Snoqualmie Large Wood Placement Concept Design

Wild Fish Conservancy worked with Natural System Designs to develop a conceptual basis of design for a LWD restoration project in the Greater Tolt Alluvial Fan reach of the Snoqualmie River (RM 21-25). The Snoqualmie River throughout the reach was evaluated through a field visit, which occurred on August 3rd, 2022, and a series of desktop analyses to determine the recommended treatment types for the conceptual design. Treatments under consideration for this design should address the severe lack of large wood within the project reach, enhance in-stream channel complexity, and reconnect the Snoqualmie River to its historical floodplain, particularly in locations where restoration opportunity is the greatest and current development and infrastructure would not be put at risk. An alternatives analysis was conducted in order to evaluate the three potential restoration sites and select a preferred alternative. Each project was qualitatively assessed in terms of the potential habitat benefits and the risk to recreational users and infrastructure. Each project was given a score of 1-3 for each category and the scores were used as a basis to select a preferred alternative. Through the alternatives analysis process, the Stillwater Project Area was selected as the preferred alternative because it provides the greatest habitat benefits and lowest risks to recreational users and infrastructure. A project within the Stillwater Wildlife Area also has support from local stakeholders including WDFW and King County.

A conceptual design vision was developed for the Stillwater Project area as part of this project. The vision involves establishing an area where levels of large wood reach reference levels and there is enough space for the river to create and sustain a variety of habitat types. A restoration corridor would be established where dynamic river processes are encouraged within the project area and infrastructure can be protected outside of it. This design anticipates the imminent avulsion and uses large wood placements in order to maintain a multi-thread channel pathway in both the current main channel and within the oxbow network. This will be accomplished by placing a high density of large wood within the existing main channel to encourage a flow split. Wood will also be strategically placed within the oxbow network, likely at a lower density, so that multiple channels can be maintained and the floodplain channels do not fill with sediment and become abandoned. An existing rock revetment will be removed so that a preferred flow path can be developed naturally. The design can be adapted if the avulsion occurs before restoration is implemented. The details of the design will be refined during future phases of the project. 

The project goals and objectives remained the same.