Federal water managers will begin spilling hundreds of thousands of gallons of water over spillways instead of through turbines during annual “spring spill” operations at U.S. Army Corps of Engineers’ dams on the lower Snake and Columbia rivers.
The operations, which primarily benefit juvenile fish, start April 3 on the lower Snake River and April 10 on the lower Columbia River. These actions are intended to decrease the time it takes juvenile salmon and steelhead to move through the system of dams to the Pacific Ocean as well as provide a non-turbine passage route past the dams.
“For the past several years, we have worked with our regional partners to operate the dams in a manner that is as beneficial as possible for fish including out-migrating juvenile salmonids, returning adult salmon, steelhead and lamprey as well as resident fish” said Tim Dykstra, USACE’s Northwestern Division Fish Policy lead. “It’s always challenging as we seek to balance regional needs regarding dam operations including flood risk management, hydropower production, navigation and fish management objectives,” Dykstra said. “Very high volumes of spill that benefit juvenile fish can sometimes disorient and hamper adult fish migrating upstream.”
Spring spill has occurred since the mid-1990s to improve conditions for juvenile fish and USACE has adjusted spill as biologists have studied what worked. Spill levels vary at each of the eight dams, but all projects have an upper limit that protects water quality such as total dissolved gas (TDG).
Even though this additional water is valuable for fish passage, managers must reduce spill amounts to keep from exceeding 125% TDG limits that state water quality agencies set and EPA approved in Washington, which adds more intricacy to water management in the basin.
USACE will use specific operations at Lower Monumental, Little Goose and Lower Granite dams to balance both juvenile downstream and adult upstream passage by adjusting spill once adult fish arrive. Water managers will reduce spill for up to eight hours each day to allow adult salmon to find fish ladders and migrate upstream to spawn. Adults successfully migrated upstream during eight hours per day of performance standard spill in previous years. Performance standard spill is the spill level federal agencies have determined meets fish passage targets. Agencies call the daily fluctuating operation “flexible spill.”
Various federal agencies and plaintiffs agreed to the following spill operations to benefit fish passage:
- Bonneville, McNary and Ice Harbor dams will spill up to the 125% TDG levels 24 hours per day.
- The Dalles Dam will spill 40% of the river over the spillway (equivalent to 2022 spill levels).
- John Day Dam will spill 16 hours per day up to the 125% TDG levels and reduce spill for up to eight hours to performance standard spill levels or 32% of the river.
- Little Goose will also spill 16 hours per day up to the 125% TDG levels and reduce spill for eight hours to performance standard spill levels, or 30% of the river. This is to benefit adult fish passage.
- Lower Granite and Lower Monumental dams will begin spilling up to the 125% TDG levels for 24 hours per day, until adult fish counts reach a certain trigger level. Once the adult counts meet the triggers, but no later than April 24; then spill eight hours of performance standard spill: Lower Granite Dam 20,000 cubic feet per second and Lower Monumental Dam 40% of the river, and 16 hours of spill up to 125% TDG.
The Columbia River Basin is a large and complex system with variable stream flows and weather patterns. The economic vitality of the region and its tribes, communities, industries, and fish and wildlife species all depend on the system’s ability to provide for multiple uses, including flood risk management, hydropower, navigation, irrigation, recreation, water quality, and fish and wildlife.
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Originally published at https://www.nwd.usace.army.mil/Media/News-Releases/Article/3346277/water-managers-begin-spring-spill-to-benefit-juvenile-salmon/