Your PUD News Release

Updated Lake Chelan runoff estimate is 81 percent of average

Chelan County PUD
News Release
3/4/2010

Eighty-one percent of average runoff would result in 425,300 second-feet-day (SFD) or 843,400 acre-feet (A.F.) of water. Last year’s actual runoff from April 1 through July 31 was 427,051 SFD, which was 81 percent of average. Current long-range weather forecasts are calling for a slightly wetter and warmer-than- average March.               

Snowpack densities at Lyman Lake, Park Creek Ridge and Miners Ridge are all 36 percent. Average density for this time of year at these three sites is 36 percent. Precipitation in Stehekin from November through February was 18.7 inches, which was 84 percent of average, and 88 percent of last year’s accumulation at this time. Moisture content in the soil, also known as soil prime, is average.     

The elevation of Lake Chelan on March 1, 2010, was 1090.8 feet, which is 5.1 feet higher than the expected average under the current operating license, and 3.2 feet higher than last year. The elevation of Lake Chelan is significantly higher than the expected average because of 1) decreased powerhouse capacity due to modernization of powerhouse generating units and 2) above average precipitation in November 2009.

Generation will be managed this winter and spring with the intent of meeting all seven operating objectives in the Lake Chelan Hydro Operating License, as well as minimum lake elevation targets. The first minimum lake elevation target in 2010 is 1087.6 feet on May 1. Generation will likely be scheduled at maximum available capacity (which is less than average due to modernization efforts) through this winter and spring, unless future Chelan Basin runoff forecasts drop below approximately 80 percent of average.

The Northwest River Forecast Center’s (NWRFC) official runoff forecast (regression method), for January through July, is 77 percent of average at Grand Coulee Dam and 69 percent of average at The Dalles. Runoff forecasts for other local area basins are also below average. The NWRFC’s runoff forecast, for April through September, is 70 percent of average for the Wenatchee River and 68 percent  of average for the Okanogan River.

At right is a color coded diagram of the Western United States, which shows mountain snowpack in percent of average snow water equivalent. Note that snowpack in Central Washington basins range from 50 percent to 90 percent of average.