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.

Seventy-five steady-state two-dimensional groundwater flow (MODFLOW-6) models of the shallow groundwater system were developed to map depth to water and estimate effective surficial transmissivity for the contiguous United States (CONUS). The models were driven by spatially-distributed recharge estimated by Reitz et al. (https://doi.org/10.5066/F7PN93P0) using average water-budget information for 1985-2015 and calibrated against long-term average water levels in observation wells, as well as, water-level estimates derived from perennial first-order streams and wetlands. The development of the model input and output files included in this data release, as well as post-processing used to derive additional water-budget components also included in this data release, are documented in the Water Resources Research article (https://doi.org/10.1029/2019WR026724).

Seventy-five steady-state two-dimensional groundwater flow (MODFLOW-6) models of the shallow groundwater system were developed to map depth to water and estimate effective surficial transmissivity for the contiguous United States (CONUS). The models were driven by spatially-distributed recharge estimated by Reitz et al. (https://doi.org/10.5066/F7PN93P0) using average water-budget information for 1985-2015 and calibrated against long-term average water levels in observation wells, as well as, water-level estimates derived from perennial first-order streams and wetlands. The development of the model input and output files included in this data release, as well as post-processing used to derive additional water-budget components also included in this data release, are documented in the Water Resources Research article (https://doi.org/10.1029/2019WR026724).

This model archive provides the necessary documentation of the numerical models developed for the Central Sands Lake study in central Wisconsin and will be included as a technical appendix (Appendix C) in the report to the Wisconsin State Legislature by the Wisconsin Department of Natural Resources (WDNR) in response to 2017 Wisconsin Act 10. This legislation directed DNR to determine whether existing and potential groundwater withdrawals are causing or are likely to cause significant reduction of mean seasonal water levels at Pleasant Lake, Long Lake, and Plainfield Lake (s. 281.34(7m)(2)(b), Wis. Stats.) in Waushara County, Wisconsin. To evaluate the potential hydrologic connection between groundwater withdrawals and the nearby study lakes, hydrologic models were created that focused on the lakes of interest and yet were large enough to cover a broad enough region to extend to the major hydrologic boundaries of the natural flow system. The areas near the lakes require finer-scale grid discretization (or spacing) to better represent the lakes and streams in the model, but also need to cover a large enough area to include the groundwater withdrawal locations that have the potential to cause reduction in water levels in the lakes. To accomplish these goals, three groundwater models were created: a regional model extending to major hydrologic boundaries; and two inset models, inheriting boundaries from the regional model but focused near the lakes. Each of the inset models, in turn, included a detailed area close to the lakes surrounded by an area at the same spatial scale as the regional model. To support WDNR in evaluating the connection between groundwater withdrawals and lake levels, a representative time period was required over which to compare land use with and without irrigated agriculture and for WDNR to evaluate potential lake stage and flux changes related to irrigated agriculture. WDNR chose the climate period of 1981-2018 to be representative of a typical period and provided two land use scenarios—one with no irrigated agriculture and one with assumed crop rotations similar to current conditions—to simulate with groundwater models to, then, compare lake responses with. As a result, simulations over this climate record are not intended to recreate the history of 1981-2018 because land use changed over that time. These runs are, instead, intended to provide a basis on which to compare land use with and without irrigation-related groundwater withdrawals based on the current arrangement of land use and a varied climatic record. Groundwater withdrawals focused on irrigated-agriculture-related water use because greater than 95% of groundwater withdrawal in the two inset models around the study lakes is for irrigated agriculture water use. The period of 2012-2018 was used for parameter estimation (synonymously referred to as “history matching”) for the groundwater models. This time period was chosen because it includes the most complete water use records to simulate groundwater withdrawals. History matching was performed using groundwater elevations, lake stages, and streamflow observations over the 2012-2018 time period and processed observations derived from those raw data. Climatic data were incorporated into the model using a soil-water balance approach. A soil water balance model (Westenbroek and others, 2021) was constructed at the scale of the regional groundwater model to both calculate recharge based on land use and climate, and in the long-term climate-period runs, to estimate water use required by irrigated agriculture to apply as well boundary conditions in the groundwater model in the absence of reported water use values over that period. The model archive presents all the inputs needed to run the models, the model software, information on history matching to estimate parameters of the model, model scenario files, and model outputs that the user should be able to recreate using the model files in this archive.

