July 18, 2019
A system operational request brought to the interagency Technical Management Team this week by fisheries managers and approved by both fisheries and hydro managers helps clarify priorities for the use of cool water from Dworshak Reservoir on the North Fork of the Clearwater River in Idaho.
Each July and August, Dworshak’s 43.5 degree water (the temperature deep in the reservoir this week) is used to maintain temperatures at under 68 degrees Fahrenheit downstream in the lower Snake River at Lower Granite Dam. That is the upper temperature allowed in Lower Granite’s tailwater, according to NOAA’s 2019 federal Columbia River power system biological opinion.
The SOR (#2019-1), the first of the year, is based on that BiOp, helping to clarify operations at Dworshak through August and into September.
Last week, river temperatures at Lower Granite rose above 67 degrees and air temperatures rose, prompting the U.S. Army Corps of Engineers to increase releases of water from Dworshak Dam to aid the few adult sockeye salmon expected to return to the Snake River and Sawtooth Basin this year, as well as adult spring/summer chinook, steelhead and fall chinook. In addition, the cool water helps migrating juvenile fall chinook salmon, according to the SOR.
Snake River sockeye salmon are listed as endangered under the federal Endangered Species Act. In 2015, sockeye hit a thermal block as river temperatures rose considerably above the 68 degree F limit. Some 90 percent of sockeye died before reaching Ice Harbor Dam, the lower of the four Snake River dams. Idaho Fish and Game, NOAA Fisheries and the Nez Perce Tribes set up a rescue project at Lower Granite Dam to trap the adults and haul them to the hatchery at Eagle, Idaho.
The preseason sockeye run size for the entire Columbia River basin was downgraded by one third to 62,800 fish based on the recent 5-year average run timing at Bonneville Dam. The preseason forecast was 94,400 fish. The U.S. v Oregon Technical Advisory Committee met July 8, downgrading the expected sockeye run (most of those sockeye will travel to mid-Columbia River tributaries, with few turning into the Snake River).
Sockeye numbers into the Snake River are low again this year. Just 19 had made it to Lower Granite by July 17, just 3 percent of the 10-year average of 693 fish. Last year on this date, 167 sockeye had passed the dam.
Flows from the dam were increased to 9,450 cubic feet per second July 6, which is where it stood Wednesday during TMT’s meeting.
This week, according to Jon Roberts, a water reservoir regulator with the Corps’ Walla Walla District, cooling was expected Thursday and Friday and that will help drop the temperature at Lower Granite to about 66 degrees. However, warming by late weekend and continuing into early next week is expected to heat the river up once again. The temperature in Lower Granite’s tailwater as of Thursday morning was 66.9 degrees.
“With that forecast, we will begin to spill water (Thursday, July 18),” discharging 13.1 kcfs from the dam. Water over 9.45 kcfs is spilled and that will increase total dissolved gas levels downstream and at nearby hatcheries. The 13 kcfs flow with spill will continue until Friday, July 19, and then go to 14 kcfs to compensate for the upcoming 100 degree temperatures, Roberts said.
“We want to push as much water as we can while its cool,” he said. “With the higher temperature, TDG will go up close to 110 percent, the Washington state upper limit for TDG.
He added that Dworshak would be at least at full powerhouse through August and the reservoir would drop to an elevation of 1,535 feet, but it would have little cool water left for September.
While they want cool temperatures in the Lower Granite tailwater, fisheries managers also want Dworshak water for flow augmentation and cooling into September.
The SOR “seeks to have Dworshak summer (July and August) discharge management prioritize temperature management when allocating available water,” the SOR says. “As such, 1,535’ on August 31st should be viewed/treated as the limit for maximum drawdown, not as a target. After August 31st, water above the 1,535’ elevation (if any) would be added onto the Snake River Basin Adjudication Dworshak Dam release of 200 Kaf (200,000 acre feet) and used to extend water temperature management as far into September as possible, while still achieving a 1,520’ pool elevation by September 30.”
BiOp actions for Dworshak summer water discharges target both temperature for cooling and for flow augmentation, the SOR says. It cites pages 38 and 39 of the BiOp, which says “Once the reservoir is refilled, Dworshak is operated in the summer for the gradual evacuation of water through a combination of temperature objectives to maintain Lower Granite Dam tailwater temperatures below 68° F and reach an elevation of 1535 feet by August 31 and elevation 1520 feet by September 30.”
The SOR says that “Fisheries managers support the use of Dworshak discharge to meet the Lower Granite Dam tail-water temperature criteria to not exceed 68°F between July 1st and August 31st. However, there are also biological benefits for applying cooling water for adult migrants in September. Cool water releases in September maintain a cool migratory corridor and holding areas in the lower Snake River below Lewiston, Idaho, and in the Clearwater River (including fish being held at Nez Perce Tribal Hatchery) for pre-spawn adult salmon, steelhead, and lamprey.