IMPLEMENTATION OF A DAILY SOIL WATER BALANCE MODEL FOR ESTIMATING SPATIAL AND TEMPORAL DISTRIBUTIONS OF AQUIFER RECHARGE

A simple, daily soile-water balance model was developed to estimate the spatial and temporal distribution of recharge for watersheds in humid regions (Dripps, 2003). The model was implemented using Visual Basic within Microsoft Excel; although this software architecture worked well for the original implementation, its computational performance is inadequate for regional-scale model development.

The author has reimplemented the original code in Fortran-95, using an object-based design. The new code provides a "pluggable" application programming interface (API) for the important processes (snow melt, overland flow routing, evapotranspiration, and soil-water balance). Model runs are configured using GIS coverages of ground elevation, land use, and soil properties, and other adjustable inputs based on the processes desired by the user. Currently, the code provides the simple snow-melt and overland-flow routing procedures used in the original model, four different evapotranspiration models, and two soil-water balance models. The code was developed under contract with USGS, and the code will be made publicly-available after review.

The author will describe the soil-water balance model, the design of the Fortran 95 code, and its application. Example applications will be provided, including the predicted spatial and temporal recharge distributions.