Using GIS for Development and Processing of Surface-Water Data for the TWDB GAM Models

By

JORDAN, DAVID L.

INTERA Incorporated, Albuquerque, NM

INTERA Incorporated is assisting the Texas Water Development Board (TWDB) with its Groundwater Availability Modeling (GAM) project. The focus of the GAM project is to provide a methodology to evaluate groundwater supplies over a 50-year planning horizon. The models that are being developed for the GAM project are quite large, typically encompassing tens of thousands of square miles. A very large volume of data must be acquired, processed, analyzed, and converted to MODFLOW input file format as part of the GAM project. In particular, information on a large number of streams must be processed into input data for the MODFLOW stream-routing package, which simulates both stream flow and stream-aquifer interaction. We have developed a variety of automated techniques for creating the MODFLOW stream-routing package input files from ArcView GIS data. These methods allow us a great deal of flexibility in adding or deleting streams from the model during model construction and calibration. We have developed an automated stream-segment numbering tool in ArcView that will number stream segments taken from EPA RF1 river reach data consistent with the MODFLOW stream-routing package. The utility also automatically determines connectivity between tributaries. We have also automated the numbering of reaches and assigning of reach numbers to the model grid. Using manual methods, stream segment and reach numbering could be very labor-intensive. However, these operations are greatly simplified and accelerated using automated techniques.