Channel Modification (also called Conveyance Improvements)
Channel modification is a man-made change to a channel's characteristics, typically for the purposes of reducing flood damages by increasing its overall conveyance capacity. This can be accomplished by widening and/or deepening the channel, reducing the friction by removing woody vegetation, or by occasionally adding concrete lining. It should be noted that only 6% of the channels in the county's drainage infrastructure inventory are concrete lined.
Widening of Sims Bayou
Stormwater Detention (Basin)
A stormwater detention basin is another structural tool used by the District when implementing a project. A stormwater detention basin is a large, usually excavated area of land, frequently adjacent to a channel, which is designed to receive and hold above-normal stormwater volumes. The detained stormwater then slowly drains over time out of the detention basin as water surface elevations in the receiving channel recede.
Rendering of Keith-Wiess Park showing flooding conditions and normal conditions.
Bypass Channel Construction
Bypass channel construction could also be a man-made change to a channel's characteristics. However, rather than necessarily increasing a channel's capacity, a bypass channel diverts excess stormwater "around" an area with restricted right-of-way or an area with sensitive environmental values. Specifically, bypass channel construction involves building a new channel that is attached to an existing channel and, as mentioned, conveying the excess stormwater runoff around its original path. Bypass channels usually "short circuit" the meander or curve of a bayou and are usually constructed in conjunction with downstream channel modifications or a detention basin.
Jersey Village Bypass Channel, 2010.
Bridge modification is another structural tool used in flood damage reduction. It involves the replacement, extension or modification of a bridge in order to remove an impediment to flow within a channel and/or accommodate channel modifications. It can also lessen the likelihood of debris snagging on the bridge piers. If done in conjunction with channel modification, a bridge modification is typically completed first.
Law Street Pedestrian Bridge
A levee is a physical barrier constructed to protect areas from rising floodwaters. Levees are not feasible in most cases in Harris County for a variety of important reasons. Levees typically remove valuable flood plain storage and block the ability of the channel to move water. There are also concerns with rainfall that falls within the levee itself. Most importantly is the possibility for catastrophic and sudden failure under extreme flood events, potentially resulting in loss of life and total destruction of property.