U.S. GEOLOGICAL SURVEY GROUNDWATER TOOLBOX: A NEW GRAPHICAL AND MAPPING INTERFACE FOR ANALYSIS OF HYDROLOGIC DATA TO SUPPORT BASIN-SCALE UNDERSTANDING OF GROUNDWATER/SURFACE-WATER EXCHANGE

Basin-scale groundwater/surface water exchange provides context for any local-scale research, and a variety of computer techniques for hydrograph separation have provided that context for decades. These techniques use streamflow records to estimate groundwater discharge (base flow), surface-runoff components of streamflow, and groundwater recharge. Most of these tools are empirical; thus, it is prudent to interpret their results using an ensemble approach. Such an approach has been difficult in the past because individual codes must be run individually and their results compared manually. The U.S. Geological Survey (USGS) has developed a Groundwater Toolbox (GW Toolbox) computer program to facilitate execution and comparison of a variety of hydrograph separation methods.

GW Toolbox v1.0 includes six hydrograph-separation methods--the BFI (Standard and Modified), HYSEP (Fixed Interval, Sliding Interval, and Local Minimum), and PART methods; and one recession-curve displacement method--the RORA method to estimate groundwater recharge from streamflow data. The GW Toolbox is a customized interface built on the non-proprietary, open-source MapWindow geographic information system software. The program provides graphing, mapping, and analysis capabilities in a Microsoft Windows environment. In addition to the seven hydrograph-analysis techniques, the GW Toolbox facilitates retrieving time-series data (streamflow, groundwater levels, and precipitation) from the USGS National Water Information System, pre-processed GIS coverages, and meteorological data from the National Oceanic and Atmospheric Administration National Climatic Data Center. Data can be analyzed with several pre- and post-processing utilities. Using these tools, the GW Toolbox provides methods to estimate many of the components of the water budget for a hydrologic basin, including precipitation; streamflow; base flow; runoff; groundwater recharge; and total, groundwater, and near-surface evapotranspiration. Examples of GW Toolbox input and output and select applications of the hydrograph-analysis methods for basins across the United States demonstrate how the GW Toolbox can be used to efficiently apply a suite of hydrograph-analysis methods to better understand basin-scale groundwater/surface-water exchange.