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)

Applications

VL- GSFlow can be used in a cell-based mode to calculate groundwater recharge on a daily or long-term average basis with full coupling and feedback from the groundwater flow system as represented in MODFLOW.  This integrated coupling allows the full hydrologic cycle to be simulated and a better understanding of groundwater/surface water interaction can be obtained.  Possbile applications include:

• Watershed-based hydrologic/water budget analysis
• Assessment of impacts of proposed development on surface and groundwater resources (LID)
• Surface-groundwater interaction modelling and distributed water budget modelling (for Source Water Protection)
• Analysis of changes to the water balance due to severe  drought and climate change
• Analysis of reforestation
• Baseflow analysis and characterization
• Transient and steady-state groundwater flow modelling

VL-GSFlow Interface

The VL-GSFLOW Pre– and Post Processor builds on the MODFLOW Management Module integrated into the VIEWLOG Borehole GIS System.  VIEWLOG provides complete access to the relational database, as well as geologic modeling, mapping, cross section and 3D visualization tools to support the model development process.

This module addresses the modelling process from a new perspective: A data-driven approach.  Today’s modellers need database, mapping, gridding and contouring tools that are not simply targeted at a single model simulation.  Complex model geometry, fine model grids and transient simulations demand a new level of data integration and management.