New USGS Study Tracks Millions of Tons of Rocks, Gravel and Silt Carried by the Sauk River
TACOMA, Wash. — The U.S. Geological Survey recently published the results of a new five-year suspended-sediment and water temperature study from the Sauk River. The purpose of this study is to improve understanding of the magnitude and timing of suspended sediment from the Sauk River and its tributaries to the Skagit River.
The Sauk River is a federally designated Wild and Scenic River that drains a relatively undisturbed landscape along the western slope of the North Cascade Mountain Range, Washington, which includes the glaciated volcano, Glacier Peak. Naturally high sediment loads characteristic of basins draining volcanoes like Glacier Peak make the Sauk River a dominant contributor of sediment to the main stem Skagit River downstream.
“The Sauk River is a great place to begin these detailed investigations around western Washington because it is unaffected by levees, dams, dredging or development in general,” said Kristin Jaeger, a USGS research hydrologist and lead author of the report. “We found that sediment from the eastern flank of Glacier Peak may contribute about 50 percent of the sediment load for the entire Sauk River Basin in any given year.”
The study was conducted over a five-year time span and collected detailed information from three stream gages on suspended sediment carried by the river. Suspended-sediment loads on the Sauk are highly variable from year to year and appear to largely be driven by the occurrence of atmospheric rivers and other fall and early winter precipitation events. Sediment load is also influenced by basin conditions that vary from year-to- year and can be elevated if more sediment is available for transport by rivers from recent debris flows or landslides.
Additionally, the Sauk River serves as important spawning and rearing habitat for several salmonid species in the greater Skagit River system. Because of the importance of sediment to morphology, flow-conveyance and ecosystem condition, there is interest in understanding the magnitude and timing of suspended sediment and turbidity from the Sauk River system and its principal tributaries, the White Chuck and Suiattle Rivers, to the Skagit River.
The study also monitored stream water temperature at the three stream gages. Maximum summertime water temperatures rarely exceeded levels that could cause stress for salmon during the five-year study. However, summertime water temperatures were higher in years of smaller snowpack. With precipitation forecast to occur increasingly as rain instead of snow, water temperatures may also increase.
The report, “Suspended Sediment, Turbidity, and Stream Water Temperature in the Sauk River Basin, Western Washington, Water Years 2012–16” is published and available online.