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Study Measures John Day Spill Regime Efficiency by Mike O'Bryant Columbia Basin Bulletin - November 22, 2002

Tests of fish passage efficiency at John Day Dam this year show that most juvenile salmon pass the dam at night, giving credence to NOAA Fisheries' 2000 biological opinion recommendation to spill 60 percent of the river at night.

However, another test shows that juveniles that pass through the dam's juvenile bypass system will spend considerably more time in the churning waters near spillways at 60 percent spill than when the dam is spilling 30 percent of the river.

Scientists presented the results of the three studies at this year's four-day Anadromous Fish Evaluation Program review in Portland, which was sponsored by the U.S. Army Corps of Engineers.

John Beeman of the U.S. Geological Survey said that daytime fish passage efficiency (FPE), defined as the proportion of fish passing the dam via all non-turbine routes, is better when 30 percent of the river is spilled 24-hours a day than it is with 12-hour spill in which no spill occurs during the day and 60 percent spill occurs at night (BiOp spill), an indication that spill helps fish pass dams, but that there are few fish that pass in the daylight.

However, in a test using radio-tagged juvenile salmon, Beeman, along with H.C. Hansel, P.V. Haner, S. Juhnke, L. Dingmon, L. Kelley and J. Phelps, found that FPE overall was greater in the spring for yearling chinook during 12 hour spill than with 24 hour spill by 84 percent to 80 percent.

"The difference in FPE of yearling chinook salmon was a result of significantly greater juvenile bypass system passage during the 12-h treatment, as no significant difference in SPE was evident between treatments," according to the report's abstract. SPE is spillway passage efficiency, defined as the proportion of fish passing via the spillway.

The study also found that forebay residence times decreased as spill increased, but that there was still little difference overall between 12 and 24 hour spill for both yearling spring chinook and for steelhead. Sub-yearling chinook pass the most readily, Beeman said.

According to a hydroacoustic study that also looked at 12 and 24-hour spill by Kenneth Ham and Russell Moursund, the number of fish passing the dam increased at about 9:00 p.m. At night, lots of fish pass and the study found a significant increase in passage during 60 percent spill over the 30 percent spill for yearling and sub-yearling chinook.

Overall spring fish passage efficiency during 24-hour 30 percent spill was 89.3 percent (plus or minus 2.4 percent), while the nighttime 60 percent spill was 93.8 percent (plus or minus 2.5 percent). Summer fish passage efficiency was lower, but had a similar spread between the two spill regimes. 24-hour spill passage efficiency was 88 percent (plus or minus 0.9 percent), while 12-hour spill passage efficiency was 91.6 percent (plus or minus 1 percent).

Scientists also looked at fish passage through turbine number seven where an extended length submerged bar screen was installed and found little difference between the two spill treatments in fish guidance efficiency, spill passage efficiency and spill passage effectiveness.

Another study looking at the movement of juveniles that pass through John Day Dam's fish bypass system found that juveniles will spend about twice as long in the dam's tailrace area at 60 percent spill than those that pass while spill is at 30 percent of the river. Ben Hausmann, T.L. Liedtke, C.D. Smith and Beeman, all of the U.S. Geological Survey, found that yearling chinook in the spring spent an average of 23 minutes in the tailrace area at the higher spill level and 11 minutes in the area at 30 percent spill. Yearling steelhead spent 25 minutes in the area at 60 percent spill and 12 minutes at the lower spill amount.

"With higher spill, there was a tendency for fish coming out of the outfall to stick around the spill zone," Hausmann said. "With the 30 percent spill, there was a tendency for the fish to travel more directly down stream."

Summer results were similar, with travel times for the higher spill about 1.5 times more than 30 percent spill. However, juveniles were closer together in time the further down river they traveled, according to Hausmann. The study made no conclusions as to the harm the longer travel times may have on the fish.

Related Links:
U.S. Army Corps of Engineers: AFEP