Klotz Draft Report for Fairmont Park East and Brookglen 072809

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Mr. Ron Bottoms July 22, 2009 Page l❑f12 watershed should be conducted to determine actual changes. A summary of the changes is located at the end of this section. Option 1 The first option includes all the following items and shown in Exhibit 4: 1) Interconnect Spring Gully (HCFCD Unit B 109-03-00) and Tributary 1.78 to Willow Springs Bayou (HCFCD Unit B 112-02-00). This includes connecting the east end of B112-02-00 to B109-03-00 and local channel improvements. 2) Disconnect Willow Springs Bayou (HCFCD Unit B 112-00-00) and Tributary 1.78 to Willow Springs Bayou (HCFCD Unit B 112-02-00). This means damming off the west end, or disconnecting, B112-02-00 from B112-00-00 (Willow Springs Bayou). 3) Add a low flow drain pipe at the disconnect to drain B 112-02-00. Install a low flow pipe at the proposed disconnect to drain B 112-02-00 into B 112-00-00 during periods of no rain or when B109-03-00 empties. No channel improvements are proposed for B112-02-00 nor is the existing flow line modified. 4) Add a bridge or Five (5) 11'x 10' reinforced concrete boxes (KCB's) along with local channel improvements at B112-02-00 and Canada Street. 5) Spring Gully (B109-03-00 & B109-00-00) Channel Improvements between the proposed interconnect of B 112-02-00 and B 109-03-00 to approximately 4,800- feet south to Future HCFCD Detention Basin B509-03-00 51.0 ac-ft of channel excavation). Typical section is a trapezoidal shape about 14-feet deep with bottom widths that vary from 20-feet to 35-feet and 4:1 side slopes. 5) Interim detention in Future HCFCD Detention Basin Unit B509-03-00 of approximately 92 ac-ft with a stabilized earthen inflow weir and outfall pipe. Mitigation of the increases in flow from B 112-02-00 and additional conveyance in B109-00-00 will be handled by constructing a portion of detention basin B509- 03-00 with temporary inflow and outfall structure. Option 2 The second option includes all the following and shown in Exhibit 5: 1) Propose 56.4 ac-ft for detention along B112-00-00, B 112-02-00 and B 109-03-00 to reduce the amount of detention required in HCFCD basin B509-03-00 and minimize needed channel improvements in B 109-00-00 to convey flow. a. Location D1 —14.8 ac-ft of storage is available for detention along B112- 02-00 from 1.9 acre buyout location along Gladwyne Court. This requires purchase of two (2) single family houses, demolition of the structures and excavation on Gladwyne Court.