 112-00-00 and B 112-02-00. Prior to construction of interconnect B109-03-00, B112-02-00 drained all of subwatershed B11202A, an area approximately 1,612 acres located in the City of Deer Park, eastern limits and north of City of La Porte. The limits of B109-03-00 are between B112-02-00 and approximately 700 feet to the south of B112-02-00 and just south of Carlow Street to the east approximately 900 feet to B109-00-00. Construction of the interconnect B109-03-00 was completed in November 1993 in accordance to plans prepared by J.A. Costanza & Associated Engineering, Inc., dated February 1992, see "Data Collected and Prior Reports". The disconnect of B 112-02-00 at Canada Street was performed to divert all flows coming from B512 01 00 into B 109-00-00 under the ultimate development plan in order to have no impacts to Armand Bwith the interconnect in place and 1997 develo meat. HCFCD Detention Basin B512-01-00: originally, an interim plan recommended by WSA in 1997, proposed detention basin B512-01-00 serve to provide: (1) Downstream flood protection along B112-02-00 and B 112-00-00, "primarily" in Brookglen Subdivision and Spencer Highway Estates Subdivision, (2) Mitigate impacts along Armand Bayou (B 100-00-00) from constructing the interconnect B109-03-00; (3) Provide detention required from constructing East Boulevard Roadway. According to WSA's 1997 report, the interim plan provided flood protection along B 112-02-00 for a 10- to 25-year storm event level between Spencer Highway and the interconnect. The interconnect split the 100-year flows from B512-01- 00 on the order of 75% (about 760 cfs) of the flow was added to B109-00-00, (and 75% removed from discharging into B 112-00-00) and 25% (about 254 cfs) continued downstream in B112-02-00. Interim mitigation plan provided 351 ac-ft that outfalls using 2-7' x 6' RCB's under an 80-foot spillway discharging 1015 cfs into B112-02-00 at a depth of 9.5-feet.