1890s Side Channel Restoration Effectiveness Monitoring

Side channel restoration to improve juvenile salmonid rearing habitat remains a key component of the Upper Columbia Basin salmon recovery habitat enhancement strategy. The goal of this project was to evaluate benefits and limitations of connecting side channel systems using groundwater infiltration galleries. The project evaluated how the 1890s side channel was used by coho, steelhead, chinook, and bull trout. It also explored the potential impact the thermally enhanced flow has on growth and survival of juvenile salmonids. Metrics of juvenile growth and survival collected from 1890s Side Channel were compared to similar data collected by co-managing agencies that are monitoring other recently completed side channel restoration actions including: Silver side channel (another groundwater fed channel), 3R side channel (a flow through channel) and Whitefish Island side channel (another flow through channel).

Snorkel surveys and spawning ground surveys were used to document fish use of 1890s side channel by season, species, and life stage. Fish growth and survival rates were measured through remote PIT tagging and subsequent recapture and detection. Statistical comparisons were made between the results obtained from the 1890’s channel and results obtained from other side channel and main-stem habitats in the Methow Basin collected through ongoing monitoring efforts conducted by co-managing agencies (WDFW for Silver side channel and BOR for 3R and Whitefish Island).

We learned a great deal of information about the 1890s side channel through implementation of the 1890s Side Channel Monitoring Project despite being unable to confirm some of our hypotheses. We demonstrated that the 1890s side channel was used year-round by target species. Juvenile coho were typically the most abundant species and life history stage present at a given time. Both coho and steelhead used the channel as spawning habitat. Chinook did not spawn in the channel. Out-migrating smolts used the channel for brief periods in the spring. Juveniles of all three target species entered the channel throughout the year and many overwintered. Density and abundance of juvenile salmonids typically increased from summer to fall and fall to winter.

Our analysis of size and growth data provided mixed results. While significant differences between side channels were observed in age-1 coho and age-0 steelhead, patterns were not always clear or consistent. However, analysis did demonstrate that juvenile salmonids in the 1890s had late-winter fork lengths either significantly larger than fish in the flow through mainstem side channels or lengths that were not significantly different. Juvenile salmonids in 1890s side channel were as large as the fish observed in Silver side channel. It is highly likely that there were multiple variables influencing growth that could not be measured by a project of this size. We suspect that differences in sampling methodologies, juvenile salmonid density, and forage availability would also need to be included in analyses comparing side channels with differing flow sources.

Our overwinter survival estimates did not produce statistically significant results. The difference in mean overwinter survival rates appeared to favor the 1890s side channel but the inter annual variation is likely too large to allow significant results from such a limited study. It is still possible that with further research a biologically significant improvement in juvenile salmonid overwinter survival could be observed. This will be particularly true if the impacts of climate change exacerbate the existing negative influence of water temperature on juvenile salmonid survival in the Middle Methow Reach and cold-water refugees, like 1890s side channel, become increasingly important.

A full description of the methodology, results, and discussions, including tables and figures, can be found in the final progress repor

This project sought to evaluate benefits and limitations of using groundwater to restore side channel habitat. The project detailed how target and non-target species use the restored 1890s side channel and demonstrated that the habitat is used extensively by juvenile salmonids. The evaluations of the effectiveness of this type of side channel restoration action towards increasing juvenile growth and survival in relation to other side channel reconnections provided mixed but generally positive results. Thermal refuge habitat may become increasingly important as the impact of climate change continues to threaten salmon and steelhead in the upper Columbia. Observed fish use and evidence suggesting a potential positive influence on growth and survival may encourage co-managing agencies to explore the use of groundwater infiltration galleries to create thermally enhanced surface flow that would provide refuge against warming surface waters.