As part of the U.S. Geological Survey (USGS) Water Availability and Use Science Program study of the Mississippi Alluvial Plain (MAP), a shapefile representing seven generalized regions of the MAP extent as defined by Painter and Westerman (2018) was compiled. The generalized regions provide a framework for analysis, visualization, and regional comparisons of local data within the MAP. Regions north of the Red River were based on those described by Ackerman (1996). The Grand Prairie region includes the area north and east of the Arkansas River and south and west of the White River within the MAP. The Cache region includes the area north and east of the White River and the area generally west of Crowley’s Ridge, which lies outside of the MAP extent (Painter and Westerman, 2018), bisects the northern part of the MAP, and has elevations 100 to 250 feet (ft) higher than the MAP (Ackerman, 1996). The Delta region, which is roughly equivalent to the Yazoo River drainage, lies predominately in Mississippi and covers much of the area east of the Mississippi River within the MAP. The Boeuf region covers the area north of the Red River and the Little Old River - Mississippi River confluence, the area south of the Arkansas River, and the area west of the Delta region within the MAP. The St. Francis region lies generally east of Crowley’s Ridge and north of the Delta region in parts of Tennessee, Kentucky, Illinois, Missouri, and Arkansas. The regions south of the Red River and the Little Old River – Mississippi River confluence were based primarily on depositional environment (Saucier, 1994). The Atchafalaya region contains the Atchafalaya River. The Deltaic and Chenier Plains region lies south of the Atchafalaya region and covers the southernmost part of the MAP. In order to keep the regions contiguous, some relatively small parts of the Deltaic and Chenier Plains as defined by Saucier (1994) were included within the boundary of the Atchafalaya region defined for this study, and vice-versa. References Ackerman, D.J., 1996, Hydrology of the Mississippi River Valley alluvial aquifer, South-Central United States: U.S. Geological Survey Professional Paper 1416-D, 56 p., 8 pls. in pocket. Painter, J.A., and Westerman, D.A., 2018, Mississippi Alluvial Plain extent, November 2017: U.S. Geological Survey data release, https://doi.org/10.5066/F70R9NMJ. Saucier, R.T., 1994, Geomorphology and Quaternary geologic history of the Lower Mississippi Valley: U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Vols. I and II, 398 p., 28 pls.

The Mississippi Alluvial Plain (MAP) has become one of the most important agricultural regions in the US, and it relies heavily on a groundwater system that is poorly understood and shows signs of substantial change. The heavy use of the available groundwater resources has resulted in significant groundwater-level declines and reductions in base flow in streams within the MAP. These impacts are limiting well production and threatening future water-availability for the region. This product will help not only scientists in our center, but also at a national level. This product will also be part of a larger study encompassing the Mississippi Alluvial Plain region. The Mississippi Alluvial Plain extent was delineated using GIS tools to represent the geographic extent of the Mississippi Alluvial Aquifer through incorporation of elevation information, geomorphology knowledge, ecological region extent, and previously published extents for part of the MAP region. The current MAP extent represents version 1.0. Future changes to the MAP extent will be tracked through increasing version numbers.

The Mississippi Alluvial Plain (MAP) has become one of the most important agricultural regions in the US, and it relies heavily on a groundwater system that is poorly understood and shows signs of substantial change. The heavy use of the available groundwater resources has resulted in significant groundwater-level declines and reductions in base flow in streams within the MAP. These impacts are limiting well production and threatening future water-availability for the region. This product will help not only scientists in our center, but also at a national level. This product will also be part of a larger study encompassing the Mississippi Alluvial Plain region. The Mississippi Alluvial Plain extent was delineated using GIS tools to represent the geographic extent of the Mississippi Alluvial Aquifer through incorporation of elevation information, geomorphology knowledge, ecological region extent, and previously published extents for part of the MAP region. The current MAP extent represents version 1.0. Future changes to the MAP extent will be tracked through increasing version numbers.

A digital dataset of the geomorphology of the Lower Mississippi River Valley in Missouri, Kentucky, Arkansas, Tennessee, Louisiana, and Mississippi was developed from Roger T. Saucier’s “Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley, Volumes I and II” (1994) as part of the Mississippi Alluvial Plain (MAP) Regional Water Availability Study. The maps included in the 1994 reports provide a comprehensive overview of the previously misunderstood alluvial valley geology and characterize twenty-nine Pleistocene and Holocene alluvial deposits, such as point bars, abandoned channels, backswamps, and natural levees. Each map was georeferenced to North American Datum 1983 and projected to USA Contiguous Albers Equal Conic (U.S. Geological Survey version) projection (standard parallels 29.5 and 45.5 degrees, central meridian -96 degrees, and latitude of origin 23 degrees). Once georeferenced (using ArcMap v 10.4.1), individual geomorphological features were digitized manually. Each polygon was validated using a geodatabase topology and the Topology Editor tools in ArcMap; this step was completed to create individual polygons without gaps or overlap. Efforts were made to match colors in the original map legend to the digital product, with the exception of a few features listed in the original key (for example, feature “Pve” does not match the exact color in the plates). Updated colors were selected to ease the distinction between similarly colored features. Saucier envisioned his work to be utilized by engineering geologists conducting studies that were focused at both the local and regional scale in the Lower Mississippi River Valley (Saucier, 1994). Creating a digital dataset of Saucier’s seminal geomorphological work increases the usability of the map layers for current and future scientific investigations focused on regional groundwater availability in the Mississippi Alluvial Plain. References Saucier, R.T., 1994, Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley: U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Vols. I and II, 398 p. and 28 plates

