07-09-18 Drainage and Flooding Committee Meeting

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REQUEST FOR DRAINAGE COMMITEE AGENDA ITEM Agenda Date Requested: July 9, 2018 Requested By: Lorenzo Wingate Department: Public Works ("* Report Ir" Resolution" Ordinance Exhibits: Appropriation Source of Funds: Account Number: Amount Budgeted: Amount Requested: Budgeted Item:" Yes" No SUMMARY & RECOMMENDATION The B112-02-00 channel segment of Willow Springs Bayou is a concrete lined trapezoidal channel that flows from east to west, where it merges with the B112-00-00 Channel (Willow Springs Bayou). Flooding in the Brookglen subdivision is due to backwater from B112-00-00 backing up into B112-02-00, per the 2009 Fairmont Park East & Brookglen Drainage Study, prepared by Klotz Associates. The B112-02-00 has about 200-acres of contributing drainage area and the channel is approximately 2,500 feet in length between B112-00-00 and Canada Rd. Willow Springs Bayou is a concrete line trapezoidal channel with a 4' deep low flow section. Upstream of the confluence, the low flow section is 12' wide with 16' benches and concrete riprap side slopes from Deer Park, upstream of Spencer Hwy., to the confluence with B112- 02-00, or 1,200-feet upstream. Downstream of the confluence the low flow section expands to 20' wide with 14' benches and concrete riprap side slopes between B112-02-00 and about 920' downstream where the channel transitions to an earthen trapezoidal section with a 30' bottom width and 4H:1 V side slopes. The Willow Springs Bayou continues south of Fairmont Pkwy, into Pasadena and ultimately converges into Armand Bayou. A drainage study, prepared by Klotz Associates in May 2009, concluded that reductions in the water surface elevation within B112-02-00 can be achieved by reducing the backwater effects of B112-00-00 and by addressing flows coming into the City from upstream. In August 2009, Klotz Associates prepared a hydrologic and hydraulic analysis to evaluate HCFCD Unit B112-02-00 and determined the benefits of redirecting the B112-02-00 channel to drain east to Unit B109-03-00. There were two options modeled, with "Option 1" resulting in a maximum water surface reduction in B112-00-00 of -0.60 ft and an average of -0.23 ft, and a maximum flow reduction of -301 cfs. Maximum water surface reduction in B109-00-00 was -0.36 ft and occurs in B109-03-00. Average water surface reductions along B112-02-00 are -0.89 ft between B112-00-00 and Canada Street. "Option 2" provides an average water surface reduction in B112-00-00 of -0.44 ft and average flow reduction of -269 cfs. Average water surface reduction in B109-00-00 is estimated at -0.13 ft and average flow increase around 65 cfs. Average water surface reductions in B112-02-00 are -1.09 ft between B112- 00-00 and Canada Street with associated reduction in flow of 182 cfs.