Laserfiche WebLink
<br />selected because the transition between upstream and downstream occurs in the low flow <br />section. Increases in discharge from upstream to downstream of the confluence were <br />calculated for a depth of 4-feet to be about 255 (cfs) upstream and 329 (cfs) downstream <br />or a difference of 74 (cfs). For the same depth in tributary B1l2-02-00 normal depth <br />flow is calculated to be 1,038 (cfs), which is much larger due to its larger cross sectional <br />area. Since no increases in water surface for Bl12-00-00 are observed, contributing flow <br />from tributary B 112-02-00 will be small compared to flow at normal depth and greater <br />depths at the confluence. This indicates that the depth at the confluence controls flow in <br />B 112-02-00 due to backwater conditions. <br /> <br />4.4 Conclusions & Recommendations <br /> <br />Reductions in water surface at the confluence can be achieved by reducing the backwater <br />influence of Bl12-00-00. One way to do this is to increase the cross sectional area of the <br />channel downstream by removing the benches in the channel and eliminating the 20-foot <br />low flow section. In addition to removing the benches or increasing conveyance, <br />detention will have to be considered. Locations for possible detention include an <br />undeveloped area just upstream of Fairmont Parkway on the west bank of B1l2-00-00, <br />undeveloped area just downstream of Fairmont Parkway on the east bank of B 112-00-00 <br />or possible areas north of Spencer Highway to name a few examples. <br /> <br />Construction estimates for removing the 890-foot bench section are approximately $1.10 <br />million with a lO% contingency. Detention basin unit costs are typically in the range of <br />$8,000-$12,000 per acre-foot of detention. The buyout locations adjacent to Bl12-02-00 <br />total approximately 2.20 acres. For a depth in the channel of lO-feet, approximately 22.0 <br />ac-ft of storage is available from these locations at an average cost of $220,000. <br /> <br />It is concluded that reductions in the water surface elevation within B 112-02-00 can be <br />achieved by reducing the backwater effects of Bl12-00-00 and/or by addressing the high <br /> <br />4-3 <br /> <br />Klotz Associates Project No. 0127.009.000 <br />May 2009 <br /> <br />Fairmont Park East & Brookglen Drainage Study <br />City of La Porte <br />