Study results available! Snoqualmie River Three Forks to Falls Geomorphic Report

Hello Friend of the Upper Snoqualmie River,

The King County Flood Control District, together with King County as service provider, led a study to better understand the causes and effects of erosion noticed in the Upper Snoqualmie River, between Snoqualmie Falls and the Three Forks area where the Middle, North, and South Fork Snoqualmie rivers combine. 

The study was designed to understand impacts to the Snoqualmie River from changes made to Snoqualmie Falls from 2004 to 2012. Changes to the Falls widened the Snoqualmie River channel and lowered the weir at Snoqualmie Falls, resulting in increased river flow over the Falls. Together, these actions decreased local flooding upstream of the Falls. 

Erosion is a natural river process, but it can be impacted by human actions. The study confirmed the Upper Snoqualmie River’s banks and channel have eroded since changes at Snoqualmie Falls. It is unclear how much erosion is due to those changes. Other possible causes of erosion in the Upper Snoqualmie River may include natural changes in the channel and river flow, sediment trapping in the Three Forks area, and adjustments due to changed land use and forestry practices.     

The King County Flood Control District, together with King County as service provider, will continue collecting data to monitor erosion and deposition of the Upper Snoqualmie River’s channel. King County will also continue to inspect the conditions of river protection structures on a regular basis.   

Contact Andy Gendaszek, (206) 477-8296 or agendaszek@kingcounty.gov, for more information.

Access the report or learn more in the Snoqualmie-Skykomish River Watershed webpage (under projects and studies)!