$50 Million Bonneville Dam Projectby Barry Espenson
A $50 million remodeling project at Bonneville Dam's second powerhouse is expected to draw more migrating juvenile salmon and steelhead away from hydro turbines and deliver them to a safer place in the Columbia River below.
Construction is all but complete on the modification of the powerhouse's trash and ice chute, which has long been a preferred route past the dam.
The alternatives are the turbines or the improved bypass route in which screens steer many of the fish away from turbines and into an enclosed system that delivers them back to the river two miles downstream.
Researchers were called on in 1994 to investigate surface bypass techniques at Bonneville and other dams in the Columbia River system as, potentially, a more benign route.
An investigation of the second powerhouse showed that it did its job of passing the logs, ice and other debris, but that there were "gobs of fish passing through as well," said Blaine Ebberts, lead biologist for the Corps of Engineers on the project.
A study was launched in 1998 that showed nearly 35 percent of the yearling or spring chinook and 50 percent of the steelhead approaching the second powerhouse passed downriver through the sluiceway. It is believed the fish are steered toward the south end of the dam by a huge eddy swirls in a counterclockwise motion.
But while fish passage efficiency was good, it was suspected that survival was less than desired.
The newly completed project earns the sluiceway a new name -- corner collector.
It is expected to improve survival at the powerhouse by from 1 to 3 percent by providing more fish-friendly hydrology and by whisking the fish further downstream where they are less likely to encounter predators.
Together, the improved sluiceway or corner collector and improved screened bypass completed in 1999 are expected to pass 90 percent of the spring migrants and 75-80 percent of the summer migrants, according to a Federal Caucus citizen update. It is estimated that overall survival at the second powerhouse will exceed 95 percent.
The construction answers three separate measures called for in the Reasonable and Prudent Alternative of NOAA Fisheries' 2000 biological opinion on Federal Columbia River Power System operations. Implementing those measures is intended to avoid jeopardizing the survival of salmon and steelhead listed under the Endangered Species Act.
One RPA action specifically calls for construction of the corner collector "if, and as soon as, evaluations confirm the optimum design configuration and survival benefits."
The other two actions call for investigations of high-flow outfall and to increased entry rates of fish approaching surface bypass/collector entrances.
"We think it's going to be pretty successful," said Steve Rainey, a NOAA Fisheries hydraulic engineer. Corps, NOAA Fisheries, experts from other fishery agencies will finalize during the coming month study designs that will pin down survival through new fish passageway.
"Our job is to keep as many fish out of the turbines as we can," said Rainey. Despite the fact that the second powerhouse turbines are perhaps the least lethal in the hydrosystem, it is still more deadly than the other routes.
The second powerhouse's eight turbine units and its initial screened bypass system were completed in 1982. But the system provided low fish guidance efficiencies so at times it had been shut down during the migration season to avoid undesirable turbine passage. With the passage improvements, the second powerhouse will now be the operational priority during migrations.
The modifications on the south end of the powerhouse start with the modification of the upstream gate of the sluice chute. The bottom sill of the chute is at an elevation of 52 feet. The old gate could be lowered to an elevation of 68 feet to allow accumulated trash or ice in the forebay to pass downriver. The water, trash and fish flooded through at a rate of about 2,200 cubic feet per second. The forebay elevation is normally held between 74.5 to 76.5 feet.
The new gate pulls up, allowing a taller column of water, down to the 52-foot elevation level, to surge down the chute -- about 5,000 cubic feet per second. It is believed that the increased volume will also increase the fish passage efficiency, but only time will tell. The system was "watered up" two weeks ago, but the first live test will be in March when Spring Creek Hatchery, located just upstream, releases juvenile chinook into the river, said Rock Peters, head of the Anadromous Fish Evaluation Program for the Corps' Portland District.
Ebberts said that the system was already quite efficient considering the route had employed only 2,200 cfs compared to a powerhouse capacity of about 160,000 cfs.
"Proportionwise, you're getting a lot more fish with a lot less flow," he said. That compares to 50 percent fish passage at the spillway, where as much as 75,000 to 150,000 cfs is spilled.
Though doubling the flow won't likely double the efficiency, "it certainly will not be any less efficient," Peters said. Survival studies are planned for the spring and summer at the corner collector, as well as the other passage routes at the two powerhouses and through the spillway.
A concrete "ogee" was constructed the entrance of the corner collector. It is designed to create a more natural, benign flow during the transition from the forebay, down into the conveyance channel.
That concrete channel, which is 15 feet wide and 20 feet deep, stretches some 3,000 feet to beyond the western tip of Cascades Island. In all, about 36,000 cubic yards of concrete was used in the project. Construction contracts were awarded in July of 2002 with construction beginning about one year ago.
Project manager John Kranda said he expected the project costs to total from $45 million to $50 million. That includes survival studies during the next two migration seasons. It is funded through the Corps' Columbia River Fish Mitigation Program. Money for the program is appropriated by Congress. Most of the expenditures are reimbursed to the U.S. Treasury by the Bonneville Power Administration, which markets power produced at the federal dam. The Corps and Bureau of Reclamation operate the FCRPS dams.
"The big money last year was the corner collector," Kranda said. The project absorbed nearly $29 million during fiscal 2003. The CRFMP appropriation was $85 million, minus about 16 percent savings and slippage to bring mid-year estimates of available funding to $73.3 million.
The 5,000 cfs outfall enters the river at about 20 feet per second, sandwiched between the flows gushing from the powerhouse to the north and those from the spillway to the south. A 50-foot-deep plunge pool was excavated at the outfall to cushion the fishes' fall.
That outfall was designed to create a large plume across the middle part of river where currents are strong. That will discourage northern pikeminnow and other fish and avian predators. Pikeminnow and other predators are known to congregate near dam tailraces, because of known concentrations of salmonids emerging from turbines and bypasses. Some of those fish can be dazed from the passage and, as a result, easy prey. The old trash and ice chute outfall was just below the dam.
With the expected rapid dispersal of the fish in mid-river, they won't be as concentrated. And they'll be in a stronger current, making things difficult for the weak-swimming pikeminnow.
"You've distributed the fish (salmon) across almost the full width of the river," Ebberts said. The flow pattern was designed so that the plume would not extend to within 100 feet of either bank. Pikeminnow, particularly, spend most of their time in those nearshore areas.
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