This model archive provides the necessary documentation of the numerical models developed for the Central Sands Lake study in central Wisconsin and will be included as a technical appendix (Appendix C) in the report to the Wisconsin State Legislature by the Wisconsin Department of Natural Resources (WDNR) in response to 2017 Wisconsin Act 10. This legislation directed DNR to determine whether existing and potential groundwater withdrawals are causing or are likely to cause significant reduction of mean seasonal water levels at Pleasant Lake, Long Lake, and Plainfield Lake (s. 281.34(7m)(2)(b), Wis. Stats.) in Waushara County, Wisconsin. To evaluate the potential hydrologic connection between groundwater withdrawals and the nearby study lakes, hydrologic models were created that focused on the lakes of interest and yet were large enough to cover a broad enough region to extend to the major hydrologic boundaries of the natural flow system. The areas near the lakes require finer-scale grid discretization (or spacing) to better represent the lakes and streams in the model, but also need to cover a large enough area to include the groundwater withdrawal locations that have the potential to cause reduction in water levels in the lakes. To accomplish these goals, three groundwater models were created: a regional model extending to major hydrologic boundaries; and two inset models, inheriting boundaries from the regional model but focused near the lakes. Each of the inset models, in turn, included a detailed area close to the lakes surrounded by an area at the same spatial scale as the regional model. To support WDNR in evaluating the connection between groundwater withdrawals and lake levels, a representative time period was required over which to compare land use with and without irrigated agriculture and for WDNR to evaluate potential lake stage and flux changes related to irrigated agriculture. WDNR chose the climate period of 1981-2018 to be representative of a typical period and provided two land use scenarios—one with no irrigated agriculture and one with assumed crop rotations similar to current conditions—to simulate with groundwater models to, then, compare lake responses with. As a result, simulations over this climate record are not intended to recreate the history of 1981-2018 because land use changed over that time. These runs are, instead, intended to provide a basis on which to compare land use with and without irrigation-related groundwater withdrawals based on the current arrangement of land use and a varied climatic record. Groundwater withdrawals focused on irrigated-agriculture-related water use because greater than 95% of groundwater withdrawal in the two inset models around the study lakes is for irrigated agriculture water use. The period of 2012-2018 was used for parameter estimation (synonymously referred to as “history matching”) for the groundwater models. This time period was chosen because it includes the most complete water use records to simulate groundwater withdrawals. History matching was performed using groundwater elevations, lake stages, and streamflow observations over the 2012-2018 time period and processed observations derived from those raw data. Climatic data were incorporated into the model using a soil-water balance approach. A soil water balance model (Westenbroek and others, 2021) was constructed at the scale of the regional groundwater model to both calculate recharge based on land use and climate, and in the long-term climate-period runs, to estimate water use required by irrigated agriculture to apply as well boundary conditions in the groundwater model in the absence of reported water use values over that period. The model archive presents all the inputs needed to run the models, the model software, information on history matching to estimate parameters of the model, model scenario files, and model outputs that the user should be able to recreate using the model files in this archive.

A three-dimensional groundwater flow model, MODFLOW 6, was developed to provide a better understanding of the hydrogeology of the Harney Basin, southeastern Oregon. The model was used to investigate the historical groundwater-level decline and storage loss associated with anthropogenic groundwater demands. The model was calibrated to 1930 through 2018 conditions. This USGS data release contains all of the input and output files for the simulation described in the associated model documentation report (https://doi.org/10.3133/sir2023XXXX)

A three-dimensional groundwater flow model, MODFLOW 6, was developed to provide a better understanding of the hydrogeology of the Harney Basin, southeastern Oregon. The model was used to investigate the historical groundwater-level decline and storage loss associated with anthropogenic groundwater demands. The model was calibrated to 1930 through 2018 conditions. This USGS data release contains all of the input and output files for the simulation described in the associated model documentation report (https://doi.org/10.3133/sir2023XXXX)

A three-dimensional groundwater flow model, MODFLOW 6, was developed to provide a better understanding of the hydrogeology of the Harney Basin, southeastern Oregon. The model was used to investigate the historical groundwater-level decline and storage loss associated with anthropogenic groundwater demands. The model was calibrated to 1930 through 2018 conditions. This USGS data release contains all of the input and output files for the simulation described in the associated model documentation report (https://doi.org/10.3133/sir2023XXXX)

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).

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).