Engineers in northern Idaho are designing a unique upstream fish passage facility for the Albeni Falls Dam on the Pend Oreille River.
Built in 1955, the dam that is 90 feet tall blocked the access of the native migratory fish species to their natural cold-water spawning grounds.
This project will incorporate the use of a fish lock mechanism operated together with special transport trucks.
The double-pass approach targets connecting threatened bull trout to 750 miles of upstream habitat.
Blocking a historic migratory corridor in 1955
Albeni Falls Dam is 1,080 feet in length and crosses the Pend Oreille River at Oldtown, Idaho.
Although this dam plays a key role in flood prevention and produces forty-two megawatts of hydroelectric energy, the physical barrier made it impossible for the indigenous aquatic organisms to migrate.
Migratory bull trout rely on river flow to migrate between deep lakes, where they feed and spawn in the upper river reaches.
Thus, by cutting off this route, downstream populations of bull trout were separated from Lake Pend Oreille for about 70 years.
Fish ladder design was not considered effective because of drastic changes in lake level and complicated hydraulics of local rivers.
To move the fish over 90 feet of concrete structures, engineers have proposed an unconventional mechanical method. The U.S. Army Corps of Engineers is planning a special fish trap for bull trout.
Trapping fish inside a pressurized attraction lock
This design of the passage uses a unique entrance channel made directly in the tailrace located beneath the dam’s spillway.
Engineers plan to channel water current to the entrance so as to guide the bull trout upstream into a submerged chamber.
This attraction current is like those found in rivers, which migrating fish instinctively follow when looking for upstream paths.
After getting the fish into the collection chamber, engineers will use mechanical gates to block their access to the lower part of the chamber.
The water gets into the vertical lock chamber to increase its internal water levels equal to the upper reservoir.
Mechanical crowding screens will help in moving the fish into the sorting facility.
Transporting migratory trout in custom climate-controlled trucks
Releases above the spillway could cause the disoriented fish to be washed downstream back through the power turbine or spillway gates.
To reduce turbine mortality to zero, biologists plan to stock-capture bull trout using special haul vehicles.
These special transportation vehicles will incorporate specially designed tanks with controlled temperature and oxygen flow rates to ensure minimal physiological stress.
Each captured fish is then checked, measured, and tagged with microchips.
The haul vehicle will then transport the fish around the perimeter of the dam and release them at predetermined locations on the lakeshore.
Reconnecting hundreds of miles of cold tributary habitat
Reestablishing passage will open up access to an extensive system of pure cold-water streams within the upper watershed.
Over 750 miles of historical habitat exist above Albeni Falls Dam within the Pend Oreille basin.
Bull trout need cold, clear water that is below 50 degrees Fahrenheit to breed and raise their young.
The threats of climate change and fragmented habitat have increased the importance of higher altitude and colder water refuge areas.
Re-establishing disconnected sections of the river allows for natural genetic flow between once separate trout populations.
Balancing hydroelectric generation with native species recovery
The planned Albeni Falls project demonstrates how legacy water infrastructure can adapt to modern ecological restoration requirements.
Integrating fish transport operations will allow the dam to maintain flood control protection and regional hydroelectric generation.
Federal agencies and regional tribes worked together closely in developing the trap-and-haul system specifications and protocols, according to the Seattle District, U.S. Army Corps of Engineers – Northwestern Division.
Telemetry monitoring using continuous radio will be used to trace released fish for long-term spawning success evaluation in the basin.
Successful implementation may become a model for future fish passage projects at high-head dams in the Pacific Northwest. Investment in mechanical fish passage ensures both the production of clean energy and repair of interconnected river ecosystems.
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