GSFLOW -- INTEGRATION OF THE USGS PRECIPITATION-RUNOFF MODELING SYSTEM (PRMS) WITH THE MODULAR GROUNDWATER FLOW MODEL (MODFLOW)

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Informed decisions about water resources require insight about the redistribution and utilization of changing environmental and social factors which strain and are in large part controlled by water availability. These decisions must take into account shifting factors such as climate change, natural disasters, and land-use which affect recharge, streamflow, water-quality, and plant and animal populations. The increasing range and complexity of these environmental resource management issues and policy development for natural and engineered systems requires an interdisciplinary and adaptive approach that builds on existing science and technology, is easily extensible and provides mechanisms for modeling over different temporal and spatial scales.

Dr. Ven Te Chow wrote in the preface of his classic book--Open-Channel Hydraulics, “In a science that has reached so advanced a state of development, a large portion of the work is necessarily one of coordination of existing contributions.” While this statement was made in the context of discussing open-channel hydraulics 51 years ago it holds true for interdisciplinary integration of hydrologic modeling and management objectives.

The coupled ground-water/surface-water model, GSFLOW, was written to work within the modular programming structures the U.S. Geological Survey (USGS) MODFLOW groundwater and Precipitation-Runoff Modeling System (PRMS) models. Existing and future MODFLOW packages and PRMS modules can be easily incorporated into GSFLOW. While the main reason for developing GSFLOW was to build a tool to quantify and predict spatial and temporal variability of interdependent surface and subsurface hydrologic fluxes of recharge, storage, and streamflow, its extensible programming structure allows for integration with models from other scientific disciplines. GSFLOW provides a means for integrating atmospheric, hydrogeologic, geographic, and computer sciences for modeling the full water cycle and associated processes of small watersheds to regional basins using global, regional, and local measured and projected data.