Water budget for Lake Auburn, Maine, May 1, 2000 through April 30, 2003

Annual water budgets were developed for Lake Auburn in southwestern Maine for three water-budget years, May 1, 2000 through April 30, 2003. The measured inflow components of the water budget are direct precipitation to the surface of the lake and surface-water inflow. Mean annual inflow (precipitation
and surface water) to Lake Auburn during water-budget years 2001-03 was 816 million cubic feet. The measured outflow components of the water budget are evaporation from the surface of the lake, municipal water-supply withdrawals by the Auburn and Lewiston Water Districts, and surface-water outflow. Mean annual outflow (evaporation, withdrawals, and surface water) during water-budget years 2001-03 was 834 million cubic feet. The two largest components of the water budget are the surface-water inflow and municipal withdrawals. Surface-water inflow was about 62 percent of the mean annual inflow budget and municipal withdrawals were about 47 percent of the mean annual outflow budget. Changes in lake storage also were included in the water budget.

Dry conditions were present in Maine from 1999 to 2002, with a severe drought occurring in 2001 and 2002. On February 20, 2002, Auburn Water District recorded Lake Auburn?s lowest recorded water level, 256.7 ft, during the period of record from April 1, 1940 to June 20, 2003.

The total inflow and outflow volumes, adjusted for changes in lake storage, nearly balance for each water year. Any non-zero remainder volume for a given water-budget year is the residual. The mean annual residual for the three water-budget years is -1.06 million cubic feet (-7.93 million gallons). The changing sign of the computed residual from water-budget year to water-budget year during the 3-year study period indicates that no systematic errors were made in estimating inflows to or outflows from Lake Auburn. Because ground-water flow is unaccounted for in this water budget, any net ground-water flow is assumed to be contained in the residual term.