The U.S. Army Corps of Engineers is working to keep total dissolved gas levels under 115 percent at Ice Harbor Dam on the Snake River, and water temperature below 68 degrees Fahrenheit at Lower Granite Dam.
The Columbia River Technical Management Team grappled with both issues on July 29.
At Ice Harbor, total dissolved gas exceeded the state standard of 115 percent on July 21, 22 and 23, with gas levels measured at 116 and 117 percent, the Corps reported. TMT decided July 24 to resolve the issue by adjusting spill at Lower Monumental Dam, upstream. The plan was to send spill through four bays instead of seven, including the spill bay with a removable spillway weir. But when spill exceeded 17 kcfs, the system automatically reverted to a uniform spill pattern, Corps representative Alexis Mills told the team. The Corps then reverted to its bulk spill pattern due to significant changes in TDG from testing that began July 27, she said.
At Lower Monumental on July 28 a cable holding a guide wall broke and the wall started moving toward the spillway, although it was still held by another cable. Operators shut off the removable spillway weir due to the emergency situation, the Corps' Chris Peery told the team. The agency was uncertain when repairs would be made. However, TDG levels dropped so the change in operations became unnecessary.
Dam operators at Dworshak Dam on the Clearwater River are working to ensure cooler water from the tributary is released to the Snake River to cool temperatures at Lower Granite Dam during the current heat wave.
Corps representative Jon Roberts told the team the agency has been sending about 9.5 kcfs through the powerhouse, and another 3 kcfs to 3.5 kcfs over the dam as spill to send as much cool water as possible to the Snake River without exceeding the 110 percent TDG standard. He said water temperatures so far have remained below 68 F—the threshold when warmer water begins to harm fish.
With extreme heat expected to continue through the weekend of Aug. 1-2, Roberts said the Corps would continue pushing cooler water through Dworshak.
Fish managers planned to receive more information about impacts on temperature before discussing further whether to ask dam operators to close the removable spillway weir at Lower Granite, and whether to save some cooler water held behind Dworshak for later in the summer.