Determination of evaporation and seepage losses, Upper Lake Mary near Flagstaff, Arizona

Two mass-transfer equations were developed to compute evaporation as a part of the evaporation were seepage-loss study for the Upper Lake Mary Reservoir near Flagstaff, Arizona, which has a capacity of 15,620 acre-feet and a surface area of 876 acres. The mass-transfer equations do not require an independent measure of evaporation to define the mass-transfer coefficient. Data from other evaporation studies were used to define the mass-transfer coefficient as a function of wind shear and atmospheric stability. Long-term seepage losses were determined by use of a seepage-probability curve-derived from a stage-seepage relation and defined by several selected short-term water budgets-and a lake-stage probability curve. Seepage curves were derived for several different amounts of assumed reservoir sealing. The long-term water saving that would result from each increment of lake-bottom sealing were computed. The study revealed that the evaporation loss was 27 percent of 2 ,100 acre-feet per year of the total reservoir inflow during 1950-71; seepage loss was 45 percent or 3,500 acre-feet per year. (USGS)