Sean C. Morgan
Juvenile and adult steelhead headed downstream in the South Santiam River have their best chance of surviving by taking a trip over the spillway at low pool, researchers have concluded after a study last year.
Scientists studying downstream fish passage at Foster Dam presented their findings from a May experiment on Feb. 7 at Oregon State University during a three-day Willamette Fisheries Science Review conference. Presenting the results were Paul Heisey of Normandeau Associates and Joanne Duncan of the Pacific Northwest National Laboratory.
The study is being conducted as part of an ongoing effort to improve the survival and health of fish that pass over the dam,
During the experiment, researchers sent juveniles and adults over a weir in a spillway and juveniles through the Foster turbines during low pool, 616 feet above sea level, and high pool, 634 feet, to determine their best chance of survival. They tested the turbines at different levels of power production at both pool levels. They also used sensor fish to measure the forces and pressure changes that face fish headed through the turbines and over the spillway.
Overall, about 95 percent of juvenile fish survived while about 90 percent of adult fish survived, although many sustained injuries.
The Foster turbine is unusual among dams in the area, with six blades instead of a typical five. The runner diameter is 100 inches, compared to other dams, which tend to be upward of 200 inches. It also operates at about 257 rotations per minute, a much higher velocity than most other turbines. Data from the experiment were similar to data captured at Sullivan Station, a similarly unusual turbine system. Survival was much lower at both than it is in general through other turbines.
Over the weir, the dam discharged about 160 cubic feet per second at low pool and 187 cfs at high pool. Water was about 2 feet over the weir and 1 foot deep on the chute.
During low pool, 631 juvenile steelhead were released through the turbine and 193 over the weir.
During high pool, 607 juveniles were released through the turbine and 249 over the weir.
During low pool, 55 adults were released over the weir, and at high pool, 49 were released.
As a control, 280 juveniles and 20 adults were released into the tailrace, where water leaves the dam and enters the river.
Through the turbine
Survival rates for juvenile steelhead ranged from 74 percent to 88 percent through a turbine.
The recapture rate for the released fish ranged from 91 to 98 percent.
The lowest survival rate was 74 percent, 111 of 150 fish, at 6 megawatts during low pool. The highest survival rate was 88 percent at about 5 megawatts during high pool.
Researchers found no obvious trend between survival and generation level or pool elevation.
The rate of injury ranged from 18.1 percent to 28.5 percent. The most common injury type was severance or near- severance of body parts on the fish.
Over the Weir
All fish released over the weir were recaptured.
During low pool, all but one juvenile out of 193 survived the trip. All 55 adults survived. The injury rate for juveniles was 6.3 percent., compared to 1.6 percent for adults.
During high pool, 235 out of 249 juveniles survived, while 37 of 49 adults survived. The injury rate for juveniles was 18.1 percent. For adults, the injury rate was 40 percent.
Going forward
The Corps is continuing research this year, installing equipment in the dam during closure of Foster Dam Road scheduled for Feb. 19 to Feb. 22, from 7 a.m. to 6 p.m. daily. The Corps also will repair a trash rack on a water intake.
The Corps is installing temporary sonar equipment to determine how and when fish travel through the dam, said Corps Spokesman Scott Clemans. The sonar has been used at Cougar and Detroit dams.
The Corps learned that fish use both the spillway and turbines at Detroit, Clemans said. At Cougar, they don’t use the spillway because of the temperature control tower there.
At Detroit, fish preferred the spillway when it was open, especially when the water was allowed to flow freely, with the pool elevation just a few feet above the spillway level.
This study will last a year or two and provide a clearer picture potentially to help improve passage.
“Part of the reason for the study is to validate what we’re already doing,” Clemans said. “We’ve been doing this process for many years. Certainly the low pool passage through the fish weir seemed to be very effective.”
During May, the Corps draws down the pool to assist in passage.
During another presentation, the Oregon Department of Fish and Wildlife reported that spring Chinook were passing the dam January through April 2012, and steelhead were headed downstream in October through December.
While the Corps might be able to help the steelhead downstream during October through December, “there may be some operational concerns with doing that,” Clemans said. November and December are key flood control times.
The question is whether there are operational settings for spilling and turbine operation to meet power generation requirements while minimizing the death and injury of juvenile fish, Clemans said.