GSFLOW—A COUPLED GROUNDWATER/SURFACE-WATER FLOW MODEL FOR WATERSHED ANALYSIS

http://water.usgs.gov/nrp/gwsoftware/gsflow/gsflow.html.

Modeling environmental resource-management and policy issues requires an interdisciplinary and adaptive approach. Development of integrated models for these purposes has been hindered because individual models often have different spatial and temporal resolutions, use incompatible software and programming techniques, and lack feedback mechanisms to link the models. No existing model accounts for all environmental processes and interactions and each model and modeler produce differing results based on their different approaches and biases. A modeling structure is needed to facilitate integration of interdisciplinary scientific contributions.

To understand complex environmental resource issues integrated modeling of the hydrologic cycle is needed. As a step towards addressing integrated modeling, the Geological Survey (USGS) has developed the GSFLOW model; a coupled groundwater/surface-water flow model. It is an integration of the USGS Precipitation-Runoff Modeling System (PRMS) and Modular Groundwater Flow Model (MODFLOW). GSFLOW uses climate, solar radiation, topography, geology, land-use, and pumping data to simulate the temporal and spatial distribution of evapotranspiration, infiltration, surface runoff, snowpack and melt, interflow, recharge, streamflow, lake mechanics, unsaturated and saturated groundwater flow, and groundwater/surface-water interactions.

The extensible design of GSFLOW allows for inclusion of new solution techniques, which provides modelers with a structure to integrate additional models. It also allows for ease of comparison between alternative model components for a given process as their algorithms can be tested and compared, which can lead to improvements and better understanding of interactions, feedbacks, and sensitivities in a hydrologic system.

Future enhancements to GSFLOW include enhanced ability to simulate the effects of climate-change, water quality, conjunctive use and river system management, full-hydrodynamic streamflow with fate and transport of constituents.