Environmental Science & Engineering - www.esemag.com - May 2004
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High-flow, low-head pumps provide safe passage for pacific salmon

The pump station at the Rocky Reach Dam is being constructed to accommodate 30 horizontal flow pumps for a combined capacity of 6,000 ft3/second.

As part of a plan to safely guide juvenile salmon on their journey down Washington State’s Columbia River to the Pacific Ocean, a fish bypass system at the Rocky Reach Dam is being equipped with 29 ultra-low head, high-capacity submersible pumps and auxiliary equipment from ITT Industries’ Flygt unit.

Described as the ultimate water slide, the project will cost close to $160 (US) million, an investment for fish, not humans. It is Chelan County Public Utility Department’s way of getting migrating, juvenile salmon safely around Rocky Reach Dam en route to the ocean, while maintaining the dam's original charter - its ability to generate power.

The project will be the most expensive fish bypass on any Columbia River dam upriver of the Tri-Cities. At stake is millions of dollars in electricity, fish survival, and the dam's operating license.

Beginning in the ice fields of the Canadian Rockies, the Columbia River flows for over 1,200 miles to the Pacific Ocean. It is the fourth largest watershed in the United States, draining 259,000 square miles and receiving waters from seven states and two Canadian provinces. The Columbia River has the second largest volume flow of any river in the United States.

It generates electric power, provides irrigation, and harbours deep-water ships that come and go across the Pacific. Millions of people depend on the river for employment in water-related industries, and for transportation.

The Columbia River Basin has historically produced some of the world’s largest runs of salmon. Estuarine habitats provide important nursery and rearing areas for young salmon, and adults use them as temporary holding areas during their return migration from the ocean to upstream spawning areas.

While a great many factors have contributed to the decline of salmon stocks in the Columbia River Basin, dams clearly have had a significant impact, including those through which fish passage is provided but at reduced levels from natural conditions. Overall populations of the basin’s salmon fish stocks are estimated at less than 10 percent of their historic size, despite major hatchery programs.

Providing a safe passage for juvenile salmon on their run to the sea - while at the same time allowing enough water to pass through the dam’s turbines to generate electricity - was a problem at the Rocky Reach Dam. Some 473 miles up the Columbia River from the Pacific Ocean, Rocky Reach Dam was constructed in 1961, providing the region with 1347 total megawatts of electricity.

Man-made “fish ladders” have long helped salmon navigate past dams during their upstream migration. The downstream migration of fish in US rivers, known as “smolting”, was severely affected over the years due to a lack of cost-effective hydro turbine bypass technology. This has resulted in a fish mortality rate of between five and eight percent, and with some of the bigger rivers in the US having as many as 50 dams along the path of the migrating fish, there has been a significant decrease in fish numbers.

Environmental and legislative pressures have increased in recent decades. Legislation now mandates that owners and operators of hydroelectric dams either set mandatory spill periods during peak migration season, which results in a major loss in power production, or install devices to aid downstream fish migration. These devices, known as fish attraction systems, are used to lure and then divert juvenile salmon, steelhead and other endangered species away from the hydroelectric turbines to a transport pipe running through the dam and then out to safety.

The fish attractor at Rocky Ridge is powered by new low-head, high-flow Flygt pumps.
Swimming downstream, salmon “go with the flow”. That means they could be pulled into the fast-moving hydroelectric turbines at power plant dams. At the Rocky Reach Dam, the Chelan County Public Utility Department is constructing a very large “fish attractor” intended to allow the fish to bypass the turbines safely via a four-foot diameter tube.

“Scientific studies show that salmon prefer certain depths of water and velocities,” says Stefan Abelin, director of Engineering at Flygt’s US operation in Trumbull, Connecticut.

“The fish attractor is aimed at creating conditions to attract the fish toward the bypass system and away from the turbines.”

In ongoing research in this field it was found that the best results are achieved by using pumps; however, no pump existed that would handle the high flow rate at an extremely low head, with the required efficiency rate. In 1998, ITT Flygt began development work on a new horizontally installed propeller pump, which would be able to meet the required duty points. And after thousands of hours of CFD modelling and scale model testing, a new pump design was created. The pump utilizes a planetary gear reducer to match the motor speed with the propeller rpm.

The fish attractor at Rocky Ridge is powered by these new low-head, high-flow Flygt pumps. The pump station is being constructed to accommodate 30 horizontal flow pumps for a combined capacity of 6,000 ft3/second. The 90 kW propeller pumps have a flow rate of 7.0 m3 per second at a head of 0.55 metres, providing a combined flow rate of 175 m3 per second. The auxiliary equipment includes 10 racks of flap gates to prevent reverse flow, electric controls, remote supervision, control buildings, transformers, pump testing, installation, plus an extended pump and control maintenance agreement.

The Rocky Reach Bypass System is the first full-scale fish attraction project ever undertaken. The Chelan County Public Utility Department hopes the new bypass will let it phase out all of its spills except for a 16 percent spill for 40 days each spring for Sockeye salmon which tend to travel too deep to use the bypass.

The Public Utility Department says the slide bypass will save money because the utility will not have to spill as much water to make sure the fish can migrate past the dam. That water instead can be used to generate electricity. The public utility lost $14.2 million in power production at Rocky Reach in 2000 due to spills for all species of salmon and steelhead.

Without the system, Rocky Reach would have to spill 60 to 70 percent of its average daily flow in the spring and summer, costing an estimated $934 million in power production over the 15-year financial life of the new system.
For more information contact: www.flygt.com.

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