Willamette Instream Flows

Background

The USGS is exploring how rearing habitat for spring-run Chinook salmon and winter steelhead trout varies with the amount of water in the Willamette River. There are more than a dozen dams on the tributaries to the Willamette River which largely determine streamflows in the mainstem Willamette River throughout the year. These dams were primarily built to reduce the risk of flooding throughout the Willamette Valley, though other authorized purposes include hydropower generation, recreation, and water supply for agricultural and municipal users. However, these dams also have a detrimental effect on the native spring Chinook and winter steelhead fish populations which are listed as Threatened under the Endangered Species Act. Seasonal streamflow targets have been established on the mainstem Willamette River and its major tributaries to support different life stages of these fish. This research will help determine if existing streamflow targets meet the biological objectives or if the targets need to be refined. 

Objectives

The USGS is developing detailed two-dimensional models to simulate the water depths, velocities, and inundated areas for a variety of flows along the Willamette River from Eugene to Newberg. Fish biologists from partner agencies will utilize these results to assess how the availability of rearing habitat changes in response to changes in flow which can inform flow management decisions.

In order to develop these models, we must accurately map the shape and elevation of the river and surrounding areas. Starting in 2017, the floodplain topography and shallow areas were mapped by Quantum Geospatial using topographic-bathymetric lidar. In 2018, the USGS surveyed deeper areas of the river and will be merging these boat-based surveys with the lidar data to create a seamless map of the shape of the river and its floodplain.

Anticipated products and timelines

• Willamette River bathymetry data (collected via boat-based sonar) – Summer 2018
• Digital Elevation Model combining 2017 topo-bathymetric lidar with sonar bathymetry data – Fall 2018
• Two-dimensional models of Willamette River from Eugene to Newberg – Spring 2019
• Summary report describing model development and findings - Summer 2019