10-13-08 Drainage and Flooding Committee minutes

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k lot z 4~. ass 0 cia t e 5 required would be the design discharge divided by 150 cubic feet per second (rounded upward to the nearest whole culvert number). . Diversion ponds are off-line ponds potentially used when widening or lining, as discussed above, is 1) inadequate to lower water levels sufficiently to carry the design flow without bank-overflow, 2) considered unacceptable because of construction or environmental limitations; or 3) inadequate to prevent flooding in low-lying areas beyond the channel (low lying in comparison to the top-of- channel bank elevation) would require, for flooding of such areas not to occur (either directly or by backflow into sewer outfalls or bank cuts), that the water surface elevation for the design flow condition to be dropped to a very low level, so low that it could not be readily accomplished with widening or lining. A diversion pond, in essence, diverts some of the design flow out of the channel and temporally stores it so that tlle peak flow to be carried in tlle channel is lowered, and, a result, the maximum water surface is lowered. The procedure for determining the necessary storage volume to accomplish tlus is described in Section 3. It is more hydraulically-efficient that diversion ponds be located in the vicinity of areas where the flooding problems they are intended to remedy are located. Potential pond locations area discussed in regard to regional detention ponds discussed below; for effective diversion, ponds would be located in middle or downstream reaches of a channel at locations were open land were available. However, due to limited open land near the affected areas, some of the diversion ponds will have to be located in the upstream reaches of certain channels. 4-5 Klotz Associates Project No. 0127.008.000 January 2009 La Porte Citywide Drainage Study City of La Porte