Fine sediment infiltration in Chinook spawning gravels in the Sauk River Basin, Washington

Science Center Objects

The Issue: There is concern that inherently high finer-grained (small gravel, sand, and silt) sediment loads in the Sauk River system may adversely affect egg-to-fry survival of ESA-listed Chinook salmon in the Sauk River and lower Skagit River Basin. However, there are no quantitative data for the Sauk River basin to assess if fine sediment deposition and infiltration into spawning gravels are at levels that could adversely affect egg-to-fry survival. 

How USGS will help: The objective of this study is to quantify fine sediment deposition and intrusion in spawning gravels of Chinook salmon in the Sauk River during the incubation and pre-emergence period and determine if fine sediment intrusion of salmon redds can be predicted by other more easily measured factors including the quality of spawning gravels or substrate on nearby exposed bars, or turbidity. The results from this study can be used to inform fish population models as part of ongoing species recovery efforts.

Sauk River

Sauk River

(Credit: Scott Anderson, USGS. Public domain.)

Problem: There is concern that inherently high finer-grained (small gravel, sand, and silt) sediment loads in the Sauk River system may adversely affect egg-to-fry survival of ESA-listed Chinook salmon in the Sauk River and lower Skagit River Basin. However, there are no quantitative data for the Sauk River basin to assess if fine sediment deposition and infiltration into spawning gravels are at levels that could adversely affect egg-to-fry survival. 

Objectives: The primary objective of this study is to quantify fine sediment deposition and intrusion in spawning gravels of Chinook salmon in the Sauk River during the incubation and pre-emergence period. The secondary objective is to determine if fine sediment intrusion of salmon redds can be predicted by other more easily measured factors including the quality of spawning gravels or substrate on nearby exposed bars, or turbidity. The geographic scope of the proposed study includes upper, middle, and lower reaches of the mainstem Sauk River immediately upstream of its confluence with the White Chuck River and the confluence of the Skagit River.

Relevance and Benefits: The study is consistent with the USGS strategic science directions “A National hazards, risk, and resilience assessment program” and “Understanding Ecosystems and Predicting Ecosystem Change” identified in the 2007-17 science strategy of the USGS (Evenson and others, 2013). The results from this study can be used to inform fish population models as part of ongoing species recovery efforts.

Approach: The proposed project will be accomplished in four tasks over a four-year period. Intrusion of fine sediment into Chinook salmon redds will be quantified using Whitlock-Vibert® boxes in artificial redds (Task 1). Grain size distributions of sediments in Chinook spawning habitat where there is not active spawning and nearby dry gravel bars will be conducted through grain size analyses of bulk sediment sampling (Task 2). Turbidity will be monitored at an existing USGS streamgage station in the lower Sauk River, and the Sauk-Suiattle Indian Tribe will provide a furnished record of turbidity for the Suiattle River (Task 3). Finally, grain size distributions of spawning areas and nearby gravel bars, and turbidity will be evaluated to determine if these variables can serve as predictors or indicators of the potential for fine sediment intrusion into spawning redds (Task 4).