Introduction

Abstract

The applications of MODFLOW a modular three-dimensional finite-difference groundwater model of the U. S. Geological Survey, to the description and prediction of the behavior of groundwater systems have increased significantly over the last few years. The “original” version of MODFLOW-88 (McDonald and Harbaugh 1988) or MODFLOW-96 (Harbaugh and McDonald 1996a, 1996b) can simulate the effects of wells, rivers, drains, head-dependent boundaries, recharge and evapotranspiration. Since the publication of MODFLOW various codes have been developed by numerous investigators. These codes are called packages, models or sometimes simply programs. Packages are integrated with MODFLOW, each package deals with a specific feature of the hydrologic system to be simulated, such as wells, recharge or river. Models or programs can be standalone codes or can be integrated with MODFLOW. A stand-alone model or program communicates with MODFLOW through data files. The advective transport model PMPATH (Chiang and Kinzelbach 1994, 1998), the solute transport model MT3D (Zheng, 1990), MT3DMS (Zheng and Wang 1998) and the parameter estimation programs PEST (Doherty et al. 1994) and UCODE (Poeter and Hill 1998) use this approach. The solute transport model MOC3D (Konikow et al. 1996) and the inverse model MODFLOWP (Hill 1992) are integrated with MODFLOW. Both codes use MODFLOW as a function for calculating flow fields.