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Water Supply Forecasts Still Going Up; Now Ninth Highest Since 1960, Lower Granite Twelfth Highest
Posted on Friday, June 02, 2017 (PST)

The forecast for water supply in the Columbia River basin is continuing to rise ever so slightly, according to information provided at this week’s interagency Technical Management Team.


The April to August water supply forecast at The Dalles Dam rose to 113.472 million acre feet, higher than an early May estimate of 111.123 MAF. The new forecast ranks as ninth highest forecast for this time of year since 1960 and is 130 percent of the 30-year normal (1981 – 2010), according to Doug Baus of the U.S. Army Corps of Engineers. The earlier forecast released May 4, was 127 percent of normal.


The Dalles water supply forecast is at NOAA’s Northwest River Forecast Center’s website at Rankings for The Dalles water supply is at


Flows at the dam have been consistently above 400,000 cubic feet per second the last few days, Baus said. He expects that to peak by June 5 above 450 kcfs and drop back to 400 kcfs by June 9 (see


As of May 30, flow at The Dalles was 410.8 kcfs, with 227.9 kcfs of that as spill, creating a 24-hour total dissolved gas level in the tailwater of the dam of 122.8 percent. The Environmental Protection Agency has set an allowable TDG limit of 120 percent, but recorded TDG at Columbia and Snake river dams has consistently exceeded that limit due to the year’s high flows and spill.


Water supply at Lower Granite Dam, the upstream of the four lower Snake River dams, dropped slightly to 28.310 MAF, April to July, 143 percent of normal. That ranks as twelfth highest since 1960. The early May forecast was 29.118 MAF, 147 percent of normal.


Flow has also been consistently high through the Snake River dam projects, according to Baus, who said that flow at Lower Granite will rise to about 180 kcfs by June 3 and then drop to just over 140 kcfs by June 9 (


As of May 30, flow at Lower Granite was 148.4 kcfs, with 58.4 kcfs of that as spill, creating a 24-hour TDG level in the dam’s tailwater of 122.1 percent (


The Lower Granite water supply forecast is at Rankings are at


For more detail of the early May water supply forecasts across the Northwest, see CBB, May 12, 2017, “Heading Into Summer Water Supply Forecasts Across Columbia Basin Above Normal; Once Of Wettest Years,”


The entire Northwest will continue to be warmer than average with below average precipitation over the next 6 to 10 days, according to NOAA climate forecasts (, and the same forecast holds out to 14 days.


“Flows will continue to be high,” Baus concluded.


“How quickly things have changed this year,” said Russ Kiefer with the Idaho Department of Fish and Game in Boise. “Just going back to the third week in January, we had a below average water supply forecast. But the Boise River has been above flood stage since mid-February and it is still slightly above flood stage now.”


Further downriver, flow at Bonneville Dam as of May 30 was 426 kcfs. Some 238 kcfs is from spill, creating TDG of 120.1 percent.


Also see:


--CBB, May 19, 2017, “Climate Scientists Explain Ins And Outs Of Idaho’s Wild Winter This Season; No Drought Areas In NW,”


--CBB, April 14, 2017, “Big Water Mainstem: Runoff Supply Forecasts Continue To Rise At Columbia, Snake River Dams,”


--CBB, April 7, 2017, “2017 Runoff: Central Idaho’s Deadwood Summit gets 147 Inches Snow; Sees Five Times Above Normal,”

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