Coarse sediment delivery and routing in the White River

Science Center Objects

The Issue: Ongoing channel aggradation has reduced flow conveyance along the lower White River, increasing the flood risk in urban-suburban areas. A refined understanding of the delivery, transport and deposition of sediment in the White River, and how those processes may be influenced by climate and existing dam operations, is necessary in order to plan for future flood hazard in the lower White River.

How USGS will help: This study will build upon previous efforts by quantifying the current and potential future rates of sediment production, transport, and deposition in the lower White River to better inform capital flood-risk reduction and environmental restoration projects along the Lower White River in King County.

White River at Mud Mountain Dam

White River at Mud Mountain Dam

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

Problem: Ongoing channel aggradation has reduced flow conveyance along the lower White River, increasing the flood risk in urban-suburban areas of the cities of Auburn, Pacific and Sumner. Channel aggradation has been a persistent problem in the lower White River, related to the naturally high sediment yields from headwaters on Mt. Rainier, but forecasted climate change has the potential to accelerate aggradation as a result of changes in regional hydroclimatology and sediment supply dynamics. A refined understanding of the delivery, transport and deposition of sediment in the White River, and how those processes may be influenced by climate and existing dam operations, is necessary in order to plan for future flood hazard in the lower White River.

Objectives: The objective of the study is to quantify current and potential future sediment supply and depositional trends in the White River to better inform capital flood-risk reduction and environmental restoration projects along the Lower White River in King County.

Relevance and Benefits: This study will provide information on the timing and magnitude of sediment production rates and mechanisms that drive these rates in the steep, pro-glacial environments on the flanks of a stratovolcano, and the morphologic change associated with those sediment transport processes which affect flow conveyance and flood hazards. This information will help inform our understanding of how upstream sediment inputs translate into downstream geomorphic response, notably vertical adjustment in the bed of the White River, and improve our understanding of the likely trajectory of downstream channel change under a changing climate. This information will directly inform projects related to flood hazards and capitol improvement.

Approach: This project takes a combined approach that includes 1) analysis of repeated topographic (lidar) surveys, 2) analysis of repeated aerial photographic surveys, 3) synthesis of existing information, and 4) a specific USGS stream gage analysis.