Groundwater availability of the Coastal Lowlands aquifer system - refinement of a regional-numerical model

Author(s): Clark, B.; Duncan, L.; Foster, L.; Kress, W.

The Coastal Lowlands Aquifer System (CLAS), a large, regional aquifer comprised of multiple hydrogeologic units, is located along the Gulf of Mexico from the Texas/Mexico border through the Florida panhandle. Groundwater withdrawals from the aquifer system are primarily for public supply, irrigation, and self-supplied industry. As withdrawals from the system have increased, some areas along the Gulf have experienced water-level declines, saltwater encroachment, and land subsidence. The U.S. Geological Survey (USGS), as part of the Water Availability and Use Program, is developing a regional groundwater-flow model (~99,000 square miles) to simulate past, present, and projected conditions and to improve understanding of groundwater availability in the CLAS. The model incorporates a refined hydrogeologic framework, as well as improved estimates of aquifer recharge, water use, and groundwater-surface water exchange.

The refined hydrogeologic framework builds on work from the 1980s and 1990s for the USGS Gulf Coast Regional Aquifer System Analysis, and our agency is working with other locate, state, and Federal agencies to integrate data and knowledge gained since the original model was created. Improved land-surface-altitude data and methods to estimate recharge, additional driller’s log information, and data extracted from multiple smaller-scale models are a few of the sources for new information. After incorporation of these data and other model parameters, initial estimates of uncertainty will be calculated to help guide additional model refinement as an iterative process. The resultant model (or model ensemble) will quantify groundwater resources in the system and provide uncertainty ranges to better evaluate the predictive capability of future simulations.

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