Data will be used to help steelhead, Chinook
By Beth Casper
A rainbow trout’s six-second trip over the 463-foot high Detroit Dam is helping scientists learn how salmon will fare on their journey to sea.
For two weeks in July, almost 2,000 rainbow trout were tagged with a radio sensor and two deflated balloons.
One at a time, the fish were sent down a tube directing them through the spillway, a gate at the top of the dam that spills water from the reservoir. After their plunge, the yellow and orange balloons inflate to help researchers recover the fish at the bottom of the dam.
“OK, next fish, No. 154,” said Melanie Sharp, a scientist with Normandeau Environmental and Natural Resource Consultants, during a test last week.
Researchers in boats radioed a fish’s condition back to Sharp: “Minor hemorrhage on one eye and minor bulge on one eye.”
Collected fish were kept in holding tanks for 72 hours to see if their injuries were life-threatening.
For every 20 rainbow trout sent over the dam, a plastic “crash-test dummy” fish goes over as well. The $4,000 device clocks the actual impacts to live fish — things like g-force, changes in pressure and number of collisions.
The data will be used by the U.S. Army Corps of Engineers to meet an important goal: getting a sustainable number of wild spring chinook and winter steelhead in the North Santiam River.
The goal is part of the legally mandated 2008 Willamette Basin biological opinion, which established a set of actions that the Corps and two other agencies need to take to mitigate their impacts on spring chinook and winter steelhead. Those fish were listed as threatened under the federal Endangered Species Act in 1999.
The Corps’ impacts include the 13 dams in the Willamette Basin.
The dams adversely affected Upper Willamette River chinook and steelhead by blocking access to a large amount of their historic habitat upstream of the dams and contributing to degradation of their remaining downstream habitat, according to the biological opinion.
Detroit Dam is the first in the Willamette Basin being studied by scientists to find the best way to help salmon.
Their tests help in two ways: to find the best way for juvenile fish to get downstream around a dam and how best to get the right water temperatures downstream.
Between 2000 and 2005, average temperatures below the dam were 48 degrees in July and 50 degrees in August. Historically those temperatures were between 52 and 56 degrees during those two months.
Spilling water over the dam in the summer helps maintain the historic warmer temperatures downstream. That’s because water at the top of the reservoir has been warmed in the sun, whereas water pulled through the turbines at the bottom is extremely cold.
Spilling water over the dam means money lost. That water isn’t going through the turbines to generate power. The Bonneville Power Administration estimates that the testing has cost about $300,000 in foregone revenue so far. The temperature adjustments started June 1.
Spilling water hasn’t affected the level of water in Detroit Reservoir. That same amount of water would be going through the turbines anyway, said Corps officials.
Preliminary data suggest a 70 percent survival rate for fish going over the spillway, said Greg Taylor, the supervisory fish biologist with the Willamette Valley Project for the U.S. Army Corps of Engineers.
“It’s better than I expected, but in terms of fish passage, it’s not good,” Taylor said. “We may find that it is better than having them go through the (dam) turbines.”
Scientists will study the fate of fish going through the turbines in September.
bcasper@StatesmanJournal.com or (503) 589-6994