Monthly rollup of the discrete and daily-aligned groundwater levels were created from Robinson, Asquith, and Seanor (2020) data products with removal of the paired groundwater and surface-water sites listed by Robinson, Killian, and Asquith (2020). The monthly rollup is composed of (1) computed monthly "mean" values regardless of whether a well had one measurement in the month or up to about 30 days of daily-mean values, (2) standard deviation of the water levels within the month (sample size is generally just one day but for recorder sites could be up to about 30 days), (3) the last water level in the month, and (4) monthly counts of water levels. The algorithm is available within the sources of visGWDBmrva (Asquith and others, 2019). A comment is made that the string 1980-01-01_2019-12-31 is retained in the file naming to parallel that for Robinson, Asquith, and Seanor (2020) files although the day of the month has no meaning for a monthly rollup. There are 18,736 unique wells of statistics; 18,736 wells in the metadata; and 107,568 year-month entries in the monthly rollup product. References: Asquith, W.H., Seanor, R.C., McGuire, V.L. (contributor), and Kress, W.H. (contributor), 2019, Source code in R to quality assure, plot, summarize, interpolate, and extend groundwater-level information, visGWDB—Groundwater-level informatics with demonstration for the Mississippi River Valley alluvial aquifer: U.S. Geological Survey software release, Reston, Va., https://doi.org/10.5066/P9W004O6.

A combination of discrete and daily-aligned groundwater levels for the Mississippi River Valley alluvial aquifer clipped to the Mississippi Alluvial Plain, as defined by Painter and Westerman (2018), with corresponding metadata are based on processing of U.S. Geological Survey National Water Information System (NWIS) (U.S. Geological Survey, 2020) data. The processing was made after retrieval using aggregation and filtering through the infoGW2visGWDB software (Asquith and Seanor, 2019). The nomenclature GWmaster mimics that of the output from infoGW2visGWDB. Two separate data retrievals for NWIS were made. First, the discrete data were retrieved, and second, continuous records from recorder sites with daily-mean or other daily statistics codes were retrieved. Each dataset was separately passed through the infoGW2visGWDB software to create a "GWmaster discrete" and "GWmaster continuous" and these tables were combined and then sorted on the site identifier and date to form the data products described herein. A sweep through the combined dataset (the "database") was made to isolate duplicate observations, or observations for the same well and on the same day. If a discrete value was present, it was retained as authoritative for the day and in descending order of priority daily-mean, daily-maximum, and daily minimum. Therefore, only a single record for a well and day are present in the dataset. The duplicate search removed 876 records and 31 wells were involved; in total, this is about 0.3 percent of the database. References: Asquith, W.H., Seanor, R.C., 2019, infoGW2visGWDB—An R groundwater data-processing utility for manipulating, checking the veracity, and converting an "infoGW" object to the "GWmaster" object for the visGWDB software with demonstration for the Mississippi River Valley alluvial aquifer: U.S. Geological Survey software release, Reston, Va., https://doi.org/10.5066/P9MK0B6L. 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. U.S. Geological Survey, 2020, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed April 2, 2020, at https://doi.org/10.5066/F7P55KJN.

This dataset contains the contours, in feet, of the potentiometric-surface, spring 2020, Mississippi River Valley alluvial aquifer (MRVA). The contours are referenced to the North American Vertical Datum of 1988 (NAVD 88). The contours were derived from most of the available groundwater-altitude (GWA) data from wells and surface-water-altitude (SWA) data from streamgages, measured in for spring 2020. The potentiometric contours ranged from 10 to 340 feet (3 to 104 meters) 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.

This dataset contains the contours, in feet, of the potentiometric-surface, spring 2018, Mississippi River Valley alluvial (MRVA) aquifer. The contours are referenced to the North American Vertical Datum of 1988 (NAVD 88). The contours were derived from most of the available groundwater-altitude data from wells and surface-water-altitude data from streamgages, measured in for spring 2018. The potentiometric contours ranged from 10 to 340 feet (3 to 104 meters) 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.

This dataset contains the contours, in feet, of the potentiometric-surface, spring 2020, Mississippi River Valley alluvial aquifer (MRVA). The contours are referenced to the North American Vertical Datum of 1988 (NAVD 88). The contours were derived from most of the available groundwater-altitude (GWA) data from wells and surface-water-altitude (SWA) data from streamgages, measured in for spring 2020. The potentiometric contours ranged from 10 to 340 feet (3 to 104 meters) 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.

