RECHARGE STUDIES IN A SHALLOW SAND AQUIFER USING SWAT AND MODLFOW

An outlier of the Sparta Sand in southeastern Wood County, Texas was modeled using SWAT and MODFLOW to determine recharge rates and to make predictions for groundwater sustainability. In recent years groundwater sustainability has become an issue of increasing importance in Texas. The concept of sustainability depends heavily upon quantification of recharge. An outlier of the Sparta Sand was recently developed for groundwater production. Of concern to its developers is both long term sustainability of production and factors influencing recharge to the small aquifer. The outlier covers an area of about 5 square km and is an average of 30 m thick. Three types of groundcover are found within the recharge area: mixed pine and oak woodland, oak brush and grassland. The Soil Water Assessment Tool (SWAT) is a model used in the generation of water budgets, a component of which is deep percolation, which can be interpreted as recharge. Field and historic data for precipitation, soil moisture, water levels, pumping rates and spring/stream flow were used to produce deep percolation (recharge) values in SWAT. These recharge values were then used in the calibration of a MODFLOW simulation of the Sparta Sand outlier. After calibration, long term pumping schemes were simulated in MODFLOW to predict groundwater levels under various climatic and groundcover conditions by using SWAT generated recharge rates for woodland, brush and grassland cover types and historic climatic data for drought years. Results of this study should aid in managing groundwater in shallow sand aquifers in both East Texas and other areas where extended extraction may be planned.