Don't tell folks familiar with Lake McConaughy that the drought is over.
Generous rainfall this spring pulled much of Nebraska out of persistent drought conditions, but the Panhandle and the North Platte River watershed above Lake McConaughy haven't been as fortunate, says Tim Anderson, public relations manager for the Central Nebraska Public Power and Irrigation District, based in Holdrege.
Nothing illustrates the lack of precipitation better than recent inflow data at Lake McConaughy, according to Anderson. Inflow measured at the Lewellen river gauge on June 25 was only 84 cubic feet per second, or 4.5 percent of the average June 25 measurement since storage began in 1941.
The lowest daily inflow ever recorded--38 cfs--occurred on June 24, 2002.
Drought has gripped the North Platte River watershed since 2000. Lack of snow in the Rocky Mountains of Wyoming, the primary source of Lake McConaughy's water supply, resulted in low runoff and inflows to federal reservoirs on the North Platte River that store water for irrigation in eastern Wyoming and western Nebraska. Most of the water that flows into Lake McConaughy comes as return flows from upstream surface water irrigation projects.
Rivers and streams already suffering from a lack of precipitation have also been affected by additional groundwater development. Wells that are hydrologically connected to surface water streams intercept groundwater that would otherwise move back to the stream, further lowering instream flows and inflows to Lake McConaughy, Anderson says.
During May and June--the time of year when stream flows are typically at their highest--inflows to Lake McConaughy averaged 388 cfs, or 22% of the May-June average of 1,780 cfs since 1941.
"We had projected the possibility that inflows to Lake McConaughy could fall to record lows this year," says Cory Steinke, civil engineer with The Central Nebraska Public Power and Irrigation District. "Below average snowfall in the mountains, long-range precipitation forecasts above the lake, stream flow trends over the past several years, and the impact of groundwater development on stream flows all pointed to the very real possibility that the bottom would fall out of inflows. Unfortunately, that's exactly what has happened."
On May 1, Lake McConaughy was four feet lower than it was on May 1, 2006. However, precipitation below the lake raised stream flows and enabled Central to delay releases for several weeks. As a result, the lake in early July was about three feet higher than it was at the same time last year. The lake's peak elevation this year was reached last week at 3,220.3 feet above mean sea level.
Precipitation in the Platte River valley also made it possible for Central to divert excess river flows into Elwood Reservoir, adding more than 15 feet to the lake's water level. Central received permission from the Nebraska Department of Natural Resources to divert water from the Platte into the reservoir over the course of several days in June when flows exceeded existing instream flow water rights and target flows established by the U.S. Fish and Wildlife Service.
"The precipitation in and around the irrigated area has been more than welcome," Steinke says, "but the inflow data at Lake McConaughy reminds us that water supplies are still well below normal."