Columbia Basin Bulletin: Dworshak Unit Out: River Managers Mull Options To Maintain Cool Conditions For Snake River Salmon
Friday, August 22, 2014
A primary source of cool water used to improve Snake River salmon summertime migration conditions was pinched Aug. 15, leaving fish and hydro system management representatives to debate how to make the best out of a bad situation.
Unit 3 at Dworshak Dam – the largest of the three generating units at the dam in terms of water passing capability-- went out of service at 3:30 p.m. last Friday due to a ground fault that resulted in a reduction of outflow from 9,800 cubic feet per second down to 6.5 kcfs. That 6.5 kcfs total includes about 2 kcfs released through spill gates to replace a part of the roughly 5.5 kcfs in flow lost when Unit 3 was shut down.
From a fish migration perspective, running as much cool water as possible through the turbines is a preferred option because that operation stirs up little total dissolved gas in the river below while helping improve migration conditions.
Another water release option is spill. It creates more TDG that can at higher levels threaten fish health.
Federal, state and tribal fish managers on Wednesday asked the U.S. Army Corps of Engineers, which operates the dam, to push up spill to restore outflows to previous levels of about 10 kcfs in order to increase the probability that water temperatures downstream will be at desired levels.
Signed on to the “system operational request” are the National Marine Fisheries Service (NOAA Fisheries), the U.S. Fish and Wildlife Service, the Oregon Department of Fish and Wildlife, the Washington Department of Fish and Wildlife, the Colville Tribes, the Nez Perce Tribe and the Columbia River Inter-Tribal Fish Commission. A spokesman for the state of Idaho said it would not object to the proposed operation.
Such a boost in spill would create more TDG than is allowed under water quality guidelines. But the SOR signees suggest that the Corps seek temporary waivers from the state of Idaho and the Nez Perce Tribe that would allow a discharge of up to 10 kcfs, which is estimated by the Corps to produce TDG levels of up to 120 percent. The state standard is 110 percent.
Getting the desired water out and holding down TDG levels to water quality limits might be impossible.
“Something has to give,” said the state of Idaho’s Russ Kiefer.
As of late Thursday the issue was being discussed by Corps policy level and legal staff to decide whether to stay its current course, deny the SOR or implement something in between.
The Corps has said that a time for a return of service of the turbine unit is unknown but the earliest date could be Monday, Sept. 1. Likely it would take longer to return to service.
As of Tuesday the average total outflow was 6.7 kcfs allocated via 4.4 kcfs in power (units 1 and 2) and 2.2 kcfs in spill with an average forebay elevation of 1552.64 feet. That volume at this time has served to keep TDG levels just below 110 percent, the cap set for Dworshak operations under the state of Idaho’s water quality regulations.
Dworshak is located in west central Idaho on the North Fork Clearwater River about three miles upstream from its confluence with the Clearwater River, which feeds into the Snake.
Spill was started at the dam following the unit breakdown in order to push as much water through the dam as possible to augment flows for salmon spawners headed up upriver, and for whatever juvenile migrants that might be in the river on their way toward the Pacific Ocean.
Cool waters from Dworshak’s depths are called on late each summer to bring down water temperatures in the Snake, and in particular flows through Lower Granite Dam’s reservoir and the dam itself. A goal is to hold water temperatures in Lower Granite’s tailrace and in the fish ladder at or below 68 degrees.
In its most recent model run based on water conditions and weather forecasts its was estimated that a flow from Dworshak of 7 kcfs “can maintain temperatures at around 66 degrees Fahrenheit, with reasonable assurance,” the Corps’ John Heitstuman told the Technical Management Team Wednesday. He stressed that those conditions are, of course, subject to considerable change depending on the weather and other factors.
The TMT, made up of federal, state and tribal fish and hydro managers, during a Wednesday meeting spent more than four hours discussing potential solutions. Fall chinook passage is just beginning and Lower Granite tail water temperatures, which have largely been held in check, have held at slightly below 68 degrees.
