Estimation of the effective precipitation recharge coefficient in an unconfined aquifer using stochastic analysis

Effectively managing groundwater relies heavily on estimating the amount of precipitation that may infiltrate the subsurface and supply groundwater. I n this study, we present a novel estimation method based on a stochastic ap proach to evaluate the quantity of precipitation that may recharge groundwa ter. The precipitation recharge coefficient is also investigated based on a n unconfined aquifer with an unbound, infinitely extended boundary conditio n. Moreover, a spectrum's relationship to the precipitation and groundwater level variation is also derived. The precipitation recharge coefficient ca n be obtained from the solution of the spectrum equation. Furthermore, sens itivity analysis is performed in order to determine the key Variable on the precipitation recharge coefficient. Analysis results indicate that the loc ation of an observation well affects the estimated precipitation recharge c oefficient. If the precipitation recharge area is large enough, the precipi tation recharge coefficient becomes insensitive to the location of the obse rvation well. The spectrum's relationship between the precipitation recharg e and groundwater level variation is also applied when estimating the preci pitation recharge coefficient upstream of the Cho-Shui River alluvial fan. According to those results, the precipitation recharge coefficient is 0.03 and the amount of groundwater recharge from precipitation is 35 million ton s of water annually upstream of the Cho-Shui River alluvial fan. Copyright (C) 2000 John Wiley & Sons, Ltd.