The U.S. Army Corps of Engineers Portland District last week released a final environmental impact statement for its Willamette Valley System that was six years in the making.
Publication of the 88-page final EIS is the first step in a two-step approach to continue operations and comply with the Water Resources Development Act of 2024 (WRDA 2024), which requires USACE to analyze an alternative that ceases hydropower operations at the eight dams in the WVS that generate electricity.
Section 1326 of the new law prevents the Corps from completing its overall review of operations and maintenance of the system and consultation with federal agencies, until we prepare and formally analyze an alternative that ends federal hydropower operations in the Willamette Valley. Thus, it will need to create a supplement the EIS just completed. The Corps says it expects to complete that supplemental EIS in the spring of 2026 and decide how to operate and maintain the WVS for 2026 and beyond.
The second step will be a supplemental EIS to include this new analysis and the effects of a deeper drawdown of Detroit reservoir as required by the 2024 National Marine Fisheries’ Biological Opinion, released last December, which concluded that dams in the Willamette Valley are driving salmon to extinction.
“The completion of this EIS is a significant milestone that deserves celebration, but there is more to do,” said Col. Dale Caswell, Jr., Portland District commander. “Over the next year, we will have another opportunity to listen to the public and work with our partners to finalize how we will operate these dams for future generations.”
The Corps manages the Willamette Valley System of dams, which stores and releases water from 13 reservoirs within the Willamette River Basin to meet congressionally authorized purposes such as flood control, fish and wildlife, hydropower, recreation, irrigation, water supply, water quality, and navigation.
The primary purpose of the system, flood risk management necessitates keeping reservoir elevations low to maintain storage space, capture rainfall and minimize flooding potential through spring. This must be balanced with what seem to be conflicting purposes: refilling the reservoirs before summer for irrigation, hydropower generation, water quality improvement and recreation.
The last EIS by the Corps for the Willamette Valley System was completed in 1980. Since then, operations have been changed and structures built to improve conditions for fish species listed under the Endangered Species Act. “Considerable information has become available since the 1980 EIS was completed, which has been incorporated into the existing conditions and analyses in the current FEIS,” it states.
The current EIS analyzes the environmental and social benefits and impacts of seven action alternatives and a No-action Alternative. The alternatives are distinguished by operational or structural measures, designed to improve flow, water quality, and fish passage.
The preferred alternative in the document, to continue operations and maintenance of the Willamette Valley System for specific, authorized purposes under legislation passed by Congress, would improve fish passage throughout the WVS, manage water quality downstream of WVS dams using a combination of modified operations and structural improvements, and to balance water management flexibility to meet downstream water requirements for fish and wildlife.
Local impacts would include construction of a small temperature management structure in the adult fish ladder at Foster Dam and operations to manage downstream temperatures below Green Peter Dam, as well as gravel augmentation measures downstream from Foster.
The FEIS states that results from its preferred alternative will likely include:
- Cultural resources would be negatively impacted during drawdowns (due to exposed archeological sites) at Green Peter;
- Conservation water storage at Green Peter would reach its capacity less than 75% of years during the spring and would reach the bottom of conservation storage about 5% of years during deeper drawdowns in late fall;
- Debris removal would negatively impact geology and soils at Green Peter;
- Wetlands at Green Peter would be adversely affected due to landslides induced by the fall and spring drawdowns;
- Water quality below Foster would be “substantially more adverse,” as would turbidity below the dam;
- Harmful algae blooms would be “moderately adverse” at Foster; and
- Effects of mercury would be “moderately more adverse” at Foster.
Learn more at the USACE Willamette Valley System EIS webpage.