River Managers Adjustingby CBB Staff
With hotter than normal weather and rising tailwater temperatures at Lower Granite Dam, the Technical Management Team increased the amount of water released from Dworshak Dam on Friday, July 23.
This week, as air temperatures declined from the 100 degree Fahrenheit mark, TMT agreed Monday, July 26, to drop flows from Dworshak Dam, but to release water at a lower temperature.
TMT increases or decreases flows in the summer from Dworshak Dam, located on the North Fork of the Clearwater River, as a way to govern water temperatures in the lower Snake River. In addition, TMT has the option to release water from the reservoir at various temperatures, which is another way to control tailwater temperatures at Lower Granite Dam downstream. Washington water temperature standards at Lower Granite Dam require the U.S. Army Corps of Engineers to keep tailwater temperatures at or below 20 degrees Centigrade (68 Fahrenheit).
Reacting to expected high air temperatures in the lower Snake River, TMT on Friday increased flows from Dworshak Dam by 2,000 cubic feet per second, from 11,600 cubic feet per second to 13.6 kcfs. That increased spill at the dam from 2 kcfs to 4 kcfs (powerhouse capacity is about 9.6 kcfs).
"TMT on Friday agreed to increase flows by 2000 (cfs) to get a larger volume of cold water down into the system for the weekend," said Rudd Turner of the Corps. "And, we also agreed to monitor river temperatures over the weekend. By Monday the temperature had not exceeded 68 degrees and with cooler (air) temperatures this week we lowered Dworshak outflows."
The current outflow at the dam is 11.6 kcfs, which includes spilling 2 kcfs of water. The drop in flows will conserve water for later in the summer when cold Dworshak water may be needed, according to TMT notes.
Salmon managers also requested lower release temperatures at the dam this week. While operators at the Dworshak National Fish Hatchery, operated by the U.S. Fish and Wildlife Service, prefer water temperatures to be 45 degrees this time of year, the operators agreed to the colder water through this week. The Corps, along with NOAA Fisheries and U.S. Fish and Wildlife Service, will consider increasing the outflow temperature to 45 degrees this Friday, July 30.
Turner said that water temperatures lower than 45 degrees affects how steelhead smolts feed and so will affect growth. "They get sluggish and 'go off feed and that slows growth," he said.
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