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June Water Supply Forecasts For Columbia Basin Far Above Normal, Continue To Climb
Posted on Friday, June 09, 2017 (PST)

Forecasts for the summer’s water supply in the Columbia River basin continue to climb at many basin dams.


The April to August forecast at The Dalles Dam rose to 115.610 million acre feet, which is 132 percent of normal, said Doug Baus of the U.S. Army Corps of Engineers, at this week’s interagency Technical Management Team meeting.


Just one week ago, the April to August forecast, which is a product of the Northwest River Forecast Center, was 113.472 MAF, 130 percent of the 30-year normal (1981-2010). Both this week’s and last week’s forecast at The Dalles are adjusted from the May final forecast, which was 127 percent of normal.


Forecasts for The Dalles sets certain guidelines for other areas of the basin. The March final forecast sets Columbia River Water Management Plan adjustments for Grand Coulee Dam. The April final forecast sets spring flow objectives at McNary Dam. The May final sets end of September draft limits at Hungry Horse and Libby dams and the July final forecast sets the end of August draft limit at Grand Coulee Dam.


Daily average flow at The Dalles on June 7 was 405,400 cubic feet per second with 226 kcfs of that as spill. Flow and spill data is at


Daily average flow at Bonneville Dam on June 7 was 428.5 kcfs with 238.7 kcfs of that as spill.


The Lower Granite Dam on the lower Snake River April to July water supply forecast is 29.293 MAF, 148 percent of normal. That forecast is up from last week’s estimate of 28.310 MAF, 143 percent of normal. The early May forecast was 29.118 MAF, 147 percent of normal.


The June final at Lower Granite, provided by the NW River Forecast Center, sets the summer flow objective at the dam.


Daily average flow at Lower Granite on June 7 was 154.3 kcfs with 65 kcfs spill.


June forecasts for Hungry Horse Dam on the South Fork of the Flathead River in Montana, according to Mary Mellema of the U.S. Bureau of Reclamation, are: June to July, 1.040 MAF, 121 percent of normal; January to July, 2.698 MAF, 129 percent of normal; April to August, 2.326 MAF, 120 percent of normal; and May to September, 2.020 MAF, 119 percent of normal.


The April to August Hungry Horse forecast, provided by BOR, sets minimum flows at the dam and at Columbia Falls Dam. The May to September forecast sets VARQ refill flows at the dam.


The April to August forecast at Libby Dam on the Kootenai River in Montana dropped from 8.190 MAF to 7.594 MAF, 129 percent of normal. The May final April to August forecast sets minimum sturgeon flow volume and minimum bull trout flows, which occur after the sturgeon pulse and go through September. The June final sets VARQ refill flows at the dam.


Also see CBB, May 12, 2017, “River Managers To Boost Flows From Libby Dam To Aid Kootenai River White Sturgeon Spawning,”


The April to July Forecast for Dworshak Dam on the North Fork of the Clearwater River is 2.838 MAF, 116 percent of normal. Dworshak’s water supply is calculated by the U.S. Army Corps of Engineers.


Daily average flow at Dworshak on June 7 was 2.8 kcfs with no spill.


At Grand Coulee Dam the April to August forecast is 70.365 MAF, 124 percent of normal, and Albeni Falls Dam on the Pend Oreille River is 15.720 MAF, 127 percent of normal.


Daily average flow at Grand Coulee on June 7 was 213 kcfs. Spill was 0.6 kcfs.


Forecasts are at


Also see:


--CBB, June 2, 2017, “Water Supply Forecasts Still Going Up; Now Ninth Highest Since 1960, Lower Granite Twelfth Highest,”


--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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