Tests of a new turbine at Ice Harbor Dam show the new fixed-blade design is 4 percent more efficient than the prior version and improves survival rates of juvenile salmon that migrate downstream past the turbine, officials say.
"The direct survival results and efficiency improvements of this unit exceed expectations and open the door for further testing and potential rebalancing of operations at the project, improving total project survival and maximizing the stewardship of this precious resource in the Pacific Northwest," Shawn Nelson, the U.S. Army Corps of Engineers' hydraulics and hydrology branch chief, said in a news release.
Two more turbines at Ice Harbor will be replaced by similar turbines over the next three years, and plans are underway to replace all 14 turbines at McNary Dam.
The 4 percent increase in efficiency means the Ice Harbor Dam could generate enough extra electricity to power 3,000 more households, Corps spokesman Joseph Saxon told NW Fishletter in an email.
Initial tests using balloon-tagged juvenile Chinook and artificially intelligent "sensor fish" indicate that passage through the new turbine rivals that of spillway passage, which is thought to be the safest in-river route for juveniles migrating past the dam.
The Corps used the two approaches to test juvenile survival last fall, after the new turbine was in place and began operating.
The agency tested survival of 1,424 balloon-tagged juvenile Chinook passing through the turbine, which resulted in a direct survival rate across the turbine unit's operating range of 98.25 percent. A 2007 study at Ice Harbor Dam using the same method calculated direct survival through the prior turbine style at about 96 percent, Saxon said.
The Corps also tested the turbine with 720 sensor fish, designed by researchers at Pacific Northwest National Laboratory to mimic what happens to fish as they pass through turbulent water and turbines.
"Significant reductions in strike, exposure to shear, turbulence and low-pressure zones, coupled with the high direct survival numbers put the turbine passage route at the same level or better than spillway passage," USACE hydraulics engineer and project technical lead Martin Ahmann said in the Corps' news story.
For the test on live Chinook, Saxon said, balloons are attached to the dorsal region of the fish and filled with a chemical mixture that reacts with water.
"We inject water into the balloons, then release the fish into the turbine," he continued. "After a couple of minutes, the fish have passed through the turbine, and the chemical reaction inflates the balloons. A boat crew recaptures the fish that have buoyed up to the surface, inspects them for physical injury and holds them in a recirculating pool for 48 hours to estimate survival."
The tests were done for three different operating points in the turbine unit's operating range, since pressure and turbulence that impact fish can be affected by environmental factors such as volume of water in the river or volume passing through the turbine.
Tests using the sensor fish were conducted by a team of PNNL researchers, according to an article written by the national laboratory. "The team released them at three different elevations so that we could collect data to understand passage close to the tip, middle, and hub of the turbine's blade," Daniel Deng, a laboratory fellow at PNNL, said in the article.
Each sensor provides researchers with roughly 2,000 measurements per second of pressure, acceleration, rotational velocity and orientation. Deng said his team conducted a similar test in 2015 with the previous turbine, and preliminary results show the new turbine provides better hydraulic conditions for fish.
Saxon said no other species have yet been tested. Juvenile Chinook were used for the turbine test in 2007, so the agency wanted a comparison of the two turbines using the same species. Future studies may include other species, he said.
Saxon noted that surface passage routes, such as spillway weirs, will continue to be an important part of fish passage. "Turbines designed to improve fish passage conditions may offer opportunities for more flexibility in dam operations and improve tailrace egress conditions for migrating fish," he wrote.
Bonneville Power Administration officials expect that, once two more turbines are replaced at Ice Harbor, the dam will produce an additional 3.5 to 5 average megawatts, although it will vary with water conditions and spill requirements. A 3.5 percent improvement in efficiency for all three turbines should produce an additional 30 to 40 gigawatt hours annually, depending on conditions, BPA spokesman David Wilson said in an email.
"Perhaps of more significance is the improved reliability of these units," Wilson noted, explaining that the turbines and generators being replaced had reliability risks. The three turbines being replaced at Ice Harbor have been in operation since 1961.
Saxon said that the turbine replacements—including design, supply and installation costs—are funded by BPA. The installation contract for $73 million at Ice Harbor includes all options for three turbine runners, new and refurbished turbine components, water passageway modifications and electrical generator replacements.
A similar design and replacement process—also to be funded by BPA—began last year for all 14 turbines at McNary Dam, he said. Designs have not been selected, so costs are not yet determined. Installations could begin in 2025. "The success of the Ice Harbor process and design results for fish passage improvements have been adopted for the McNary design process," he said.