A three-dimensional groundwater flow model (MODFLOW-2005) of the Mississippi embayment, South-Central United States, was developed as part of a national project initiated by the U.S. Geological Survey Groundwater Resources Program to provide updated assessments of groundwater availability in important principal aquifers across the United States. The goals of the national assessment are to document effects of human activities on water levels and groundwater storage, explore climate variability effects on the regional water budget, and evaluate the adequacy of data networks at a regional scale. The Mississippi embayment was chosen because of the substantial dependency on groundwater for agriculture and municipal needs. Since the development of the original Mississippi Embayment Regional Aquifer system (MERAS) model in 2009, the model has been updated and enhanced and is proving an invaluable tool to evaluate and develop water management pumping strategies. The construction and calibration of the original model (MERAS 1.0) is documented in the U.S. Geological Survey (USGS) Scientific Investigations Report 2009-5172 (https://doi.org/10.3133/sir20095172). MERAS 1.0 contains one transient simulation that quantifies the groundwater availability in the aquifer system from January 1870 to April 2007. The USGS Professional Paper 1785 (https://doi.org/10.3133/pp1785) describes the historical background of the hydrologic system, analyses of the transient water budget, effects of climate change on the groundwater system, and evaluation of the groundwater monitoring network. Minor modifications were done to the model to improve the simulation of groundwater flow (MERAS 1.1) and two climate scenarios were completed using this model. USGS Scientific Investigations Report 2013-5161 (https://doi.org/10.3133/sir20135161) investigated ways to improve the match of observed to simulated groundwater levels within the Mississippi River Valley alluvial and middle Claiborne (Sparta) aquifers. The model was updated with improved water-use estimates and refined parameter estimation by using pilot points (MERAS 2.0). Three water-supply scenarios considered by the State of Arkansas were completed with the MERAS 2.0 model. To assess proposed alternative water-supply scenarios and their impact on future water-supply in the Mississippi Delta, the USGS and the Mississippi Department of Environmental Quality collaborated to update and enhance the MERAS 2.0 model. The MERAS 2.0 model has been updated to April 2014 with the most recent water-use data, precipitation and recharge data, and streamflow and water-level observation data to make MERAS version 2.1 (https://doi.org/10.3133/sir20195116). Five different water-supply options (with a total of 22 sub-scenarios) are run using the MERAS 2.1 model and include: irrigation efficiency, on-farm storage and tailwater recovery, weirs for surface-water augmentation, surface-water transfer, and groundwater transfer and injection. All scenarios are compared with a base scenario which provides a standard for the alternate water-management scenarios. This USGS data release contains all of the input and output files for the simulation of these water-supply option using the new MERAS 2.1 model described in the associated model documentation report (https://doi.org/10.3133/sir20195116).

In 2018 The U.S. Geological Survey, in cooperation with the U.S. Bureau of Reclamation and the Oklahoma Water Resources Board, published a calibrated numerical groundwater- flow model and associated model documentation report that evaluated the effects of potential groundwater withdrawals on groundwater flow and availability in the Rush Springs aquifer in western Oklahoma. The results of groundwater-availability scenarios run on the calibrated numerical groundwater-flow model could be used by the Oklahoma Water Resources Board to evaluate the maximum annual yield of groundwater from the Rush Springs aquifer in Oklahoma. A conceptual groundwater-flow model is a simplified description of the major inflow and outflow sources (hydrologic boundaries) of a groundwater-flow system as well as an accounting of the estimated mean flows from those sources (water budget) for a specified period of time. The conceptual model was necessary to provide constraints used in the construction and calibration of a scientifically defensible numerical groundwater-flow model that reasonably represents the groundwater-flow system. A finite-difference numerical groundwater-flow model of the Rush Springs aquifer was constructed by using MODFLOW-2005 with the Newton formulation solver (MODFLOW-NWT). Data inputs for each package were specified in machine-readable text files. The numerical model of the Rush Springs aquifer had 1,362 rows, 1,083 columns, about 554,000 active cells of 500 by 500 ft, and 3 convertible layers. The top layer (layer 1) represented the Permian-age Cloud Chief Formation. The Rush Springs aquifer is composed of Permian-age Whitehorse Group. The second layer (layer 2) represented the undifferentiated Quaternary-age alluvium and terrace deposits, as well as the upper 30 ft of the Whitehorse Group. The bottom layer (layer 3) represented the remainder of the Rush Springs Formation. The model active area was modified from Neel and others (2018). The numerical model was temporally discretized into 444 monthly transient stress periods representing the period 1979-2015. An initial steady-state stress period, in which the groundwater-flow equation had no storage component, represented mean annual inflows to and outflows from the aquifer and produced a solution that was used as the initial condition for subsequent transient stress periods. The numerical model was constructed in units of meters and days. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20185136)

