Expectations for rising runoff in the Columbia River basin to generate additional electricity sold by the Bonneville Power Administration is due to the lessening of El Nino conditions and the rise of La Nina, said Rick van der Zweep, a hydrologic forecaster with the U.S. Northwest River Forecast Center NWRFC.
"This year we are into a moderately strong La Nina and that tends to push more storms our direction," said van der Zweep.
Just recently, the NWRFC projected water runoff at the key Dalles Dam on the Columbia River at 101 percent of the 30-year normal for January through July, up from the previous forecast of 97 percent and well above 2010's actual runoff of 79 percent of normal.
The Bonneville Power Administration BPA said the agency "has been aware for some time that a combination of high streamflows and high wind could pose new challenges," in a letter issued to market participants in September.
Last summer, a short period of heavy rainfall forced BPA to curtail nuclear and wind generation so that it could increase its hydropower output to protect certain fish species.
Curtailing wind output could reduce generators' revenue from production tax credits and renewable energy credits and depress overall wholesale electric prices in the region.
BPA said it is working with the market on a draft to formalize its "environmental-redispatch" policy a last resort to be used when hydropower must be increased to replace other generation, BPA said.
"While we believe there are solutions that would keep all parties economically whole, this is a significant concern," BPA said in a letter last month.
BPA has about 3,000 megawatts of wind in its four-state control area and an additional 3,000 MW is expected to interconnect in the coming years.
The NWRFC's rising river forecast was in part due to mid-January rainfall that brought flooding to areas of western Washington and created early snow melt, said van der Zweep.
"This was a quite warm storm, a Pineapple Express, so the freezing levels went to well over 7,000 feet," he said. "We lost a lot of our low-elevation snow. Some runoff we thought would occur in the April-to-June period came off in January."
For the first half of the month, rain accumulation for the Columbia basin is running at 163 percent of normal, according to the NWRFC. Since the NWRFC's 2011 water "year" began October 1, the basin has received 116 percent of normal rainfall.
That compares with January 2010 when the Columbia basin's rainfall accumulation was 94 percent of normal and the total for the water year stood at just 87 percent.
Another forecasting service, Point Carbon, has projected that river runoff at the Dalles will be 107 percent of normal for the April-September period, even higher than the government agency's forecast.