Ground-water recharge is estimated as the residual component of a monthly water budget calculated using soil characteristics and long-term average rainfall, streamflow, irrigation, and pan-evaporation data. The water-budget components of rainfall, direct runoff, evapotranspiration, and ground-water recharge are defined seasonally, through the use of monthly data, and spatially by land-use and geohydrologic areas, through the use of a geographic information system model.
The long-term average ground-water recharge for the Iao area was estimated for four scenarios using natural land-use, and using 1926-79, 1980-85, and 1986-95 land-use and irrigation data. The recharge rate for natural conditions is 34 million gallons per day, which is 34 percent of rainfall. The average annual ground-water recharge rate for 1926-79 conditions is 51 million gallons per day, which is 41 percent of the sum of rainfall and irrigation. The recharge rates for 1980-85 and 1986-95 conditions are 40 and 36 million gallons per day, which are 37 and 35 percent of rainfall plus irrigation, respectively.
Additional publication details
USGS Numbered Series
Water Budget for the Iao Area, Island of Maui, Hawaii