In 2018 The U.S. Geological Survey, in cooperation with the U.S. Bureau of Reclamation and the Oklahoma Water Resources Board, published a calibrated numerical groundwater- flow model and associated model documentation report that evaluated the effects of potential groundwater withdrawals on groundwater flow and availability in the Rush Springs aquifer in western Oklahoma. The results of groundwater-availability scenarios run on the calibrated numerical groundwater-flow model could be used by the Oklahoma Water Resources Board to evaluate the maximum annual yield of groundwater from the Rush Springs aquifer in Oklahoma. A conceptual groundwater-flow model is a simplified description of the major inflow and outflow sources (hydrologic boundaries) of a groundwater-flow system as well as an accounting of the estimated mean flows from those sources (water budget) for a specified period of time. The conceptual model was necessary to provide constraints used in the construction and calibration of a scientifically defensible numerical groundwater-flow model that reasonably represents the groundwater-flow system. A finite-difference numerical groundwater-flow model of the Rush Springs aquifer was constructed by using MODFLOW-2005 with the Newton formulation solver (MODFLOW-NWT). Data inputs for each package were specified in machine-readable text files. The numerical model of the Rush Springs aquifer had 1,362 rows, 1,083 columns, about 554,000 active cells of 500 by 500 ft, and 3 convertible layers. The top layer (layer 1) represented the Permian-age Cloud Chief Formation. The Rush Springs aquifer is composed of Permian-age Whitehorse Group. The second layer (layer 2) represented the undifferentiated Quaternary-age alluvium and terrace deposits, as well as the upper 30 ft of the Whitehorse Group. The bottom layer (layer 3) represented the remainder of the Rush Springs Formation. The model active area was modified from Neel and others (2018). The numerical model was temporally discretized into 444 monthly transient stress periods representing the period 1979-2015. An initial steady-state stress period, in which the groundwater-flow equation had no storage component, represented mean annual inflows to and outflows from the aquifer and produced a solution that was used as the initial condition for subsequent transient stress periods. The numerical model was constructed in units of meters and days. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20185136)

This model archive contains the model files for the MERAS 3 and Mississippi Delta groundwater flow models documented in the U.S. Geological Survey Scientific Investigations Report 2023-5100. The MERAS 3 model provides a simplified representation of groundwater flow in the Mississippi Embayment Regional Aquifer Study (MERAS) area for the period of 1900 through 2018, with the primary goal of providing boundary fluxes for inset models focused on local areas of interest. The Mississippi Delta model simulates groundwater flow in the Delta region of northwestern Mississippi from 1900 through 2018, using boundary fluxes from the MERAS 3 model. A scenario version of the Mississippi Delta model extends the simulation to 2056, using net infiltration, surface water runoff, and irrigation pumping derived from downscaled general circulation model output, via a soil water balance simulation. Workflows for initial model construction, parameter estimation, and the setup of future climate scenarios are included in separate ZIP archives, along with portable python distributions for running the workflow scripts on OSX or Windows platforms. See the Readme.md file(s) for instructions.

