An areal recharge and discharge simulating method for MODFLOW

As a widely used groundwater flow model, MODFLOW offers a set of packages to simulate hydrologic stresses, inflows and outflows, to a groundwater system. Specifically, MODFLOW lacks a general method to process areally distributed recharge and discharge to groundwater. One solution would be to create a new package for MODFLOW. Alternatively, it is also possible to make the best use of existing code to the same effect. In this note, a simple, yet effective method to simulate areal recharge and discharge is proposed based on the recharge (RCH) package of MODFLOW, allowing multiple instances of the RCH package to be used in one model. The method has been implemented in MODFLOW2000/2005 and has been successfully applied to a regional groundwater flow model to simulate areally distributed precipitation recharge, agricultural discharge and irrigation infiltration recharge in a simple approach.