Chehalis Watershed Suspended Sediment Monitoring
The Issue: The Chehalis River deposits sediment in Grays Harbor, which the U.S. Army Corps of Engineers regularly dredges to maintain shipping access. The sources and overall volumes of sediment transport in the lower river were last assessed in the 1960s. Given substantial changes in land-use and watershed regulations over the subsequent half-century, there is an open question as to if or how sediment loads in the river have changed.
How USGS will help: The USGS will conduct suspended sediment monitoring at three locations in the Chehalis Watershed, providing updated information on the spatial patterns and overall volumes of sediment delivery to Grays Harbor. Monitoring will be conducted over several years using a combination of continuous turbidity, which has been shown to be a good proxy for suspended sediment, and discrete suspended sediment samples collected during high flows. These data will allow for an updated assessment of typical sediment delivery to Grays Harbor.
Problem: Sediment delivery to Grays Harbor has not been directly monitored since the 1960s, leaving the contemporary rate of sediment loading uncertain.
Objectives: The goal of this work is to provide updated estimates of sediment delivery to Grays Harbor.
Relevance and Benefits: This work will provide updated information on sediment delivery used to plan and conduct dredging operations in Grays Harbor. This work will also expand regional understanding of contemporary sediment loads and how those loads have changed relative to mid-20th century conditions.
Approach: Suspended sediment loads will be estimated using a combination of continuous turbidity and discrete suspended sediment concentration (SSC) samples. SSC samples will be used to develop SSC-turbidity relations, allowing continuous predictions of SSC over the period of turbidity monitoring. Monitoring will occur on the Wynoochee River, Satsop River, and the Chehalis River near Porter, accounting for roughly 85 percent of the total drainage area of the Chehalis River at Grays Harbor.
The Issue: The Chehalis River deposits sediment in Grays Harbor, which the U.S. Army Corps of Engineers regularly dredges to maintain shipping access. The sources and overall volumes of sediment transport in the lower river were last assessed in the 1960s. Given substantial changes in land-use and watershed regulations over the subsequent half-century, there is an open question as to if or how sediment loads in the river have changed.
How USGS will help: The USGS will conduct suspended sediment monitoring at three locations in the Chehalis Watershed, providing updated information on the spatial patterns and overall volumes of sediment delivery to Grays Harbor. Monitoring will be conducted over several years using a combination of continuous turbidity, which has been shown to be a good proxy for suspended sediment, and discrete suspended sediment samples collected during high flows. These data will allow for an updated assessment of typical sediment delivery to Grays Harbor.
Problem: Sediment delivery to Grays Harbor has not been directly monitored since the 1960s, leaving the contemporary rate of sediment loading uncertain.
Objectives: The goal of this work is to provide updated estimates of sediment delivery to Grays Harbor.
Relevance and Benefits: This work will provide updated information on sediment delivery used to plan and conduct dredging operations in Grays Harbor. This work will also expand regional understanding of contemporary sediment loads and how those loads have changed relative to mid-20th century conditions.
Approach: Suspended sediment loads will be estimated using a combination of continuous turbidity and discrete suspended sediment concentration (SSC) samples. SSC samples will be used to develop SSC-turbidity relations, allowing continuous predictions of SSC over the period of turbidity monitoring. Monitoring will occur on the Wynoochee River, Satsop River, and the Chehalis River near Porter, accounting for roughly 85 percent of the total drainage area of the Chehalis River at Grays Harbor.