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Session C7 - Regenerative design applications to sustain baseflow to enhance fish passage in urban channels
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Abstract
Fish passage restoration has historically focused heavily on creating hydraulic conditions within a channel or fishway that are favorable for upstream migration with respect to the physiology of the target fishes. This approach has proven successful for the upstream migration of adult fishes on larger rivers, but does not always translate well to the second and third order streams where the impacts of urbanization are most pronounced. In urban environments the stream hydrology and chemistry has been significantly altered to a point where miles of stream no longer support perennial flow year round. Consequently, upstream migrations can be successful, yet the young of the year and resident fish populations are stressed due to the lack of adequate baseflow. Even the most elegant fish passage or restoration project could be considered a failure if upstream rearing habitats are not sustainable. This presentation discusses two regenerative design applications to restore watershed hydrology and moderate the stream hydrograph such that the baseflows in urban channels a sustained year round and resident fish passage and rearing habitats are enhanced. The first case study is an in-channel approach that maximizes in channel pool habitat and forces frequent overbank flows to restore the water table in the upper watershed. By storing water in the upper watershed, baseflows in the lower watershed are sustained as the water seeps to the channel through shallow subsurface and hyporheic pathways. Delivering water to the lower watershed through these pathways also influences the stream temperature such that coldwater fisheries can also be enhanced. The second case study is a project aimed to mitigate the impacts of a planned development that threatened to rob the hydrology and increase water temperature in a regionally unique native trout stream. A regenerative approach to upland stormwater management was applied to mimic the sites natural hydrology and convert surface runoff to shallow subsurface flows that reduced peak flows and elongated the falling limb of the hydrograph such that baseflow and water temperatures were sustained. These applications have the ability to 1) directly restore fish passage by increasing the depth of baseflow in the channel and over obstructions and 2) enhance the success of traditional fish passage projects by creating sustainable in-stream habitats in urban channels.
Type
article
event
event
Date
2012-06-07