North Platte River flows into Lake McConaughy have fallen to lows similar to last decade's drought years.
But referring to “drought conditions'' when McConaughy experiences low inflows may no longer be accurate, said Mike Drain, natural resources manager for the Central Nebraska Public Power and Irrigation District.
“It may very well be a ‘new normal' inflow condition that we're going to have to deal with on a more frequent basis,” he said Monday.
Normally, Lake McConaughy's water supply is tied to return flows from the previous year's snowmelt runoff. In other words, snow that fell during the winter and spring of 2010-11 melts and runs off to be stored in U.S. Bureau of Reclamation reservoirs in Wyoming.
The water then is released for hydropower generation and irrigation projects in eastern Wyoming and western Nebraska. Water that enters the underground water system and flows back to the North Platte River — return flows — makes up most of the water available for storage in Lake McConaughy.
Over the years, a fundamental change has occurred in the timing and amount of water available for storage in McConaughy, said Cory Steinke, Central's civil engineer in charge of water operations.
Last year's record inflows were an exception to a developing trend of significantly lower flows, he said.
Steinke said many factors influence return flows to the North Platte River, including more groundwater development in the Nebraska Panhandle and improving irrigation efficiencies above McConaughy. The bottom line, he said, is that average annual inflows to McConaughy have been declining for several years.
“We can't rely on the occasional high-flow years for the reservoir to remain at healthy levels,” he said. “We're in decent shape now, but future reservoir levels are much more uncertain.”
Drain's and Steinke's remarks came during a meeting of Central's board in Holdrege, Neb.
Steinke summarized the current water supply situation as “not much snow, warm temperatures and early snowmelt.”
McConaughy's level is slowly falling as releases to satisfy downstream irrigation requirements exceed inflows. Recent inflows have been about 500 cubic feet per second, or 42 percent of the historic average. Outflows from Kingsley Dam have been around 800 cfs.
Lake McConaughy was 82.4 percent full Monday, or down 10.8 feet from maximum elevation.
Steinke said higher inflows this spring should have resulted from the tremendous amount of water that came down the North Platte River last year.
Though last year's snowpack was well above normal, this year's snowpack accumulation in the upper North Platte Basin is 38 percent of normal for this time of year, and 18 percent of normal in the lower basin. Snowfall accumulation this year all but ended in mid-March.
It typically continues to accumulate through mid-April.
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