As part of the National Water Census program in the Apalachicola-Chattahoochee-Flint (ACF) River Basin, the U.S. Geological Survey evaluated the groundwater budget of the lower ACF, with particular emphasis on recharge, characterizing the spatial and temporal relation between surface water and groundwater, and groundwater pumping. To evaluate the hydrologic budget of the lower ACF River Basin, a groundwater-flow model, constructed using MODFLOW-2005, was developed for the Upper Floridan aquifer and overlying semiconfining unit for 2008–12. Model input included temporally and spatially variable specified recharge, estimated using a preliminary version of a Precipitation-Runoff Modeling System (PRMS) model for the ACF River Basin, and pumping, partly estimated on the basis of measured agricultural pumping rates in Georgia. The model was calibrated to measured groundwater levels, and base flows which were estimated using hydrograph separation. The simulated groundwater flow budget resulted in a net cumulative loss in groundwater storage during the study period. Spatial variability in simulated hydrologic budgets for eight subbasins was attributed to such factors as soil storage capacity, Lake Seminole impoundment, and the presence of in-channel springs. The model simulated a net storage loss for all the subbasins. The model is limited by its conceptualization, the data used to represent and calibrate the model, and the mathematical representation of the system; therefore, any interpretations should be considered in light of these limitations. In spite of these limitations, the model provides insight regarding water availability in the lower ACF River Basin. 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/sir20175141).

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).

A revised regional groundwater-flow model using a modified grid in conjunction with USGS MODFLOW-2000 was developed to the predict the effects of Lower Floridan aquifer (LFA) groundwater pumpage on the Upper Floridan aquifer (UFA) in the Barbour Pointe community, Chatham County, Georgia. The model was modified using hydrogeologic information obtained from field investigations at Barbour Pointe, Berwick Plantation near Berwick, Pooler, Hunter Army Airfield, Rincon, and Fort Stewart.

A revised regional groundwater-flow model using a modified grid in conjunction with USGS MODFLOW-2000 was developed to the predict the effects of Lower Floridan aquifer (LFA) groundwater pumpage on the Upper Floridan aquifer (UFA) in the Barbour Pointe community, Chatham County, Georgia. The model was modified using hydrogeologic information obtained from field investigations at Barbour Pointe, Berwick Plantation near Berwick, Pooler, Hunter Army Airfield, Rincon, and Fort Stewart.

A simple water budget includes precipitation, streamflow, change in storage, evapotranspiration, and residuals: P=Q + ET + ΔS + e. It is essential to include the managed component (i.e., the “human” component) to close the water budget and reduce the magnitude of the residuals from “natural” water budgets. Some of the largest components of managed water withdraws are public supply, irrigation, and thermoelectric. The modified water budget is: P=Q + ET + ΔS + (PS + Irr + TE) + e, where PS is public supply, Irr is irrigation, and TE is thermoelectric water use. This data release contains both the natural and managed components of the water budget for a region within the Apalachicola-Chattahoochee-Flint (ACF) River Basin, GA, U.S. The natural components include precipitation, evapotranspiration, and discharge and the managed components include public supply, irrigation, and thermoelectric. This table contains HUC 10 IDs, year, the natural components of the water budget, and water-use data aggregated from sites to HUC 10s for the years 2008–2012.

A simple water budget includes precipitation, streamflow, change in storage, evapotranspiration, and residuals: P=Q + ET + ΔS + e. It is essential to include the managed component (i.e., the “human” component) to close the water budget and reduce the magnitude of the residuals from “natural” water budgets. Some of the largest components of managed water withdraws are public supply, irrigation, and thermoelectric. The modified water budget is: P=Q + ET + ΔS + (PS + Irr + TE) + e, where PS is public supply, Irr is irrigation, and TE is thermoelectric water use. This data release contains both the natural and managed components of the water budget for a region within the Apalachicola-Chattahoochee-Flint (ACF) River Basin, GA, U.S. The natural components include precipitation, evapotranspiration, and discharge and the managed components include public supply, irrigation, and thermoelectric. This table contains HUC 10 IDs, year, the natural components of the water budget, and water-use data aggregated from sites to HUC 10s for the years 2008–2012.

The U.S. Geological Survey, in cooperation with the Southwest Florida Water Management District, calibrated a model to quantify the inflows and outflows in the Floral City, Inverness, and Hernando pools of the Tsala Apopka Lake basin in Citrus County, Florida. The calibrated model, which uses MODFLOW-NWT version 1.1.2, simulates hydrologic changes in pool stages, groundwater levels, spring flows, and streamflows caused by the diversion of streamflow from the Withlacoochee River to the Tsala Apopka Lake basin through water-control structures. A surface-water/groundwater flow model was developed using hydraulic parameters for lakes, streams, the unsaturated zone, and the underlying surficial and Upper Floridan aquifers estimated with an inverse modeling calibration technique. After calibration, the model was used to assess the relation between inflows and outflows in the Tsala Apopka Lake basin and changes in pool stages. Simulation results using the calibrated surface-water/groundwater flow model showed that the largest leakage rates from the pools to the Upper Floridan aquifer occurred at the deep lake cells and that these leakage rates were higher than any recharge rates to the Upper Floridan aquifer in the model area. There was downward leakage to the Upper Floridan aquifer in most of the Floral City, Inverness, and Hernando pools. The calibrated surface-water and groundwater flow model was used to simulate hydrologic scenarios that included: small changes in rainfall rates, projected increases in groundwater pumping rates for 2025 and 2035, no flow for the entire period through the eight water-control structures in the Tsala Apopka Lake basin, and the removal of the Inglis Dam and the Inglis Bypass Spillway on Lake Rousseau. 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/sir20185055).

The U.S. Geological Survey, in cooperation with the Southwest Florida Water Management District, calibrated a model to quantify the inflows and outflows in the Floral City, Inverness, and Hernando pools of the Tsala Apopka Lake basin in Citrus County, Florida. The calibrated model, which uses MODFLOW-NWT version 1.1.2, simulates hydrologic changes in pool stages, groundwater levels, spring flows, and streamflows caused by the diversion of streamflow from the Withlacoochee River to the Tsala Apopka Lake basin through water-control structures. A surface-water/groundwater flow model was developed using hydraulic parameters for lakes, streams, the unsaturated zone, and the underlying surficial and Upper Floridan aquifers estimated with an inverse modeling calibration technique. After calibration, the model was used to assess the relation between inflows and outflows in the Tsala Apopka Lake basin and changes in pool stages. Simulation results using the calibrated surface-water/groundwater flow model showed that the largest leakage rates from the pools to the Upper Floridan aquifer occurred at the deep lake cells and that these leakage rates were higher than any recharge rates to the Upper Floridan aquifer in the model area. There was downward leakage to the Upper Floridan aquifer in most of the Floral City, Inverness, and Hernando pools. The calibrated surface-water and groundwater flow model was used to simulate hydrologic scenarios that included: small changes in rainfall rates, projected increases in groundwater pumping rates for 2025 and 2035, no flow for the entire period through the eight water-control structures in the Tsala Apopka Lake basin, and the removal of the Inglis Dam and the Inglis Bypass Spillway on Lake Rousseau. 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/sir20185055).

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).