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SECTION 4 <br />BROOKGLEN SUBDIVISION <br />CONFLUENCE OF HCFCD UNIT B112-00-00 & UNIT B112-02-00 <br />4.1 Background <br />Flooding in Brookglen Subdivision is due to the effects of backwater in Willow Springs <br />Gully (B 112-00-00) backing up into tributary B 112-02-00. HCFCD Unit B 112-02-00 is <br />a concrete lined trapezoidal channel that flows from east to west where it intersects with <br />B112-00-00, (See Exhibit 6). B112-02-00 has about 200-acres of contributing drainage <br />area and the channel serving the area is approximately 2,500-feet in length between <br />B112-00-00 and Canada Road. The City requested Klotz Associates analyze the local <br />hydraulic conditions at the confluence of HCFCD Unit B112-02-00 and Willow Springs <br />Gully (B 112-00-00) for improvements alternatives to reduce water surface elevations in <br />tributary B112-02-00 upstream of the confluence. <br />Willow Springs Gully is a concrete lined channel with a 4-foot deep low -flow section. <br />Upstream of the confluence, the low flow section is 12-feet wide with 16-foot benches <br />and concrete riprap side slopes from Deer Park upstream of Spencer Highway to the <br />confluence with B112-02-00, or 1,200-feet upstream. Downstream of the confluence the <br />low flow section opens up to 20-feet wide with 14-foot benches and concrete riprap side <br />slopes between B 112-02-00 and about 920-feet downstream where the channel transitions <br />to an earthen trapezoidal section with 30-foot bottom width and 4H:1V side slopes. <br />4.2 Existing Model <br />To verify backwater conditions, results from the existing RAS model were compared for <br />cross sections through Brookglen subdivision. B112-00-00 reaches bank full conditions <br />for the 100-year even before flow reaches the northern City limits at Spencer Highway. <br />4-1 <br />Klotz Associates Project No. 0127.009.000 Fairmont Park East & Brookglen Drainage Study <br />May 2009 City of La Porte <br />