August 10, 2018
With air temperatures expected to exceed 100 degrees Fahrenheit this week in the Clearwater and Snake river basin, the U.S. Army Corps of Engineers Monday increased flows of cold water from Dworshak Dam from about 10,000 cubic feet per second to 13 kcfs.
Dworshak is located on the North Fork of the Clearwater River and the dam’s cold water is used to cool the tailwater downstream in the Snake River at Lower Granite Dam, but the cold water takes about three days to arrive at Lower Granite, according to Steve Hall of the Corps’ Walla Walla District.
Hall told the interagency Technical Management Team meeting Wednesday, August 8, that air temperatures in the lower Snake River were expected to reach 105 degrees Wednesday, 111 degrees Thursday and 105 degrees Friday, causing an expected rise in Lower Granite tailwater temperature. Air temperatures in the basin are expected to exceed the average through September, he said.
Dworshak water is used to hold the dam’s tailwater temperature at or below 68 degrees to improve the migration of adult salmon and steelhead.
Complicating that cooling process is up to 24 kcfs of “very warm water” from Idaho Power’s Hells Canyon Dam, Hall said, as the utility generates more power to sell into the power market, largely to help meet air conditioning demand.
Surface water temperature in Lower Granite’s forebay just upstream of the dam is consistently over 70 degrees and the dam’s removable spillway weir is passing 75 degree water, Hall said.
Temperatures increase further downriver all the way through McNary Dam on the Columbia River, according to Charles Morrill of the Washington Department of Fish and Wildlife.
As it turns out, very few fish are currently passing the dam. Just 268 endangered Snake River sockeye salmon have passed Lower Granite so far this season and the run is just about over, according to Russ Kiefer of the Idaho Department of Fish and Game. Further upstream in the Stanley Basin the first sockeye was trapped July 26 and as of Sunday Aug. 5, 26 have been trapped, Kiefer said. Three of the fish are wild/natural.
Daily steelhead passage at Lower Granite is averaging about 35 fish and daily summer chinook salmon passage is averaging in the mid-20s. No fall chinook have arrived at the dam.
In addition, juvenile subyearling chinook passage downstream is about 1,000 fish per day, according to NOAA Fisheries’ Paul Wagner.
“As we get into September, fall chinook and steelhead will become a more significant concern,” Hall said, adding that saving some of the Dworshak water in August will aid those runs later.
He said that to hit the elevation goal of 1,535 feet in the dam’s reservoir at the end of August, output at the dam will need to average 8.7 kcfs through the remainder of the month.
“You need to consider which approach with limited resources you want to take,” Hall told TMT’s salmon mangers. “We can hope there will be a cooling trend, but that’s not predicted. Or, you can make a conscious decision that more water later would be more valuable, giving you greater flexibility later.”
Fish managers opted to search for ways to save the water for later. They asked that the Corps turn off the RSWs at Lower Granite and Lower Monumental dams and for the Corps to target 68 degrees in Lower Granite’s tailwater.
Although the federal Columbia River power system biological opinion calls for an upper limit of 68 degrees, in modeling water temperature weekly and sometimes daily, the Corps has been targeting 67 degrees in the dam’s tailwater.
“If there is an opportunity to save water, then use it (reduce flow at Dworshak) without having to contact TMT,” Wagner said.
The Corps this week announced in a press release that flows from Dworshak Dam are expected to fluctuate between 5 kcfs and 13 kcfs through August.
“This process of releasing cool North Fork Clearwater water from Dworshak Reservoir to improve fish passage in the warmer water of the Snake River is part of the Federal Columbia River System’s (FCRPS) ‘salmon flow augmentation’ program,” the Corps said. “The Corps implements this part of the program annually, starting during the summer when water temperatures increase, and ending in early fall when water temperatures begin to cool naturally. The flow augmentation program allows blending of this cooler water with the warmer water arriving from the upper Snake River as it passes through Lower Granite Lock and Dam.”
The BiOp requires the Corps, Bureau of Reclamation and Bonneville Power Administration to comply with mandated water-management actions to enhance ESA-listed fish survival on an annual basis, including:
- Release salmon flow augmentation water to benefit resident fish and salmon.
- Release cold reservoir water to maintain lower Snake River water temperatures below 68 degrees to improve conditions for adult salmon and steelhead migrating upstream to their spawning grounds.
- Manage total dissolved gasses to not exceed 110-percent saturation. When water spills over the dam, gas is entrained and held in solution due to pressure differences in the water at depth. High TDG levels can be stressful for fish, the Corps said.
Flow augmentation of 200,000 acre feet of water is important to tribes, said Jay Hesse of the Nez Perce Tribe. Even with that water, he said, fish are experiencing pre-spawn mortality. He added that the 200 kaf is distributed over 15 days of decreasing flows beginning at about 8 kcfs and rapidly ramping down.
In addition, with high temperatures in the Tri-Cities area and rising demand for air conditioning, Ice Harbor Dam may need to increase its generation above the current minimum generation level to meet the Tri-City electricity demand, said Tony Norris of BPA. More generation means less spill at the dam.
“The demand in the Tri-Cities was over 10 megawatts yesterday (Tuesday this week) and its possible they may need more to keep the lights on,” Norris said. “Conditions should ease Friday.”
Norris was uncertain whether the additional generation would be needed.
--CBB, July 27, 2018, “River Managers Ponder Passage Gaps For Snake River Sockeye At Lower Snake Dams,” http://www.cbbulletin.com/441185.aspx
--CBB, July 13, 2018, “With Temps Rising, Corps Cools Snake River With Dworshak Water To Aid Endangered Snake River Sockeye,” http://www.cbbulletin.com/441108.aspx
-- CBB, June 12, 2015, “NOAA Fisheries Releases Snake River Sockeye Salmon Recovery Plan: 25 Years Of Actions At $101 Million” http://www.cbbulletin.com/434233.aspx