Large-scale restoration of salmon spawning habitat in a regulated, gravel-bedded river
Abstract
Large-scale river restoration programs have recently emerged as a tool for improving salmon habitat in highly altered river ecosystems. Few studies have quantified the extent to which the restored habitat is utilized by salmonids, which physical processes contribute to improved biological functionality, or how the restored habitat changes over time. We investigated Pacific salmon spawning site utilization in two restored reaches of a gravel-bedded river: a site of gravel augmentation and habitat enhancement completed three years ago and a re-engineered, meandering channel and floodplain reach constructed over a decade ago. Spawning was observed at both sites in areas predicted to have high quality habitat, based on channel morphology and hydraulics. At the more recently restored gravel augmentation site, peak redd densities occurred in areas of high sediment mobility as determined by measurements of gravel pivot angles and a grain entrainment model. Redds were built in areas with high values of hydraulic conductivity and streambed hyporheic fluxes, which were located near the transition between pool-riffle bedforms in the re-engineered reach but spanned the entire length of the gravel-augmented reach. In situ measurements of streambed hydraulic conductivity indicated lower hyporheic fluxes at the re-engineered, meandering site due to the infiltration of fine sediment into the subsurface. Highly mobile and permeable gravels were heavily utilized for spawning in restored reaches amid an otherwise predominantly armored bed. However the potential long-term, ecological benefits provided by large-scale restoration projects will vary depending on the patterns of post-restoration flow, sediment supply and channel evolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP51B0909H
- Keywords:
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- 1813 Eco-hydrology;
- HYDROLOGYDE: 1820 Floodplain dynamics;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1879 Watershed;
- HYDROLOGY