15-037 Dworshak discharge flows increased to cool rising river temperatures

Published June 17, 2015
AHSAHKA, Idaho – Low seasonal inflows, recent hot weather conditions and more of the same forecasted for the rest of the week have prompted changes in flow operations at Dworshak Dam and Reservoir near Orofino, Idaho.

Water previously discharging at 2,900 cubic feet per second (c.f.s.) from Dworshak Dam was increased late Tuesday night to 5,300 c.f.s., according to U.S. Army Corps of Engineers water-management officials.
Downstream of the dam, water elevation will likely result in Clearwater River elevation increasing by about 0.75 feet at the North Fork confluence.

The National Oceanic and Atmospheric Administration’s (NOAA) Columbia River System Biological Opinion (BiOp) requires the Corps to meet several objectives to enhance ESA-listed fish survival, 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 downriver to the ocean.

“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,” said Steve Hall, Walla Walla District Corps reservoir manager. “We are required to maintain water temperatures at Lower Granite below 68 degrees, if possible, using available reservoir-system management methods.”

Yesterday, Snake River temperature on the downstream side of Lower Granite was 67.3 degrees, said Hall.

“With such 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,” Hall said. “Dworshak’s 42-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, Hall added.

Dworshak Reservoir reached full-pool elevation on June 7, offering earlier-than-usual prime-water recreation conditions. Although gradually lowering, Dworshak Reservoir will likely be within 5-7 feet of full-pool during the upcoming Independence Day holiday weekend, based on reservoir modeling.

Natural Resources staff note having the reservoir a few feet down from full can actually be a good thing for visitors.

“Lake is full, full, full right now. This also means woody debris that is usually beached along the shoreline is floating around and making boating difficult,” explained Paul Pence, Dworshak’s natural resources manager. “When the pool drops down several feet, much of that debris stays on the shore and beaches become exposed at almost all of the shoreline camps. We like to see the lake full, but boating and shoreline camping is actually easier when the water is down a few feet.”

Dworshak natural resources staff invite visitors to camp, boat and play at Dworshak Reservoir:

• Daytime, surface water temperatures currently range between 72-78 degrees.
• Bass and kokanee fishing are plentiful.
• Shoreline campsites are open, clean and ready for use.
• Destination and safe-harbor docks have all been cleaned, repaired and/or replaced.
• Dent Campground is open and accepts reservations at www.recreation.gov.
• Dworshak State Park is also open https://parksandrecreation.idaho.gov/parks/dworshak.
• Life jacket loaner-boards are open and fully stocked. Please, use and return them.
• Dworshak Visitor Center is open daily, offering guided public tours of the dam at 9 a.m., 11:30 a.m., and 2:30 p.m.

Corps officials advise boaters and other people using waterways both in Dworshak Reservoir and below the dam on the Clearwater River to be alert to changes in water elevation and volume of flow. Current water-management conditions can be viewed on the District website at www.nww.usace.army.mil/Missions/WaterManagement.aspx.

Rangers encourage visitors to enjoy the reservoir safely, by taking the following precautions:

• When boating on the reservoir, please use caution because lake levels can change quickly – anchor your boat in water deep enough to avoid beaching and leave enough slack in your anchorline to avoid sinking should lake levels fluctuate up or down.
• Changing weather conditions can create unsafe situations on open water. Know the weather and have a float plan.
• Ensure properly fitting, accessible and serviceable life vests are available for each occupant on your boat. Better yet, wear them.
• Keep life jackets on children while on or around the water. Don’t let small children out of your sight.
• Check the serviceability of your boat.
• Before proceeding at higher speeds, familiarize yourself with the area you will be boating as there may be floating woody debris or rocks, stumps and shallow areas not visible from the surface.
• Water temperatures from outflows at Dworshak Dam are about 43 degrees -- be aware of hypothermia risk when wading or swimming in the North Fork and near the confluence of the Clearwater River.

The Dworshak Dam Visitor Center is open daily from 8:30 a.m. to 4:30 p.m. For more information about Dworshak recreation opportunities, call the visitor center at 208-476-1255. Follow Dworshak on Facebook to get the latest updates www.facebook.com/dworshakdam.

Public Affairs Office

Release no. 15-037