July 11, 2019
By Mike O’Bryant
River temperatures in the tailrace of Lower Granite Dam on the Snake River rose above 67 degrees this week and the air temperature is predicted to rise above 90 degrees this weekend.
That prompted the U.S. Army Corps of Engineers to increase releases of water from Dworshak Dam to keep Lower Granite tailwater temperature under 68 degrees, partially as an aid to the few adult sockeye salmon expected to return to the Snake River and Sawtooth Basin this year.
Anticipating higher air and water temperatures, the Corps increased flows from Dworshak to full powerhouse, or 9,450 cubic feet per second, July 6, and this week added more flow by spilling 3 kcfs beginning midnight, July 10, according to Johnathan Roberts, a water reservoir regulator with the Corps’ Walla Walla District.
He outlined at the interagency Technical Management Team meeting Wednesday, July 10, the Corps’ plans to keep Lower Granite tailwater under the temperature limit set by NOAA Fisheries’ biological opinion for the federal power system.
The BiOp requires the Corps to meet several objectives to enhance salmonids listed under the federal Endangered Species Act, the Corps said in a news release, including maintaining minimum water flows for resident fish and salmon, and releasing Dworshak Reservoir water to maintain lower Snake River water temperatures and help speed juvenile fish (mostly fall chinook) downriver to the ocean.
“We are required to maintain water temperatures at Lower Granite below 68 degrees, if possible, using available reservoir-system management methods,” Roberts said. “It takes about three days for cold-water releases from Dworshak to reach the downstream side of Lower Granite Dam, where the target temperature gauges are located. So, we have to plan well ahead and make adjustments at Dworshak that will be effective at the time we’ll need them further down the river.”
Additional discharges from Dworshak to cool the Lower Granite tailwater have become an annual operation. In 2018, the Corps began to release 12.9 kcfs of the cool water on July 9. As is the case this year, most of the outflow is through the dam’s turbines, with some 3.2 kcfs through a controlled spill, keeping total dissolved gas levels under the Washington state-mandated clean water limit of 110 percent.
Migrating adult sockeye hit a thermal block in 2015 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. IDFG, 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.
Water discharges from the dam on the North Fork Clearwater River prior to the operation was previously at 5,300 kcfs, according to a Corps news release announcing the change.
Downstream of the dam water in the Clearwater River rose by as much as one foot with the higher release.
“With hot weather forecasted to continue, water temperature at Lower Granite is likely to soon exceed 68 degrees if not regulated, creating conditions in the reservoir system that are unhealthy for ESA-listed fish,” Roberts said. “Dworshak’s 43-degree outflows make a big difference in water temperature there and further down the Snake River.”
Cold-water releases from Dworshak will be adjusted as needed to keep temperatures below the BiOp threshold, while conserving as much water as possible, Roberts added.
Idaho Fish and Game biologists had expected few endangered sockeye to return to Idaho this year, and midway through the run, the number of fish crossing Snake River dams is lower than expected, but the exact number of Idaho fish returning is difficult to determine because few of the fish have electronic PIT tags that help biologists monitor the run, according to IDFG.
“With most of the returning Snake River sockeye currently making their way through the Columbia River to Idaho over the next couple of weeks, we should get a better idea of whether our Snake River sockeye salmon were affected by the same processes that led to the downgrade in the Columbia River-wide sockeye forecast at the end of June,” said John Powell, IDFG fisheries research biologist.
The preseason sockeye run size 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).
Some 57,875 sockeye have been counted at Bonneville Dam as of July 9, according to the Fish Passage Center. That’s less than 20 percent of the 10-year average of 294,509 fish. Last year on this date 182,458 sockeye had passed.
Just eight sockeye had passed Lower Granite Dam as of July 8, far lower than the 10-year average of 350 fish.
Of those eight fish, just one PIT tagged fish passed Bonneville Dam, according to Powell. “With only one PIT tag, we are unable to make a precise estimate of the number of Snake River sockeye salmon that are currently in the Columbia River.”
On average about 75 percent of the sockeye destined for Redfish Lake have passed Bonneville Dam on the Columbia River on or before July 4. But Idaho’s sockeye are typically mixed with other sockeye that continue up the Columbia, while Idaho’s fish proceed up the lower Snake River and are counted through its four dams, IDFG said.
“It is still early for most of these fish to have made it to Idaho, approximately 50 percent of the run usually crosses Lower Granite Dam in the two weeks following July 4, thus, we will know more about the size of the Snake River sockeye run in the next couple of weeks,” Powell said.
A major factor in the low forecast and likely low return revolves around how long sockeye spend in the ocean before returning to the Sawtooth Basin near Stanley, according to IDFG. Typically, about 83 percent of IDFG’s hatchery-released sockeye and 75 percent of the naturally produced fish spend two years in the ocean, so most of this summer’s return went to the ocean in 2017.
Post-release survival of young sockeye reared at Springfield Hatchery was the lowest in 2017. Only 16.4 percent survived the downstream migration to Lower Granite Dam, which is still about 400 miles from the Pacific Ocean. Biologists also estimated that 2017 had the second-smallest number of natural-origin juveniles leaving Redfish Lake since 2002.
Idaho’s sockeye face a long and arduous journey. They must travel about 900 miles and 6,000 vertical feet to return to their spawning sites in the Sawtooth Basin. In 2018, the first sockeye arrived to the Redfish Lake Creek trap on July 26.
A total of 276 sockeye crossed Lower Granite Dam in 2018. Of those, 113 completed their migration to the Sawtooth Basin. The 10-year average is 620 sockeye returning to the Stanley area.
TAC left its previously adjusted summer chinook forecast untouched at 34,200 fish. The preseason forecast for summer chinook was 36,345 fish, according to TAC member Stuart Ellis, also of the Columbia River Inter-Tribal Fish Commission. TAC will meet again July 15 to discuss the sockeye and summer chinook runs.
The preseason forecast for Skamania steelhead (April 1 to June 30) was 8,800 total fish of which 3,400 were unclipped, Ellis added. However, the Skamania steelhead return to Bonneville Dam this year was 3,131 total fish of which 1,624 were unclipped.
“We have not started updating the A/B-Index run which goes from July 1-Oct 31,” Ellis said.
The Corps said that Dworshak Reservoir reached recreation pool elevation of 1,598 feet on June 7, offering earlier-than-usual prime water-recreation conditions, with all boat ramps and campsites accessible for visitors.
Park Rangers advise boaters to be aware of potentially hazardous conditions associated with the reservoir being full.
“That means woody debris that is usually beached along the shoreline later during the summer is floating around and can make boating difficult,” explained Colten Shimer, Dworshak natural resource specialist. “Before proceeding at higher speeds, boaters should become familiar with the area and be on the lookout for woody debris or rocks, stumps and shallow areas not visible from the surface.”