Tidal freshwater streams are key rearing habitats for juvenile salmonids in the Lower Columbia River. Large wood is an important part of salmonid habitat creating heterogeneity in the stream, providing shelter and quiet water, and providing a food source for fish. Wapato Valley Mitigation and Conservation Bank (Wapato Valley Bank) is located in Clark County, Washington, on 876 acres of diverse floodplain habitats in the Columbia River Estuary that have been altered over the last 170 years to meet human needs. Gee Creek serves as the southern property boundary of Wapato Valley Bank and flows for 2.35 miles from its confluence with the Columbia River at RM 87 to the eastern boundary of the site. Juvenile salmonids have been documented in Gee Creek using existing naturally recruited large wood, channel margins and oxbow habitats of this tidally influenced stream. Bank staff wanted to establish baseline large wood habitat data to compare post restoration conditions in Gee Creek. We sampled large wood habitat features in a 500-meter reach of stream starting at the creek confluence, including a 160-meter oxbow. The survey was modeled after the methods outlined in Schuett-Humes et al. 1999, and modified for a tidal freshwater location. Crews surveyed in September to take advantage of low water levels and measured single large wood pieces and log jams; size, and decomposition stage, orientation, associated deposition and scour features, and associated sediment storage within bankfull width.
Results/Conclusions
An average number of 28 pieces of large wood per 100 meters were found in lower Gee Creek. We expect to see slight changes in large wood composition year to year due to the tidal regime taking wood out of Gee Creek and piece recruitment upstream as trees fall in. As more floodplain forest becomes connected to Gee Creek with the removal of dikes and levees we would expect an increase in large wood habitat, especially after high water events. This survey will be replicated over time to monitor changes in large wood composition as restoration action changes the hydrologic regime on the Wapato Valley Bank site.