What Have We Learned Five Years After Large Wood Placement Project on the South Fork Tolt River: A Meaningful Approach to Monitoring

Large Woody Debris in Pacific Northwest rivers create and maintain habitat processes by storing gravel, promoting lateral sediment and riparian wood recruitment and instream structure and complexity. In the South Fork Tolt River, a high energy gravel-bedded river in western Washington, an upstream dam has altered flow and bedload movement, and logging has removed instream wood and decreased large woody debris recruitment potential. Following two in-depth studies of river habitat and conditions, large wood placement was considered the most effective action to increase gravel for salmonid spawning, activate historic channels for juvenile rearing, and augment older decaying jams.  Based on a detailed geomorphic analysis and design, we installed engineered log jams (ELJs) at two sites and strategically placed “key member” logs in ten other sites by helicopter. The project was tested two years later by flows matching highest flows on record and exceeding the ELJs design flows. We monitored project success using photo points, longitudinal profiles, cross sections, facies mapping, low elevation aerial photography and Chinook salmon spawning surveys.  After five years:

• Most wood stayed in the system though movement and shifting did occur. Some wood that moved was trapped in other jams and our placed jams trapped other wood.
• Chinook salmon spawning distribution increased substantially in newly accessed channel.
• Channel access occurred at both small and large scales.