Chinook Bend-Tolt Large Wood Debris (LWD) Assessment

Summary

Wild Fish Conservancy will work with an environmental engineering firm to assess the feasibility of large wood (LWD) supplementation in the Snoqualmie River from its confluence with the Tolt River, downstream to Harris Creek near Chinook Bend Natural Area (River Mile 21-25). The assessment will lay the foundation for conceptual designs that will detail instream LWD treatments in the Chinook Bend -Tolt reach of the Snoqualmie River. This project will conduct public outreach to assess recreational boater usage in a 4-mile reach of the Snoqualmie River that is critical salmon habitat. We will then use the information gained from the public outreach to inform the design of conceptual Large Woody Debris (LWD) habitat restoration treatments in the reach.

#1 Ranked project in the WRIA 7 Salmon Recovery Funding Board in 2021.

Location
Start Date
Mainstem of the Snoqualmie River, from the confluence with the Tolt River to the confluence with Harris Creek (WRIA 7)
09/01/2021
Project Type
Completion Date
Watershed Assessment
09/01/2023

Goals & Objectives

The primary deliverable for this project will be conceptual designs for LWD placement in the project reach. We anticipate creating conceptual designs for at least three treatment sites within the greater project reach, these designs will be informed by the assessment of recreational boating in the reach. Additional deliverables will include stakeholder outreach meeting notes and minutes and public feedback received regarding recreational boating and habitat restoration in the project reach.

Recent assessments of instream LWD as a function of adjacent riparian forests in the Pacific Northwest (Martens et al 2020) have shown that without mature riparian forests, many river reaches will not reach historic LWD loading without several hundred years time or LWD supplementation. The Chinook Bend -Tolt reach of the Snoqualmie River is an important reach for both spawning and rearing for Chinook salmon. For this reason the reach has been targeted for floodplain reconnection and restoration projects. Despite these efforts, LWD loading in the reach is low relative to historic levels.  Design considerations for the reach include boater safety, maximizing complex edge habitat in the reach, and structural stability in a large river environment.

Instream large woody debris (LWD) derived from riparian forests was a key structural element in large river floodplain channels. Old growth forests contributed massive pieces of wood to adjacent stream channels, often hundreds of feet long with large complex crowns and basal diameters in excess of 10 feet. These logs played a key structural role in regulating the formation of complex floodplain habitat by providing floodplain roughness elements, which force alluvial sediment storage and scour at the valley bottom scale, directing channel pattern. These logs also played an important role at a more localized scale. Instream LWD that is in contact with the river channel during low-flow river conditions provides complex rearing habitat for juvenile salmon. Large log jams are also often associated with deep pools, providing cover for adult salmon that are staging in a given reach before spawning.

This project addresses inadequate LWD loading and instream habitat conditions in the floodplain reaches of the Snoqualmie River from the Tolt River confluence to the Harris Creek confluence in the Stillwater Wildlife Unit. This area includes some of the most productive spawning reaches in the Snoqualmie River, where known Chinook spawning occurs annually. Numerous large-scale floodplain restoration projects have occurred in this reach over the last decade, however, post project monitoring shows that wood loading in the system is still < 5% of the median level and <1% for key pieces, when compared to similar sized reference rivers in Washington State.

Benefits of Wood in the River at reach scale:

  • LWD as channel roughness
  • Velocity vectors and flow routing
  • sediment deposition and erosion
  • Riparian forest development
  • Channel pattern
  • Complex fish habitat
Primary Habitats Impacted By Project:
Managing Agency/ Organization:
Mainstem and Floodplain
Wild Fish Conservancy
Project Contact:
Budget or Project Cost:
Micah Wait
$151,758
Funding Sources:
Partners:
Salmon Recovery Funding Board and King County Flood Control District (FCD) Cooperative Watershed Management (CWM) Grant Program
Natural Systems Design

Attachment(s)