Initial effects of habitat restoration using large wood: linking stream geomorphic change and fish response in the Oregon Coast Range
Abstract
Restoration efforts to improve stream habitat for salmonids often include the addition of large wood (LW), yet the success of these efforts over time in streams of different size and geomorphic settings remains poorly understood. In addition, success is rarely directly measured in biological terms due to the difficulty of collecting fish data at the appropriate temporal and spatial scales. Given the high cost of restoration it is important to understand the effects of restoration efforts in different settings to better allocate limited resources. Here we present the results of a large restoration effort conducted in 2015-2016 in a 34 km2 coastal watershed in Oregon where 680 LW pieces were added to the stream channel to improve fish habitat. Coho Salmon smolt production and adult returns have been monitored in this watershed since 1997, making it an ideal location to investigate the biological return on investment for a LW placement project. To evaluate geomorphic response, we combined hydraulic modeling in three sites (5-12 km2), annual topographic surveys up to 4 years after LW placement and detailed topographic surveys before and after the restoration in 7 additional sites (3-22 km2). Surveys and hydraulic modeling indicated a 30% decrease in velocity after the LW additions, as well as improved flood plain connectivity, increases in channel width and the creation of secondary channels. However, these changes are channel size dependent; larger sites responded more quickly to LW addition, but changes in smaller sites may be more enduring due to relatively lower wood mobility. Results from the first 2 years of fish monitoring following the LW addition showed a 29% increase in Coho Salmon smolt abundance compared to the 10-year pre-treatment average. Smolt abundance at nearby control sites showed a much smaller increase over the same time frame. Increased overwinter survival rates for juvenile Coho Salmon following LW addition indicated that improved winter habitat conditions were driving increased smolt production. Overall, the fish response has been commensurate with observed changes in channel form and results from hydraulic modeling. Additional data collection over the next 4 years will help us further evaluate relationships between ongoing geomorphic change and Coho Salmon smolt production in Mill Creek.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP34B..05S
- Keywords:
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- 0483 Riparian systems;
- BIOGEOSCIENCESDE: 0483 Riparian systems;
- BIOGEOSCIENCESDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1820 Floodplain dynamics;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGYDE: 4217 Coastal processes;
- OCEANOGRAPHY: GENERALDE: 4217 Coastal processes;
- OCEANOGRAPHY: GENERAL