An existing three-dimensional model (MODFLOW-2000) by Fine, Petkewich, and Campbell (2017) (https://doi.org/10.3133/sir20175128) was used to evaluate 7 water-management scenarios and predict the effects on the groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. This model was originally developed in 2007, by Petkewich and Campbell (https://pubs.er.usgs.gov/publication/sir20075126), then updated and recalibrated to conditions from 1900 to 2015. Results of six previous scenario simulations (scenarios 1-6) for the Mount Pleasant Water Works are published in a U.S. Geological Survey (USGS) Scientific Investigations Report (https://doi.org/10.3133/sir20175128). The archived model input and output files are available in a USGS data release (https://doi.org/10.5066/F7S181FC). Seven additional MODFLOW-2000 scenarios (numbered 7-13), using this updated and recalibrated model, were developed to evaluate different withdrawal strategies which are included in this data release: (7) Mount Pleasant Waterworks bringing online a new well (located at the old well 5 location) at 3.51 million gallons per day (Mgal/d) in 2025; (8) Maximizing withdrawals from Mount Pleasant Waterworks wells 2 and 5 (3.51 Mgal/d each) in 2020 and 2025, respectively; (9) Same as Scenario 7, but removing well 3 from production in 2025; (10) Same as Scenario 9, but removing well 4 from production in 2025 (11) Same as Scenario 7, but converting well 3 to an injection well in 2025 (12) Same as Scenario 11, but converting well 4 to an injection well in 2030; and (13) Same as scenario 8, but with two injection wells added (one in 2025 and one in 2035) to Mount Pleasant Waterworks well field. Nine alternate simulations for scenarios 11-13 (three MODFLOW and six MODPATH) were done to evaluate the effects of different porosity on the groundwater flow system, water levels, and the time-of-travel of particles from injection wells to the main water source. This USGS data release contains all the input and output files for the simulations described above and in the readme.txt file of this data release (https://doi.org/10.5066/P9GZEE4E).

An existing three-dimensional model (MODFLOW-2000) by Fine, Petkewich, and Campbell (2017) (https://doi.org/10.3133/sir20175128) was used to evaluate 7 water-management scenarios and predict the effects on the groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. This model was originally developed in 2007, by Petkewich and Campbell (https://pubs.er.usgs.gov/publication/sir20075126), then updated and recalibrated to conditions from 1900 to 2015. Results of six previous scenario simulations (scenarios 1-6) for the Mount Pleasant Water Works are published in a U.S. Geological Survey (USGS) Scientific Investigations Report (https://doi.org/10.3133/sir20175128). The archived model input and output files are available in a USGS data release (https://doi.org/10.5066/F7S181FC). Seven additional MODFLOW-2000 scenarios (numbered 7-13), using this updated and recalibrated model, were developed to evaluate different withdrawal strategies which are included in this data release: (7) Mount Pleasant Waterworks bringing online a new well (located at the old well 5 location) at 3.51 million gallons per day (Mgal/d) in 2025; (8) Maximizing withdrawals from Mount Pleasant Waterworks wells 2 and 5 (3.51 Mgal/d each) in 2020 and 2025, respectively; (9) Same as Scenario 7, but removing well 3 from production in 2025; (10) Same as Scenario 9, but removing well 4 from production in 2025 (11) Same as Scenario 7, but converting well 3 to an injection well in 2025 (12) Same as Scenario 11, but converting well 4 to an injection well in 2030; and (13) Same as scenario 8, but with two injection wells added (one in 2025 and one in 2035) to Mount Pleasant Waterworks well field. Nine alternate simulations for scenarios 11-13 (three MODFLOW and six MODPATH) were done to evaluate the effects of different porosity on the groundwater flow system, water levels, and the time-of-travel of particles from injection wells to the main water source. This USGS data release contains all the input and output files for the simulations described above and in the readme.txt file of this data release (https://doi.org/10.5066/P9GZEE4E).

A previously published groundwater flow model (https://pubs.usgs.gov/sir/2005/5089/) was revised with refined grid spacing and updated hydrogeolgic framework and hydrologic properties (http://doi.org/10.3133/sir20155061) and used in this study to predict the effects of Upper Floridan aquifer (UFA) groundwater pumpage on horizontal hydraulic-head gradients in the upper-water-bearing zone of the UFA in the downtown Brunswick area, Glynn County, Georgia. The model used MOFLOW-2000 and was calibrated using groundwater-use information for October 2015, which was the basis for the 2015 Base Case simulation. A comparison of the 2015 Base Case simulation with seven groundwater-management scenarios evaluated potential changes to the upper-water-bearing zone of the UFA near downtown Brunswick. Particle-tracking analysis, using MODPATH, provided pathlines and time-of-travel for the 2015 Base Case simulation and scenario C. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20195035).

