VL-GSFlow is a pre– and post-processor for the GSFlow distributed-parameter groundwater/surface water model. GSFlow, a well-documented, open-source model developed by the U.S. Geological Survey and first released in the spring of 2008. GSFlow integrates the USGS MODFLOW groundwater model and USGS PRMS surface water model to providing a fully integrated modeling system.

The VL-GSFlow modeling interface represents the result of a number of years of in-house Earthfx development in the area of integrated watershed and water budget modeling. Building on Earthfx’s extensive experience with MODFLOW, in 2004 Earthfx began work on an interface to a customized and fully distributed version of the PRMS model. Our extensive experience with the two core components of GSFlow makes Earthfx uniquely positioned to develop and release the VL-GSFlow interface.

VL-GSFlow uses daily climate data (precipitation, solar radiation, temperature) along with the physical characteristics of the watershed to calculate the interception, runoff, evapotranspiration, ground water infiltration, and baseflow components of the hydrologic cycle. The surface water components are fully integrated with the MODFLOW representation of the saturated and unsaturated groundwater flow system.

Earthfx has adapted and expanded the USGS GSFlow code to include:
• Spatially distributed (cell-based) infiltration simulations. Studies have been done using 10 and 25 m cell sizes to better represent land use variation.
• Alternative SCS-curve number algorithm for estimating runoff
• Custom pre-processing tools for data preparation, climate data infill and baseflow separation.
• Custom calibration and post-processing tools that allow detailed analysis of temporal model results at any point within the watershed.
• Support for Windows x64 extended memory (>2GB memory limit)