Development and application of the integrated SWAT–MODFLOW model

This paper suggests a new approach for integrating the quasi-distributed watershed model, SWAT, with the fully-distributed ground-water model, MODFLOW. Since the SWAT model has semi-distributed features, its groundwater component does not consider distributed parameters such as hydraulic conductivity and storage coefficient. In generating a detailed representation of groundwater recharge, it is equally difficult to calculate the head distribution and the distributed pumping rate. In order to solve this problem a method is proposed whereby the characteristics of the hydrologic response units (HRUs) in the SWAT model are exchanged with cells in the MODFLOW model. By using this HRU–cell conversion interface, the distributed groundwater recharge rate and the groundwater evapotranspiration can be effectively simulated. By considering the interaction between the stream network and the aquifer to reflect boundary flow, the linkage is completed. For this purpose, the RIVER package in the MODFLOW model is used for river–aquifer interaction. This combined modeling is applied to the Musimcheon Basin in Korea. The application demonstrates that an integrated SWAT–MODFLOW is capable of simulating a spatio-temporal distribution of groundwater recharge rates, aquifer evapotranspiration and groundwater levels. It also enables an interaction between the saturated aquifer and channel reaches. This interaction played an important role in the generation of groundwater discharge in the basin, especially during the low flow period. The advanced water transfer method in SWAT–MODFLOW was successfully tested, and reproduced the distributed drawdown and reduced stream flow by pumping with multiple wells. Therefore, when considering discharge to streams, springs or marshes, the use of this model would be beneficial in planning for the sustainable development of groundwater.