May, June Rains Raiseby Mike O'Bryant
Late May and early June rains raised the water supply forecasts in much of the Columbia River Basin, including at The Dalles, where the water supply rose from 74 percent of normal in May to 79 percent in June.
The Northwest River Forecast Center released a June final water supply forecast this week that reflects the sometimes-heavy rains that have fallen in the basin over the past three weeks. The only major area where the water supply didn't increase is the Kootenai River Basin, where the forecast dropped eight percentage points to 71 percent of normal.
Still, most water supply volume forecasts rose and that has allowed dam and fishery managers at the Technical Management Team to continue protection flows for juvenile steelhead migrants in the mid-Columbia River. The increased flows from Grand Coulee Dam, where the water supply forecast rose 1 percent from 52.2 million acre feet (maf) to 53 maf (January through July), will allow sufficient water for Grant County Public Utility District to maintain flows at its Priest Rapids Dam of 125,000 to 135,000 cubic feet per second.
TMT first set that flow June 1, recognizing the operation might have to be adjusted downward if the water supply did not improve. Refilling Lake Roosevelt by June 30 is a higher priority in the NOAA Fisheries 2000 Biological Opinion than is the higher river flow because the stored water will be needed to augment flows later in the summer. The elevation at Lake Roosevelt is 1,284 feet, eight feet from full.
Also on the rise is the forecast for Lower Granite Dam, which increased from 67 percent of normal (18.8 maf) to 71 percent of normal (21.1 maf), January through July. The April through July forecast at Lower Granite rose to 15.4 maf, which is 71 percent of normal.
The forecast for Dworshak Dam, an estimate made by the U.S. Army Corps of Engineers, rose from 3.05 maf in May to 3.3 maf in June, which is 87 percent of normal, a 9 percent rise. The Dworshak reservoir elevation is 1,593 feet this week, about seven feet from full.
On the downswing is Libby Dam, where the water supply dropped from 4.9 maf to 4.55 maf, which is 71 percent of normal. That's below the threshold of 4.8 maf that allows for sturgeon operation in the Kootenai River, said the Corps' Rudd Turner.
Flows from Libby Dam rose from 4 kcfs to 13 kcfs May 29 after two radio-tagged female Kootenai River white sturgeon quickly turned downstream in the river's Canyon reach. The sudden movement was a signal that the fish had completed spawning and that higher flows were needed to protect the gametes while they incubate, hatch, absorb the yolk sack and become free swimming. The Kootenai white sturgeon are listed under the federal Endangered Species Act as endangered.
If the sturgeon had spawned one week later after the water supply forecast had dropped below the 4.8 maf threshold, the operation may not have been available, according to the U.S. Fish and Wildlife Service biological opinion that guides the sturgeon's recovery, Turner said.
However, Bob Hallock of the USFWS said the intent of the BiOp was to use the May water supply forecast for the spawning that is expected yearly in late May or early June. "There's not logic to use the June forecast for a May operation," he said. He said the USFWS would clarify that in the next BiOp for the sturgeon.
Flows from Libby Dam are now at 14 kcfs and will rise to 15 kcfs June 13, and to 16 kcfs June 20 for one week before flows drop to a level designed to protect threatened bull trout in the river. TMT will determine what that flow level will be at its next meeting. Lake Koocanusa, which backs up behind Libby Dam, is at an elevation this week of 2436 feet, about 23 feet from full.
Technical Management Team: www.nwd-wc.usace.army.mil/TMT/index.html
Water Supply Forecast: www.nwrfc.noaa.gov/water_supply/ws_runoff.cgi
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