WRRCTR No.151 Water Balance of the Pearl Harbor-Honolulu Basin, Hawaii, 1946-1975

Abstract

The basal aquifer underlying the Pearl Harbor-Honolulu Basin comprises the principal source of water supply for municipal demands of greater Honolulu and the demands of irrigated agriculture. Declining freshwater head and increasing chlorinity of coastal well water have led to recent groundwater development controls in the area. Determination of the sustainable (safe) yield of the basin requires a spatially and temporally detailed estimate of the recharge. The water balance of the basin was computed for 258 discrete zones at a monthly interval over the 1946 to 1975 (360 months) period. Results of the analysis include estimates of monthly precipitation, fog drip, sugarcane irrigation, urban lawn sprinkling', runoff, evapotranspiration, and groundwater recharge for each zone. The average recharge rate of the critical Pearl Harbor region was found to be 11.74 m^3 /s (268 mgd), of which 2.98 m^3 /s (68 mgd) is derived from the return of applied irrigation water. Results indicate that the groundwater resources of the basin are sufficient to support a population increase of approximately 450,000, should sugarcane and pineapple cultivation be discontinued.