The Lower Granite ladder also holds a fish trap where fish are collected for sampling and for broodstock. Many of the passing fish this time of year are wild Snake River fall chinook that are listed under the Endangered Species Act.
The fall chinook are headed farther up the Snake, the Clearwater and other tributaries. Because of their listed status, many of the Snake River fish, both fall chinook and steelhead, are the subject of numerous research studies collecting data aimed at tracking their comings and goings, their condition, their status and other information. Considerable data is collected at the trap through the reading of electronic and other tags and hands on evaluations.
Much of the research is called for in NOAA Fisheries’ Federal Columbia River Power System biological opinion, which also requires that Dworshak be used to augment flows in summer by drawing down the reservoir from full pool of 1,600 feet elevation (it is a goal to fill the reservoir for the Fourth of July holiday) down to 1,535 by the end of August.
The drawdown toward 1,535 was on track, passing nearly 10 kcfs most days since early July through the three generators with occasional spurts of spill during periods coinciding with hot weather that brings up water temperatures.
But the loss of Unit 3 made reaching the 1,535 mark by Aug. 31 impossible even with total turbine-spill output at 10 kcfs, according to Corps officials. The water passed through spill gates over the past week has made up for about one-third of the loss from the Unit 3 shutdown.
Even if 10 kcfs outflows began today, it would likely take until Sept. 3 to bring the reservoir level down to 1,535, according to Corps estimates. At flows of 8.5 kcfs, which would be expected to bring TDG up to 115 percent below Dworshak, that reservoir level could likely be reached by Sept. 5.
The status quo operation or something like it would leave more water in Dworshak for later in September, when the peak of the fall chinook should be reaching the lower Snake, according to the Corps’ Doug Baus. The 2014 adult Snake River fall chinook return is expected to be a record.
And the Corps said Wednesday during a meeting of the TMT that the current spill level has already pushed TDG below the dam near to the 110 percent limit imposed by state of Idaho.
The NOAA Fisheries BiOp also says that dam operations must abide by state water quality rules.
Current DWR operational data may be found on the following website:
The Lower Granite adult trap was shut down both Tuesday and Wednesday when water temperatures reached 70 degrees for fear of harming fish through handling that are already being stressed. Temperatures above 68 degrees are judged to be unhealthy for the fish.
The SOR says the decrease in cool water discharge from Dworshak has several effects:
-- It will reduce the amount of cooler water entering Lower Granite’s reservoir and likely decrease the pool of cool water in the forebay. “This cool water pool provides refuge for both juvenile and adult salmon. Emergency pumps have been installed in the forebay to tap into the cool water at 20 meters depth and provide water to the adult ladder and trap at Lower Granite Dam.” Those emergency pumps provide about 25 percent of the water feeding the fish ladder. Other inputs come from higher level, warmer water.
Successful operation of the trap is a priority of many fisheries agencies. Maintaining emergency rental pump access to the cool water in the forebay is essential for effective operation of the trap and fish ladder.
“We’ve got a real-time issue here,” said NOAA Fisheries’ Paul Wagner. “Having it back to 10 kcfs would be desirable.” The fear is that at lower flows and, perhaps, hotter weather, the temperatures of the various flows into the ladder will rise, which could also potentially stall migrations.
-- “The reduction in Dworshak outflow results in up to 3 kcfs reduction in flow in the Lower Snake River which serves as a migration corridor for both juveniles and adults,” the SOR says.
-- “The reduction in flow in the lower Snake River reduces the level of spill at the lower Snake River projects when the projects are operating at minimum generation. Several of the Snake River projects operate a single turbine unit and spill all additional water. Thus a reduction in flow translates into a direct reduction in spill at these projects.”
“There are limitations to the level of TDG that would be acceptable. The Dworshak hatchery relies on the North Fork Clearwater for much of its water supply,” according to the SOR. The hatchery is just downstream of Dworshak Dam.
“Conversations with the hatchery manager indicate that TDG in the North Fork Clearwater in the range of 115 percent would likely be manageable. Real-time coordination with the hatchery managers will occur to ensure TDG levels are maintained within an acceptable range.”
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