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Lower Mississippi-Gulf Water Science Center -- Arkansas
Digital Hydrogeologic Surface and Thickness of the Mississippi Embayment Regional Aquifer Study (MERAS)
Short Title: MERAS Framework
Project Chief: Rheannon Hart
Cooperator: U.S. Geological Survey Office of Ground-Water Resources Program
Project Time Frame: January 2006 - 2009
A hydrogeologic framework for a ground-water flow model is under development as part of the U.S. Geological Survey (USGS) Ground-Water Resources Program to aid in determining ground-water availability in selected areas of the United States. The Mississippi Embayment Regional Aquifer Study (MERAS) encompasses about 70,000 mi2 and parts of eight states including Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. Over 2,750 geophysical logs were compiled for the study area in the Mississippi embayment to create digital surfaces of the principal geologic units from land surface to the top of the Midway confining unit of upper Paleocene age. Thickness maps were created for all the units for which tops and bases were determined. The digital surfaces and thickness maps were created to provide a framework for a regional ground-water flow model of the MERAS and to provide digital grids of the surfaces of selected hydrogeologic units within the Mississippi embayment aquifer system for use in additional ground-water investigations.
Map showing Mississippi Embayment.
The method used to create each digital hydrogeologic surface included interpretation of the altitude of the top of each hydrogeologic unit from over 2,750 geophysical logs. The geophysical logs were primarily from petroleum test wells and domestic and public supply water wells. Geophysical logs were chosen based on availability and spatial distribution. Resistivity and natural gamma logs were used to interpret the top of each unit of interest. Land-surface datums were determined and altitudes were calculated for nine hydrogeologic surfaces of the Mississippi embayment. Outcrop and subcrop extents were determined from published reports and/or from geophysical log interpretations. Thickness maps were constructed for each unit using the GIS to calculate the difference between the altitude of the interpreted top of the unit and the altitude of the interpreted top of the underlying unit.
For more information on the Mississippi Embayment Regional Aquifer Study (MERAS) project please visit the project's web page at the following URL: http://ar.water.usgs.gov/meras/index2.php
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