This dataset contains groundwater (GW)-altitude (ALT) data from wells that was used or considered to create a potentiometric-surface map for the Mississippi River Valley alluvial (MRVA) aquifer for spring 2018. The groundwater-altitude data was referenced to the North American Vertical Datum of 1988 (NAVD 88). Most of the wells were measured annually, but some wells were measured more than one time in a year and a small number of wells were measured continuously. Groundwater-altitude data were from wells measured in spring 2018. Spring-time measurements were preferred because water levels had generally recovered from pumping during the previous irrigation season and it was before pumping began for the current irrigation season. To best reflect hydrologic conditions in the MRVA aquifer, the groundwater altitudes used to create the 2018 potentiometric surface would be measured in a short-time frame of days or a week and there would be available data (for example from sets of wells with short-screen (about 5 to 10 feet or 1.5 to 3 meters) installed near the top, in the middle, and near the bottom of the aquifer) to indicate vertical flow components. However, most wells screened in the MRVA aquifer were measured before the potentiometric-surface map of the MRVA aquifer was planned and therefore the timing of each well’s measurement(s) was determined by the needs and schedules of the entities doing the measurements. Also, many of the measured wells had longer screens (from greater than 10 feet or 3 meters and covering a substantial part of the aquifer thickness), therefore their water-level measurements represent an average head in the aquifer for that location. The resultant potentiometric-surface contours and raster represents the generalized central tendency for spring 2018, but it would not be useful for some purposes, such as for calibration of a groundwater-flow model for early April 2018 or for some local scale assessments.

This dataset contains groundwater (GW)-altitude (ALT) data from wells that was used or considered to create a potentiometric-surface map for the Mississippi River Valley alluvial (MRVA) aquifer for spring 2018. The groundwater-altitude data was referenced to the North American Vertical Datum of 1988 (NAVD 88). Most of the wells were measured annually, but some wells were measured more than one time in a year and a small number of wells were measured continuously. Groundwater-altitude data were from wells measured in spring 2018. Spring-time measurements were preferred because water levels had generally recovered from pumping during the previous irrigation season and it was before pumping began for the current irrigation season. To best reflect hydrologic conditions in the MRVA aquifer, the groundwater altitudes used to create the 2018 potentiometric surface would be measured in a short-time frame of days or a week and there would be available data (for example from sets of wells with short-screen (about 5 to 10 feet or 1.5 to 3 meters) installed near the top, in the middle, and near the bottom of the aquifer) to indicate vertical flow components. However, most wells screened in the MRVA aquifer were measured before the potentiometric-surface map of the MRVA aquifer was planned and therefore the timing of each well’s measurement(s) was determined by the needs and schedules of the entities doing the measurements. Also, many of the measured wells had longer screens (from greater than 10 feet or 3 meters and covering a substantial part of the aquifer thickness), therefore their water-level measurements represent an average head in the aquifer for that location. The resultant potentiometric-surface contours and raster represents the generalized central tendency for spring 2018, but it would not be useful for some purposes, such as for calibration of a groundwater-flow model for early April 2018 or for some local scale assessments.

This dataset contains groundwater-altitude (GWA) data from wells that were used or considered (indicated by the field USE_2020) to create a potentiometric-surface map for the Mississippi River Valley alluvial aquifer (MRVA) for spring 2020. The GWA data was referenced to the North American Vertical Datum of 1988 (NAVD 88). Most of the wells were measured annually, but some wells were measured more than one time in a year and a small number of wells were measured continuously. GWA data were from wells measured in spring 2020. To best reflect hydrologic conditions in the MRVA, the GWA data used to create the 2020 potentiometric surface would be measured in a short-time frame of days or a week and there would be available data (for example from sets of wells with short-screen (about 5 to 10 feet or 1.5 to 3 meters) installed near the top, in the middle, and near the bottom of the aquifer) to indicate vertical flow components. However, most wells screened in the MRVA were measured before the potentiometric-surface map of the MRVA was planned and therefore the timing of each well's measurement(s) was determined by the needs and schedules of the entities doing the measurements. Also, many of the measured wells had longer screens (from greater than 10 feet or 3 meters and covering a substantial part of the aquifer thickness), therefore their water-level measurements represent an average head in the aquifer for that location. The resultant potentiometric-surface contours and raster represents the generalized central tendency for spring 2020, but it would not be useful for some purposes, such as for calibration of a groundwater-flow model for early April 2020 or for some local scale assessments.

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 dataset contains groundwater-altitude (GWA) data from wells that were used or considered (indicated by the field USE_2020) to create a potentiometric-surface map for the Mississippi River Valley alluvial aquifer (MRVA) for spring 2020. The GWA data was referenced to the North American Vertical Datum of 1988 (NAVD 88). Most of the wells were measured annually, but some wells were measured more than one time in a year and a small number of wells were measured continuously. GWA data were from wells measured in spring 2020. To best reflect hydrologic conditions in the MRVA, the GWA data used to create the 2020 potentiometric surface would be measured in a short-time frame of days or a week and there would be available data (for example from sets of wells with short-screen (about 5 to 10 feet or 1.5 to 3 meters) installed near the top, in the middle, and near the bottom of the aquifer) to indicate vertical flow components. However, most wells screened in the MRVA were measured before the potentiometric-surface map of the MRVA was planned and therefore the timing of each well's measurement(s) was determined by the needs and schedules of the entities doing the measurements. Also, many of the measured wells had longer screens (from greater than 10 feet or 3 meters and covering a substantial part of the aquifer thickness), therefore their water-level measurements represent an average head in the aquifer for that location. The resultant potentiometric-surface contours and raster represents the generalized central tendency for spring 2020, but it would not be useful for some purposes, such as for calibration of a groundwater-flow model for early April 2020 or for some local scale assessments.