A previously published groundwater flow model (https://pubs.usgs.gov/sir/2005/5089/) was revised with refined grid spacing and updated hydrogeolgic framework and hydrologic properties (http://doi.org/10.3133/sir20155061) and used in this study to predict the effects of Upper Floridan aquifer (UFA) groundwater pumpage on horizontal hydraulic-head gradients in the upper-water-bearing zone of the UFA in the downtown Brunswick area, Glynn County, Georgia. The model used MOFLOW-2000 and was calibrated using groundwater-use information for October 2015, which was the basis for the 2015 Base Case simulation. A comparison of the 2015 Base Case simulation with seven groundwater-management scenarios evaluated potential changes to the upper-water-bearing zone of the UFA near downtown Brunswick. Particle-tracking analysis, using MODPATH, provided pathlines and time-of-travel for the 2015 Base Case simulation and scenario C. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20195035).

An existing three-dimensional model (MODFLOW-2000) by Petkewich and Campbell (2007) (https://pubs.usgs.gov/sir/2007/5126/) was updated to simulate six predictive water-management scenarios that were created to simulate potential changes in groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. The model was recalibrated to conditions from 1900 to 2015. Simulations included six scenarios: (1) maximize Mount Pleasant Waterworks reverse-osmosis plant capacity by increasing groundwater withdrawals from 3.9 million gallons per day (Mgal/d) in 2015 to 8.6 Mgal/d from the Middendorf aquifer; (2) same as Scenario 1, but with the addition of a 0.5 Mgal/d supply well in the Middendorf aquifer near Moncks Corner, SC; (3) same as Scenario 1, but with the addition of a 1.5 Mgal/d supply well in the Middendorf aquifer near Moncks Corner, SC; (4) maximize Mount Pleasant Waterworks well capacity by increasing withdrawals from the Middendorf aquifer from 3.9 Mgal/d in 2015 to 10.2 Mgal/d (5) minimizing Mount Pleasant Waterworks surface-water purchase from the Charleston Water System by adding supply wells and increasing withdrawals from the Middendorf aquifer from 3.9 Mgal/d in 2015 to 12.2 Mgal/d; and (6) same as Scenario 1, but with the addition of quarterly model stress periods to simulate seasonal variations in the groundwater withdrawals. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20175128).

An existing three-dimensional model (MODFLOW-2000) by Petkewich and Campbell (2007) (https://pubs.usgs.gov/sir/2007/5126/) was updated to simulate six predictive water-management scenarios that were created to simulate potential changes in groundwater flow and groundwater-level conditions in the Mount Pleasant, South Carolina area. The model was recalibrated to conditions from 1900 to 2015. Simulations included six scenarios: (1) maximize Mount Pleasant Waterworks reverse-osmosis plant capacity by increasing groundwater withdrawals from 3.9 million gallons per day (Mgal/d) in 2015 to 8.6 Mgal/d from the Middendorf aquifer; (2) same as Scenario 1, but with the addition of a 0.5 Mgal/d supply well in the Middendorf aquifer near Moncks Corner, SC; (3) same as Scenario 1, but with the addition of a 1.5 Mgal/d supply well in the Middendorf aquifer near Moncks Corner, SC; (4) maximize Mount Pleasant Waterworks well capacity by increasing withdrawals from the Middendorf aquifer from 3.9 Mgal/d in 2015 to 10.2 Mgal/d (5) minimizing Mount Pleasant Waterworks surface-water purchase from the Charleston Water System by adding supply wells and increasing withdrawals from the Middendorf aquifer from 3.9 Mgal/d in 2015 to 12.2 Mgal/d; and (6) same as Scenario 1, but with the addition of quarterly model stress periods to simulate seasonal variations in the groundwater withdrawals. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20175128).