A ground-water flow model is being constructed for the Mississippi Embayment Regional Aquifer Study (MERAS) as part of the U.S. Geological Survey Ground-Water Resources Program’s effort to determine ground-water availability in multiple areas across the United States. The ground-water flow model input data will include: 2,700 geophysical logs for hydrogeologic framework development; 130 years of ground-water withdrawal information; 130,000 ground-water withdrawal locations; 39 rivers comprising 6,000 river miles; and precipitation, land use, surficial geology, and aquifer properties covering 70,000 square miles. Model calibration data includes 40,000 ground-water level observations and streamflows at 21 stream-gage locations.

In order to produce a ground-water flow model that can be modified for current or future needs, such as water level, solute transport, and optimization simulations, the MERAS model will be developed using the modular three-dimensional ground-water flow model code, MODFLOW-2005. The Multi-Node Well package will be used to simulate withdrawals from irrigation, municipal, and industrial wells, as some withdrawals occur from multiple aquifers. Major streams will be simulated using the Stream Flow Routing package of MODFLOW-2005, which allows simulation of flow through interconnected streams and flow to or from underlying aquifers. Additionally, the Local Grid Refinement capability of MODFLOW-2005 allows multiple, local models to be developed within larger, regional models.

Maintaining datasets in current digital formats constitutes an ongoing problem for many studies. An additional goal of the MERAS is to create datasets that will be usable for future model simulations such as the hydrogeologic framework dataset. Available geophysical logs will be scanned, top of the formation interpreted, and the log image and hydrogeologic digital surface made available on the web. Popularity and use of the framework and other model inputs in similar fashion may prompt the need to transform the datasets to future digital formats, therefore keeping the data readily available and current.