Applying a three-dimensional numerical model to evaluate the safe yield of groundwater in the mountainous midstream of Jhoushuei River Basin

The investigation of groundwater Sources in the alluvial plain is abundant in Taiwan. The mountainous region occupied 2/3 of Taiwan area, but the information of groundwater Sources in the mountainous region is very lack. In this study, groundwater modeling system (GMS) with MODFLOW code is used to evaluate the groundwater Sources in the midstream of Jhoushuei River Basin, Taiwan. A three-dimensional numerical model is used to evaluate the safe yield of groundwater under steady state situation. The safe yield is defined as the outflow from the specified head boundary in the west part of the study area and does not disturb the original groundwater system. The conceptual model is constructed first and then the numerical model is built based on the conceptual model. The numerical model is calibrated by the observed groundwater level. Mean precipitation data from 2000 to 2009 is input in the numerical model to evaluate the safe yield in the study area. The result shows that the mean safe yield is about 199×106 ton/year. The safe yield under the maximum and minimum precipitation situation is 201×106 and 198×106 ton/year, respectively. The influence of the input precipitation is not sensitive. This might be due to the reason that the mountain alluvia and river contain most of the water from precipitation in this area.