The U.S. Army Corps of Engineers will focus on operational changes—such as flexible spill—in the Federal Columbia River Power System to improve salmon and steelhead survival now that the majority of structural improvements have been made, Corps' fish program manager Tim Dykstra told the Northwest Power and Conservation Council.
Dykstra outlined some of the major structural improvements made over the last five years in a May 13 presentation to the Council, and concluded, "By and large, I think much of the low-hanging fruit has been plucked in terms of overhauling for fish passage."
He said that before 2008, the Corps had been working to optimize fish-passage conditions, but the overhaul intensified with the 2008 BiOp, which began a series of improvements at all of the Corps' main-stem lower Snake and lower Columbia river dams. Major projects were aimed at improving fish-passage conditions, with a special focus on juveniles, he said.
The overhaul has been primarily funded through the Corps' Columbia River Fish Mitigation Program, which requires upfront appropriations from Congress and is paid back over time by BPA, he said.
Dykstra said several major projects to improve fish-passage conditions at eight Snake and Columbia river dams were outlined in the 2008 BiOp, including improvements to surface passage with structures like removable spillway weirs and corner reflectors; improvements to juvenile bypass systems, like repositioning outfall pipes so juvenile fish spill into deeper parts of the river where predators are less prevalent; and other advancements, such as a spill wall at The Dalles Dam, which has improved survival rates.
He provided details on five large projects completed over the past five years, including water cooling structures at Lower Granite and Little Goose dams' fish ladders; reconstruction of Lower Granite's juvenile bypass system; an adjustable weir at Little Goose; turbine replacements at Ice Harbor Dam; and a new PIT-tag detection system at the Lower Granite spillway.
The water-cooling structures at Lower Granite and Little Goose are designed to prevent the delayed migration of adult salmon and steelhead, which sometimes occurs when water temperature in fish ladders warms, or when the differential between water below the dam and above the dam is too great. To solve that issue, the Corps installed a large pipe that brings cooler water from the depths of the river to the surface, and sprays it out near the fish ladder exit. The opportunity to use the method at other dams is diminished, since cool water releases from Dworshak Dam on the Clearwater River sends the cooler water to Lower Granite and sometimes to Little Goose, but the impact diminishes farther downstream, he said.
Since the project was completed in 2016 at Lower Granite, the ladder exit has cooled to an average of 66.2 degrees, or 2 degrees cooler than it was prior to completion, he said. The temperature differential between the surface forebay and tailwater was reduced to 1.2 degrees, he said.
At Little Goose Dam, the ladder exit has cooled to an average temperature of 66 degrees, or 1.7 degrees cooler than it was before the upgrade was completed in 2018, and with minimal temperature differentials, he said. "This was an important project for us, and we're happy with the results," he told the Council.
The Corps also reconstructed Lower Granite's juvenile bypass system, one of many juvenile bypass systems overhauled at Corps dams. The changes included enlarging pipes where fish pass from 10 inches to 14 inches; widening and smoothing edges in the juvenile collection channel; installing a new transportation channel and flume; and moving the outfall away from shore to a deeper location in the river.
Dykstra said total survival through all passage routes at Lower Granite Dam now exceeds BiOp goals, with more than 97 percent of yearling Chinook, 94 percent of subyearling Chinook and 99 percent of juvenile steelhead surviving the journey. "For the bypass system itself, we're nearly 100 percent for this new system," he said. "I think the end result has been a significant improvement for fish."
Another improvement at Little Goose Dam that became operational in spring 2018 was the installation of an adjustable spillway weir, which allows water—and juvenile fish—to pour over the dam at the surface, where most juvenile fish are found, Dykstra said. He said before the improvement, it took a crew of at least three people about three days to change the weir from a low crest to a high crest position as river flows changed. The switch can now be made in less than 30 minutes with a press of a button in the control room, he said.
One of the Corps' ongoing projects is to replace turbines as they age with newly designed turbines that increase power generation and minimize the risk of trauma to juvenile fish that pass through them, Dykstra said.
Last May, the Corps commissioned a new fixed-blade runner at Ice Harbor Dam that was designed to reduce the risk of injury to fish caused by strike and shear, and to reduce pressure differentials that cause trauma to fish. Installed in Unit 2, the turbine has been tested with balloon-tagged fish. Dykstra said 98 percent of the fish that passed through the turbine were still alive after 48 hours (known as direct survival). About 1.5 percent of the fish had visible injuries, compared to 3.8 percent with visible injuries after passing through the old turbine, he said.
Installation is underway to replace the turbine in Ice Harbor's Unit 3 with an adjustable-blade runner of the same design, and completion is expected in fall 2021. Unit 1 is scheduled to get a new adjustable-blade runner in fall 2023, and plans are being made to replace turbines at McNary and John Day dams after that, he said.
Lastly, after years of research and development, a new PIT-tag detection system at Lower Granite Dam was completed in December, and is expected to dramatically increase survival information for the region.
Dykstra noted that the 2008 BiOp called on the Corps to conduct a feasibility study to determine if it's possible to detect juvenile PIT-tagged fish going over a spillway.
At most dams, researchers use PIT-tag data from fish traveling through fish bypass systems to determine survival rates and conduct other studies, and have to assume fish not detected in a bypass system went over spillways. But as more projects spill more water, far fewer fish are being detected, so studies are less reliable because they're based on small sample sizes.
Gordon Axel, research biologist for NOAA's Northwest Fisheries Science Center, explained the project to the Council, noting the many challenges of detecting the tiny transponders embedded in fish traveling at velocities up to 79 feet per second down the spillway.
He said so far, since spring spill began on April 3, efficiency of detection is ranging from 45 to 65 percent at each of three rows of antennas, with some fish detected as many as three times. To date, the Corps has detected 114,000 fish, compared to 18,000 fish traveling through the juvenile bypass system, Axel said.
Installed in one of the spillways, the new system has already boosted detection by nearly 500 percent, he said.
Asked if the Corps is thinking about installing other spillway PIT-tag detection systems at other projects, Dykstra said it depends if it is critical for gaining new understanding of survival. He said the Corps isn't interested in building new infrastructure just for the sake of detecting more fish. "We're keenly interested in learning. If that means it's critical we add more spillway detection capability—if that's really the critical piece—we're willing to explore that and pursue that," he said.
Overall, Dykstra said, the Corps is wrapping up this chapter of making structural changes to benefit fish passage, as called for in the 2008 BiOp.
"We've done about all that can be done in terms of infrastructure changes," he said. "As we transition now to a different paradigm, we're transitioning to a program that really takes advantage of that past investment," which includes making changes to operations to further the effort to improve fish passage, he said.