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4.3 <br />From TSARP models flow at Spencer Bridge is 2,730 cfs and increases to 3,264 cfs, an <br />increase of 437 cfs, between Bandridge Road and the confluence with B 112-02-00 due to <br />full development contributing runoff to the channel. Downstream of the confluence with <br />B 112-02-00 flow increases to 3,429 cfs, an increase of 165 cfs. Within the reach between <br />Spencer Highway and B112-02-00, Willow Springs Gully is at bank full conditions, <br />causing flooding in Brookglen for the 100-year even. <br />Channel velocities from north of Spencer Road to just north of Bandridge bridge are <br />approximately 5.9 fps and consistent from one cross section to the next within the reach <br />which indicates the channel is at normal depth. The cross section north of the confluence <br />indicates an increase in the velocity to 8.5 fps associated with the increase of 437 cfs in <br />flows for a total flow of 3,264 cfs. The cross section remains unchanged until this area. <br />Differences between the energy grade and water surface in this reach ranges between <br />0.52 ft and 1.12 ft. <br />Downstream of the confluence additional flow within the concrete channel section <br />increases to 3,429 cfs in the larger cross sectional area of the 20-foot wide low flow <br />section with a velocity of 6.5 fps. Just down stream velocities drop between 3.7 fps and <br />4.4 fps with additional increases in flow within the grass lined channel section. <br />Differences between the energy grade and water surface in the grass lined section average <br />0.25 ft and 0.66 ft in the concrete section down stream of the confluence. <br />Confluence of B112-00-00 with B112-02-00 <br />Flow upstream and downstream of the confluence is close to normal depth or about 12.5- <br />feet for the 100-year event. The normal depth discharge in B 112-00-00 upstream and <br />downstream of the confluence is similar for the same normal depth of 12.5-feet. With <br />this logic, flows were calculated for 4-feet to measure the effects of the confluence <br />configuration on tributary B112-02-00 using empirical formulas. The 4-foot depth was <br />4-2 <br />Klotz Associates Project No, 0127.009.000 Fairmont Park East & Brookglen Drainage Study <br />May 2009 City of La Porte <br />