Longevity of Large Wood Restoration Success to Improve Coho Salmon Habitat: A 2D Modeling Approach
Abstract
Coho salmon abundances in Coastal Oregon watersheds have significantly declined since predevelopment conditions primarily due to the creation of undesirable stream characteristics for juvenile fishes during high flow conditions. Large wood (LW) additions have been a heavily practiced restoration mechanism used to improve native fish habitats. However, we lack information regarding LW's long-term benefits. We used a field calibrated hydraulic model, Nays2DH, to evaluate hydraulic conditions relevant to acceptable fish habitat 2 to 6 years post LW restoration in three alluvial fish-bearing tributaries of the Siletz River in Coastal Oregon, USA. Acceptable salmon habitat was assumed when flow velocity was slower than the critical swim speed of the juvenile Coho fish (vcrit = 0.5 m/s) and stream bed refuge was stable represented by the likelihood of entrainment of the median size sediment particles in the stream bed. We observed that the maintenance of the initial benefits of the restoration effort estimated in an increase in the acceptable fish habitat of around 30% appears to depend on the original orientation of the LW pieces and the size of the stream relative to the size of the logs below the bankful flow. Preliminary modeling results indicate that as a result of increased floodplain connectivity from the LW introductions, reductions in water velocity primarily occur near the banks of each reach and maintained or increased velocity occurs near the thalweg. Downstream log jams also appeared to experience the largest amount of change, relative to the upstream log jams in each reach. Maintenance of acceptable coho salmon habitat 7 years after the LW introductions indicates that LW has the potential to continually improve or maintain created fish habitat over numerous years, specific to the reach scale characteristics. The findings from this research are ecologically important for identifying locations of restoration for species that require longer time frames of maintained acceptable habitat for population recovery or for land managers that strive to improve sustained instream hydraulic complexity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMEP52C0778M