Hydrology of Crater, East and Davis Lakes, Oregon by Kenneth N. Phillips
The water budget of Crater Lake includes income as infalling precipitation and inflow from the caldera walls and outgo as evaporation and seepage. For this study these budget items were determined in the following order: (1) Seepage loss was computed from changes in lake level during periods of no precipitation and little inflow in the period November 4, 1961, to April 18, 1962, (2) infalling precipitation was computed for periods of heavy snow or rainfall from October 10, 1961, to April 29, 1962, with adjustment for seepage and estimated peripheral runoff, and the results were compared with simultaneous records of precipitation at the weather station, (3) annual inflow (a small part of the total water supply) was estimated from runoff at gaging stations on the Rogue River, and (4) evaporation was assumed to account for the difference between total annual water supply and seepage loss, adjusted for any change in lake level.
The elements of the water budget are approximately as follows: Seepage loss ranges from about 86 cfs at a lake level of 6,163 feet to 101 cfs at a level of 6,179 feet; the long-term average loss is about 89 cfs. Infalling precipitation is about 7 percent greater than that observed at the weather station. The total water supply reaching the lake is about 1,386 acre-feet per inch of observed precipitation at the weather station. The average evaporation loss is about 23 inches per year from the lake surface. The lake level has been observed to range from a minimum of 6,163.2 feet on September 10, 1942, to a maximum of 6,179.06 feet (high-water mark of 1958).