Salmon and hydro managers decided Wednesday to increase the flow of cooling water from Dworshak Dam's reservoir for three days in anticipation of what could well be the last heat wave of the season in the southeast Washington/west-central Idaho region.
The goal of the operation is to manipulate summer flows from the reservoir's depths in such a way as to hold temperatures downstream at the lower Snake River's Lower Granite Dam below 68 degrees F. Dworshak is located on the North Fork of the Clearwater River, which flows into the Clearwater and shortly thereafter into the lower Snake near the upper end of Lower Granite's reservoir.
Temperatures above 68 degrees can be unhealthy for coldwater fish such as salmon and steelhead who are swimming to and from the Pacific Ocean.
So far so good. The dam's tailwater temperature for the three days ending Thursday hovered 67 degrees, plus or minus a tenth or a degree or two, and at no time this summer has the temperature risen above 68.
As of this morning (Friday), 46.1 degree water from the North Fork was crashing into 76.6 degree water in the Clearwater, as monitored at Orofino, Idaho just above the confluence. That water then joins the Snake, which was at 73.1 degrees, as measured at Anatone just upstream of that confluence and downstream of the Hells Canyon Complex of dams on the Idaho-Oregon border.
During a Wednesday meeting of the Technical Management Team, NOAA Fisheries' Paul Wagner said that the Fish Passage Advisory Committee recommended that outflows from Dworshak be increased from about 12,000 cubic feet per second to 13.5 kcfs.
FPAC is a technical advisory group made up of federal, state and tribal members. TMT is made up of federal, state and tribal fish and hydro managers and is charged with adjusting hydro operations with the aim of improving survival of salmon and steelhead stocks that are listed under the Endangered Species Act. There are 13 such stocks in the Columbia-Snake river basin, including four in the Snake drainage.
The forecast is for air temperatures at Lewiston in the 95 to 98 degree range through the weekend and then some cooling is expected, Wagner said. More hot weather is possible, but becomes less likely with each passing day.
The TMT discussed when to turn down the Dworshak spigot -- today, Saturday or possibly Monday. All parties eventually agreed to drop the outflows from about 13.5 kcfs to "full powerhouse" flows at the end of the day Friday to conserve as much water as possible for the rest of the season. The powerhouse capability now is about 9.7 kcfs but increases as the reservoir level drops to as high as 10.5 kcfs.
The 2008 Federal Columbia River Power System biological opinion calls for a drawdown of the reservoir from full pool, 1,600 feet elevation, during the summer to 1,535 by Sept. 1, and then to 1,520 by the end of September. The BiOp offers prescriptions for improving the survival of listed salmon and steelhead.
The reservoir elevation dropped from 1,592 feet on July 15 when outflows were first increased to above full powerhouse to 1,566 by Friday morning, Aug. 6. The elevation has dropped by nearly three feet since outflows were increased Wednesday.
The keys now are the weather -- air temperatures and precipitation. If the weather heats up again and stronger Dworshak outflows are required, the cache of available water would be greatly reduced and would likely require later reductions to below full powerhouse, the Corps' Steve Hall said. Increased inflows would be helpful, but August is a month that typically yields little precipitation.