Drainage and Flooding Report January 2009

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k I o t z I 1kr4 I associates • Lining of channel bottom and side slopes to increase channel conveyance by reducing frictional losses: Lining, while sometimes necessary as the only viable option, is not a preferred technique because of costs and environmental impacts. • Channel berming at low points: Berming of a channel to form, in effect, a local levee at locals where the top of bank elevation is low can be used to help contain high flood waters, but in fact may not function as intended in an urban environment because of crossings beneath the berm by sewer pipe. • Widening of a channel: Widening a channel to improvement its capacity is a preferred feasible technique provided adequate right-of-way is available so that adjacent properties are not adversely impacted. • Improvement of hydraulic structure capacity: Bridges, to some extent, and culverts, often to a considerable amount, can significantly reduce the capacity of a channel. If data are available for estimating the impact of hydraulic structures on channel capacity, improving structure capacity, or at least significantly reducing the constrictions that hydraulic structures like culverts introduce, can be considered. 2.4.5 Detention Detention is used for several primary purposes in drainage and flood control: • On -site Mitigation of Runoff: On -site detention for mitigation of increased runoff due to development of an area. • Diversion of Channel Flow: Off-line detention for diversion purposes to reduce existing channel flows by diverting flow to the diversion pond and reducing flow and stages in the channel from which the diversion occurs. • Off -site Mitigation of Runoff: Off-line regional detention for mitigation due to increased runoff from several sites simultaneously. 2-12 Klotz Associates Project No. 0127.008.000 La Porte Citywide Drainage Study January 2009 City of La Porte