06-11-18 Drainage and Flooding Committee Meeting

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REQUEST FOR DRAINAGE COMMITTEE AGENDA ITEM Agenda Date Requested: June 11, 2018 Requested Ru• I nren7n \A/innata/n Pannall Department: p- --"li^ %Nnrks Report: Resolution: Ordinance: Exhibits: Budset 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. The City of La Porte is working closely with the City of Pasadena in the review of the pending Pasadena Convention Center Drainage & Detention Evaluation. RPS was recently retained by the City of Pasadena to perform a drainage and detention evaluation study for the ultimate development of the 198-acre Pasadena Convention Center (PCC site) along B112-00-00 (Willow Springs Bayou) between W. Fairmont Parkway and Red Bluff Road. There are two underlying objectives of this study: 1) provide recommendations for drainage improvements to the City of Pasadena in order to mitigate the adverse impact resulting from PCC development and 2) determine the benefit of adding 100 ac-ft of volume to the basin, 200 ac-ft of total volume, for the City of La Porte to decrease the risk of flooding along Willow Springs Bayou between Spencer Hwy and W. Fairmont Parkway. As indicated in the City of La Porte's 2009 Citywide Drainage Study, mitigation of increased runoff due to drainage improvements within the City may be required to prevent adverse impacts upon downstream locations, beyond the City's boundaries. That being said, contingent upon the potential upstream benefits of the proposed additional 100 ac-ft of volume along Willow Springs Bayou, recommendations presented within the 2009 Citywide Drainage Study and the 2009 Fairmont Park East & Brookglen Drainage Study will need to be re-evaluated.