Application of an integrated surface water-groundwater model to multi-aquifers modeling in Choushui River alluvial fan, Taiwan

This research proposes a combination of SWAT and MODFLOW, MD-SWAT-MODFLOW, to address the multi-aquifers condition in Choushui River alluvial fan, Taiwan. The natural recharge and unidentified pumping/recharge are separately estimated. The model identifies the monthly pumping/recharge rates in multi-aquifers so that the daily streamflow can be simulated correctly. A multi-aquifers condition means a subsurface formation composed of at least the unconfined aquifer, the confined aquifer, and an in-between aquitard. In such a case, the variation of groundwater level is related to pumping/recharge activities in vertically adjacent aquifer and the river-aquifer interaction. Both factors in turn affect the streamflow performance. Results show that MD-SWAT-MODFLOW performs better than SWAT alone in terms of simulated streamflow, especially during low flow period, when pumping/recharge rates are properly estimated. A sensitivity analysis of individual parameter suggests that the vertical leakance may be the most sensitive among all investigated MODFLOW parameters in terms of the estimated pumping/recharge among aquifers, and the Latin-Hypercube-One-factor-At-a-Time sensitivity analysis indicates that the hydraulic conductivity of channel is the most sensitive to the model performance. It also points out the necessity to simultaneously estimate pumping/recharge rates in multi-aquifers. The estimated net pumping rate can be treated as a lower bound of the actual local pumping rate. As a whole, the model provides the spatio-temporal groundwater use, which gives the authorities insights to manage groundwater resources. Copyright (c) 2012 John Wiley & Sons, Ltd.