The Corps relies on varied operational approaches including spill, turbine improvements, surface passage, bypass and fish transportation systems to address the impacts on fish populations from hydroelectric projects (which along with habitat, hatcheries and harvest, commonly referred to as the four H’s), for an effective fish restoration strategy.
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The Corps has been concerned with fish restoration efforts since 1888, when it warned Congress of an enormous reduction in the numbers of spawning fish in the Columbia River due primarily to harvesters, over-fishing and habitat destruction.
In 1929, regional Corps officials advised that future Corps-built dams provide for the passage upstream of fish, especially salmon migrating to breeding places. In 1934, the Corps assembled teams of internal and outside experts to design fish passage systems for Bonneville Dam.
The Corps applied the lessons learned and decades of research into constructing the dams on the lower Snake River from 1968 to 1975.
Spill is widely recognized as one of the highest survival routes for juvenile fish passage. Water is poured through spillway openings rather than being routed through turbines to generate power or being used for other purposes. Spill has to be carefully managed to avoid gas supersaturation that can be harmful to fish. The Federal agencies responsible for fish restoration recommended using an “adaptive management” approach starting with a spring spill operation that maximizes in-river passage for Snake River spring/summer Chinook until April 20- May 1.
The District transports between 15-22 million fish each year, depending upon run-off and amount of spill.
The Corps began a maximum collection and transport operation using specially-designed trucks and barges to collect Snake River steelhead and late migrating spring/summer Chinook salmon during late spring.
The Corps began barging as an emergency measure in 1977 in the record drought year as a way to move large numbers of fish. In 1978 the Corps modified two barges and started the program, in earnest, in 1981. By 1983 two more barges were built, giving the Corps the ability to barge every day out of Lower Granite Dam.
The transport systems recirculate water, add oxygen and have refrigeration systems that allow us to heat or chill the water. If the water temperature is 65 degrees at Lower Granite Dam and it’s 62 degrees at Bonneville Dam, then over the course of the trip we will slowly drop the temperature to 62 degrees before we release them.
Transporting helps increase fish survivability by putting them on a more natural calendar and helps them bypass potential predators.
Transporting fish gets them back toward their biological clock for the appropriate timing when they should be entering the ocean which enables them to have a better transition to salt water, and hence survival.
Transport is not the total answer to long-term fish population restoration, but it is one tool in our toolbox. There is a time and place for transport, and as we incorporate new technologies like the spillway weirs, we’re reconfiguring the project to accommodate them. We also are building new juvenile facilities and incorporating flexibility into our systems so we can operate the dams to maximize adult fish returns.
The District is pioneering research into surface passage systems that use emerging technologies like spillway weirs to improve fish passage over spillways. In the spring, most juvenile salmon tend to stay in the upper 10 to 20 feet of the water as they migrate downstream to the ocean. Fish migrating during the summer stay deeper.
When approaching dams, juvenile fish dive 50-60 feet to locate fish passage routes such as a spillway opening or juvenile fish screening system. At 1.7 million pounds, 10 stories high and 70-feet long, spillway weirs act as giant fish slides, allowing juvenile fish to pass near the water surface under lower accelerations. It uses less water, which benefits hydropower production, and less spill also reduces the dissolved gas levels in water, which can be harmful to fish.
The first spillway weir was installed at Lower Granite Dam in 2001, and a second was placed at Ice Harbor Dam in 2005. The next two spillway weirs were installed at McNary dam in 2007. In 2008, another spillway weir was installed into Lower Monumental Dam, and in 2009, Little Goose dam had a spillway weir installed. This allowed a surface passage route to be available for downstream migrating fish at each of the NWW FCRPS hydroelectric projects.
Juvenile fish bypass systems, which have operated at the dams for decades, guide fish away from turbines by means of submerged fish screens installed in front of turbines. As the fish migrate downriver, they follow currents and may be attracted by the current created by an operating turbine.
As the fish follow the current towards the turbines, screens guide fish up and into a collection channel in the dam. Fish are then routed either out a bypass outfall or to a raceway for transportation by truck or barge downstream. Estimates of how many fish are guided into mechanical screen bypass systems at dams vary by location (dam, turbine), time (season, day, time of day), species/run, river flow, and powerplant operations.
Fish research is aided by the use of Passive Integrated Transponder, or PIT tags, that are inserted into juvenile fish and read as they pass detectors at the dams. As the tag is read, data about that particular fish is fed into computers that allows tracking of migrating PIT-tagged fish through the river system. That helps researchers determine, for example, which watershed is most successful in returning salmon after smolt release. As for adults, in 2004, improvements were made to provide swim thru antennas for detecting adults as they pass through fish ladders. These electromagnetic field PIT-tag detectors not only enabled researchers to track the progress of individual juvenile fish migrating through the dams downstream, but also tracked them as adults returning to spawning grounds. Adult PIT-tag detectors are in operation Bonneville, McNary, Ice Harbor and Lower Granite dams.
Regardless of hydrosystem operations, fish, sea lions and birds, especially Caspian terns and cormorants, take a large toll on juvenile fish. Several federal agencies were involved in redistributing a Caspian tern colony in the Columbia River estuary, downriver to an island nearer the ocean. The terns, which had consumed 15 million salmonids in 1999, consumed about three million salmon and steelhead in 2004.
Also, a relatively small but stable population of Caspian tern (about 1,000 birds) on Crescent Island above McNary Dam consumed an estimated one million smolts in 2004, including about 35 percent of the Snake River steelhead smolts.
In addition, double-crested cormorants, have increased their take of fish. Their numbers grew from 100 birds in the estuary in 1989 to 18,000 in 2004 when they also consumed an estimated 6.4 million salmonids leading Federal agencies to evaluate alternatives to address this situation.
The Corps has pioneered research for the past 50-years seeking solutions to improve fish survival through the hydrosystem. This effort integrates the technical expertise of biologists and engineers that lead to novel fish passage operations and structural improvements at the dams.
While the Corps continues the spread the risk approach to fish operations, we will continue exploring the development of future spillway weirs and other innovative fish passage options, and pioneering research to ensure the long-term restoration of salmon.