A digital dataset of the geomorphology of the Lower Mississippi River Valley in Missouri, Kentucky, Arkansas, Tennessee, Louisiana, and Mississippi was developed from Roger T. Saucier’s “Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley, Volumes I and II” (1994) as part of the Mississippi Alluvial Plain (MAP) Regional Water Availability Study. The maps included in the 1994 reports provide a comprehensive overview of the previously misunderstood alluvial valley geology and characterize twenty-nine Pleistocene and Holocene alluvial deposits, such as point bars, abandoned channels, backswamps, and natural levees. Each map was georeferenced to North American Datum 1983 and projected to USA Contiguous Albers Equal Conic (U.S. Geological Survey version) projection (standard parallels 29.5 and 45.5 degrees, central meridian -96 degrees, and latitude of origin 23 degrees). Once georeferenced (using ArcMap v 10.4.1), individual geomorphological features were digitized manually. Each polygon was validated using a geodatabase topology and the Topology Editor tools in ArcMap; this step was completed to create individual polygons without gaps or overlap. Efforts were made to match colors in the original map legend to the digital product, with the exception of a few features listed in the original key (for example, feature “Pve” does not match the exact color in the plates). Updated colors were selected to ease the distinction between similarly colored features. Saucier envisioned his work to be utilized by engineering geologists conducting studies that were focused at both the local and regional scale in the Lower Mississippi River Valley (Saucier, 1994). Creating a digital dataset of Saucier’s seminal geomorphological work increases the usability of the map layers for current and future scientific investigations focused on regional groundwater availability in the Mississippi Alluvial Plain. References Saucier, R.T., 1994, Geomorphology and Quaternary Geologic History of the Lower Mississippi Valley: U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, Vols. I and II, 398 p. and 28 plates

Outcrop and subcrop extent of the Mississippi River Valley Alluvial Aquifer in Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, and Tennessee.

A potentiometric surface map for spring 2016 was created for the Mississippi River Valley alluvial (MRVA) aquifer, which was referenced to the North American Vertical Datum of 1988 (NAVD 88), using most of the available groundwater-altitude data from wells and surface-water-altitude data from streamgages. Most of the wells were measured annually or one time, after installation, but some wells were measured more than one time in a year and a small number of wells were measured continually. Streamgages were typically operated continuously. The potentiometric surface map for 2016 was created as part of the U.S. Geological Survey (USGS) Water Availability and Use Science Program to support investigations that characterize the MRVA aquifer. The potentiometric contours ranged from 10 feet to 340 feet above NAVD 88. The regional direction of groundwater flow was generally towards the south-southwest, except in areas of groundwater-altitude depressions, where groundwater flows into the depressions, and near rivers, where groundwater flow generally parallels the flow in the rivers. There are large depressions in the potentiometric surface in the lower half of the Cache region and in most of the Grand Prairie and Delta regions.

A potentiometric surface map for spring 2016 was created for the Mississippi River Valley alluvial (MRVA) aquifer, which was referenced to the North American Vertical Datum of 1988 (NAVD 88), using most of the available groundwater-altitude data from wells and surface-water-altitude data from streamgages. Most of the wells were measured annually or one time, after installation, but some wells were measured more than one time in a year and a small number of wells were measured continually. Streamgages were typically operated continuously. The potentiometric surface map for 2016 was created as part of the U.S. Geological Survey (USGS) Water Availability and Use Science Program to support investigations that characterize the MRVA aquifer. The potentiometric contours ranged from 10 feet to 340 feet above NAVD 88. The regional direction of groundwater flow was generally towards the south-southwest, except in areas of groundwater-altitude depressions, where groundwater flows into the depressions, and near rivers, where groundwater flow generally parallels the flow in the rivers. There are large depressions in the potentiometric surface in the lower half of the Cache region and in most of the Grand Prairie and Delta regions.

This data set represents the extent of the Mississippi River Valley alluvial aquifer in the states of Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.

This data set represents the extent of the Mississippi River Valley alluvial aquifer in the states of Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.