NOAA: Test Results Won't Changeby Mike O'Bryant
The result of investigations conducted early this summer into spillway mortality at Ice Harbor Dam does not suggest that the current spill pattern at the dam needs to be changed, NOAA Fisheries said at this week's Technical Management Team meeting.
The federal fisheries service left the door open for reconsideration at next week's TMT meeting after other fisheries managers have been able to digest the study results. However, spill at Ice Harbor Dam, the only Snake River dam that is still spilling water, is scheduled to end by the end of August anyway.
Researchers found that the modified spill operation set by NOAA Fisheries and the U.S. Army Corps of Engineers June 24 indicated a 96.4 percent survival rate of the PIT-tagged subyearling chinook salmon used in the test. The study concluded July 13. Studies in 2000 and 2002, using the full 2000 biological opinion spill levels, came up with spillway survival estimates of 88.5 percent and 89.4 percent.
The researchers also determined that bypass survival was a high 99.7 percent, while survival through the dam's turbines was 89.3 percent. The combination of the two -- the no-spill operation -- averages to a survival of 94.7 percent, said Paul Wagner of NOAA Fisheries, providing only a 1 percent difference in survival between the modified spill pattern and the no spill option.
Other fisheries managers wondered if the results of the test are strong enough to warrant a change from the NOAA Fisheries 2000 biological opinion spill operations at the dam.
"We still need to look at this data in the context of making changes to the BiOp spill program," said Ron Boyce, Oregon Department of Fish and Wildlife. He argued that the BiOp calls for 24 hour spill at the dam, not the 12 hour nighttime spill that was set in place for the spill test in late June. "We all need to be comfortable with the data before we make the changes."
Wagner explained that earlier spillway survival tests measured mortality when spill gates were set on narrow openings. While that allowed for 24 hour spill, it also resulted in only 89 percent spillway survival. That's why NOAA Fisheries along with the Corps decided this year to study spillway mortality with spilled water going through fewer spill gates and with wider spill gate openings.
"We were uncertain about the results of the test and that's why we split spill -- 12 hours on and 12 hours off," Wagner said.
"You may be getting the higher spillway survival, but you may be lowering survival with just the 12 hour spill," Boyce said. "Why not go to 24 hour spill with this operation (fewer but wider spill gates)?"
"We could just go to no spill," said Scott Bettin, Bonneville Power Administration. "Statistically, there's no difference between this operation and the no spill operation" in terms of mortality.
He added that most juvenile migrants are transported and never get to one of the dams, so the difference in survival between the two in-river routes accounts for few fish. "Statistically at Ice Harbor, the spill versus turbine/bypass is a wash," Bettin said. "We're trying to get to the BiOp performance level of 95 percent. If it's through spill -- great. If it's through the turbine -- great. It looks like we're very close."
There are other factors to consider, such as delay in passage, high temperatures and predation during the delays, Wagner said. "A lot of this is hard to quantify and a lot of the BiOp reflects this uncertainty," he said.
"It's difficult to do these studies and make snap decisions or changes in the BiOp operations while in season," Boyce said. "It's better to complete the study and come to slower operational decisions."
The decision to go to 12-hour spill this year was based on three years of studies, said Cindy Henriksen of the Corps. "We knew there were survival problems and we changed to 12-hour spill based on the best information we have, knowing full well that the flat spill was not a good passage route," she said.
According to fish passage predictions on Columbia River DART (Data Access in Real Time), 91 percent of wild PIT-tagged subyearling chinook have already passed Ice Harbor Dam. Some 97 percent have passed Lower Granite Dam and 94 percent have passed Little Goose Dam, both upstream of Ice Harbor. The passage is 90 percent at McNary Dam. Most of the fish in the river are transported.
TMT will reconsider changes to operations at its meeting Aug. 20, in addition to considering when to end summer spill operations.
In other TMT decisions, both fisheries managers and dam operating agencies agreed to continue to target by Aug. 31 an elevation of 1535 feet at Dworshak Dam, in accordance with the cool water release request of the Nez Perce Tribes and Idaho Department of Fish & Game. Last week TMT had decided to drop flows to 8,800 cubic feet per second, but warm weather in the lower Snake River caused the Corps to keep the Dworshak discharge at 10 kcfs to ensure cool water temperatures at Lower Granite Dam. To meet the 1535 foot elevation, the Corps will drop Dworshak flows from 10 kcfs to 6.5 kcfs midnight Aug. 18. The flow level will remain constant through the month and increase to 8.4 kcfs Sept. 1 through mid-month.
Technical Management Team: www.nwd-wc.usace.army.mil/TMT/index.html
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