Estimation of groundwater recharge using the soil moisture budget method and the base-flow model

Estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. The main purpose of this paper is to apply a water balance concept with two methods to estimate the groundwater recharge in the Ching-Shui watershed, Taiwan. First, a soil moisture budget method is established to estimate the infiltration, runoff, evapotranspiration, and groundwater recharge in the watershed, where the moisture content of the soil is tracked through time. Both soil-water properties of the unsaturated zone and climatic conditions must be fully considered. Second the base-flow model uses the base-flow separation from the total streamflow discharge to obtain a measure of groundwater recharge so that groundwater evapotranspiration is negligible. In contrast to the soil moisture budget method, base-flow estimation does not require complex hydrogeologic modeling and detailed knowledge of soil characteristics. In a previous study, we suggested that high base-flow is caused by rainstorm events. Using model analysis, depths of recharge estimated by stable-base-flow analysis are adopted to obtain more reasonable groundwater recharge values. The results indicate that assessment of the average annual recharge obtained with a soil moisture budget and the base-flow are very close; the ratio of the two methods is about 95.3%.