AHSAHKA, Idaho --
As the cool weather continues through today, we will start to see a significant warm up to the Clearwater and Middle and Lower Snake Basins starting on Sunday, July 21 and persisting through the early part of next week https://www.weather.gov. Temperatures are forecasted to be in the high 90s with the potential to hit 100 degrees in numerous locations on Monday, July 23, 2019.
Dworshak Dam began adding additional cool water to the river system Thursday, July 18, so that it will arrive at Lower Granite in time to help offset the warm temperatures as they begin to increase on Sunday, U.S. Army Corps of Engineers officials announce today.
“Current modeling and extend forecast show a reduction in temperatures after Tuesday and therefore we will begin to gradually reduce spill,” according to Jonathan Roberts, a Walla Walla District reservoir regulator.
Water is currently discharging at 12,500 cubic feet per second (cfs) from Dworshak Dam and will decreased over the weekend to 11,500 cfs. The flow change will gradually decrease the stage at United States Geological Survey (USGS) gage at Peck by approximately 6 inches over the next two days.
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) has been below 110% and is expected to decrease once the spilling has stopped. It remained under 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.
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.