Assessing Water Resources Using a New Hydrologic Model

GSFLOW is a new U.S. Geological Survey model for simulating ground-water/surface-water interactions. GSFLOW couples PRMS (the Precipitation Runoff Modeling System) to MODFLOW (the Modular Ground-Water Model) with modules for simulating flow and storage in unsaturated-zones, lakes, and streams. GSFLOW simulates infiltration, runoff generation, and lateral flow in temporarily saturated material (i.e., interflow beneath storm-generated perched water tables) with physically based equations. Unsaturated-zone flow beneath the soil zone is based on a 1-d kinematic-wave approximation to the Richards’ equation, implicitly coupled to MODFLOW. GSFLOW simulates spatialand time-varying ground-water recharge on the basis of daily energy and mass balances among precipitation, solar radiation, heat, evapotranspiration, runoff, infiltration, and storage in the snowpack and soil zone, and percolation and storage through the unsaturated zone as well as changes to recharge caused by ground-water pumping and surface-water diversions. The water resources of multiple basins in the United States and Australia are being evaluated with GSFLOW. The model will be used to relate physical and hydrologic characteristics of the basins such as land use, geography, and climate to water resources issues such as sustainable yield and surface-water/ground-water interaction. Application of GSFLOW in three dissimilar basins will provide a robust means of testing the new model and could provide new insights when assessing water-resources across the world.