AHSAHKA, Idaho -- Continued rising temperatures forecasted for the coming week https://www.weather.gov have prompted changes in flow operations at the U.S. Army Corps of Engineers’ Dworshak Dam and Reservoir near Orofino, Idaho.
Water currently discharging at 9,500 cubic feet per second (cfs) from Dworshak Dam will increase at 12:01 a.m. on Thursday, July 11, reaching target flows of 12,500 cfs by early morning, according to U.S. Army Corps of Engineers (Corps) water-management officials. Downstream of the dam, water elevation will likely result in Clearwater River surface elevation increasing by about 9 inches at the at USGS gage located at Peck, Idaho.
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.
Total dissolved gasses (TDG) are expected are expected to remain below 110% and will be closely monitored. 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’ Walla Walla District reservoir managers are required to maintain water temperatures at Lower Granite below 68 degrees, if possible, using available reservoir-system management methods. 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. Reservoir managers must plan well ahead and make adjustments to water releases from Dworshak that will be effective at the time they will be needed further down the river.
Early this morning, July 10, Snake River temperature on the downstream side of Lower Granite was 66.8 degrees.
“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,” said Johnathan Roberts, a Walla Walla District reservoir regulator. “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.
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.
• 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., offering guided public tours of the dam at 10 a.m. and 1 p.m. The center also offers a variety of interpretive displays and movies about Dworshak and the history of the Clearwater River area, including the popular “Last of the Log Drives.”
For more information regarding water levels, facilities access or recreation, call the visitor center at (208) 476-1255, check out Dworshak Dam’s Facebook page at www.facebook.com/dworshakdam, or stop by the Visitor Center. Recorded-message water level and recreation information is also available by calling 800-321-3198.