As part of the Coastal Carolinas Focus Area Study of the U.S. Geological Survey National Water Census Program, the Soil and Water Assessment Tool (SWAT) was used to develop models for the Cape Fear River Basin, North Carolina, to simulate future streamflow and irrigation demand based on land use, climate, and water demand projections. SWAT is a basin-scale, process-based watershed model with the capability of simulating water-management scenarios. Model basins were divided into approximately two-square mile subbasins and subsequently divided into smaller, discrete hydrologic response units based on land use, slope, and soil type. The calibration period for the historic model was 2000 to 2014. The best available data on water-use from this time period were used, including public water supply, industrial water use, irrigation needs and golf courses. Six future scenario models simulated streamflow during the period 2055 to 2065 based on incorporation of two alternative land use projections, an ensemble of three global climate models, and water demand forecasts. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20235036).

As part of the Coastal Carolinas Focus Area Study of the U.S. Geological Survey National Water Census Program, the Soil and Water Assessment Tool (SWAT) was used to develop models for the Pee Dee River Basin, North Carolina and South Carolina, to simulate future streamflow and irrigation demand based on land use, climate, and water demand projections. SWAT is a basin-scale, process-based watershed model with the capability of simulating water-management scenarios. Model basins were divided into approximately two-square mile subbasins and subsequently divided into smaller, discrete hydrologic response units based on land use, slope, and soil type. The calibration period for the historic model was 2000 to 2014. The best available data on water-use from this time period were used, including public water supply, industrial water use, irrigation needs and golf courses. Six future scenario models simulated streamflow during the period 2055 to 2065 based on incorporation of two alternative land use projections, an ensemble of three global climate models, and water demand forecasts. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20235036).

As part of the Coastal Carolinas Focus Area Study of the U.S. Geological Survey National Water Census Program, the Soil and Water Assessment Tool (SWAT) was used to develop models for the Pee Dee River Basin, North Carolina and South Carolina, to simulate future streamflow and irrigation demand based on land use, climate, and water demand projections. SWAT is a basin-scale, process-based watershed model with the capability of simulating water-management scenarios. Model basins were divided into approximately two-square mile subbasins and subsequently divided into smaller, discrete hydrologic response units based on land use, slope, and soil type. The calibration period for the historic model was 2000 to 2014. The best available data on water-use from this time period were used, including public water supply, industrial water use, irrigation needs and golf courses. Six future scenario models simulated streamflow during the period 2055 to 2065 based on incorporation of two alternative land use projections, an ensemble of three global climate models, and water demand forecasts. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20235036).

Three groundwater flow models, using MODFLOW-2000, SEAWAT, and SHARP model codes, were used to evaluate plans to supply potable and non-potable water to residents and businesses of Cape May County, New Jersey until at least 2050. The ideal plan would meet projected demands and minimize adverse effects on currently used sources of potable, non- potable, and ecological water supplies. The U.S. Geological Survey used two previously developed groundwater flow models, as well as a newly developed groundwater flow model, to evaluate the shallow and deep aquifer systems in Cape May County. The groundwater flow in the shallow and deep aquifer systems of Cape May County were simulated separately. Flow in the shallow aquifers was simulated with a newly developed small-cell- size numerical model extending to the hydrologic boundaries. The saltwater transport modeling code, SEAWAT, was used to model the shallow system because of the accurate treatment of variable-density groundwater (saltwater front) and surface-water boundary (ecological-water supply) conditions. Flow in the deep aquifers was simulated using MODFLOW-2000 with a previously developed medium-cell-size numerical model encompassing Cape May County. This sub-regional groundwater-flow model (CMAC) was originally developed by Voronin (https://doi.org/10.3133/wri954280) to simulate advective flow in the Atlantic City 800-foot sand from the estimated 250-mg/L isochlor toward Stone Harbor. For this study, the CMAC model was revised to include the Rio Grande water-bearing zone and recalibrated with recent (2003) withdrawal data and water-level measurements. Boundary flows to the CMAC model were provided from the New Jersey Coastal Plain regional model (NJCP SHARP) (https://doi.org/10.3133/wri984216). This coarse-cell-size Coastal Plain-wide model uses the SHARP model code and simulates saltwater movement by treating the transition from freshwater to saltwater as a sharp interface, and therefore, only predicts large-scale movements of the 10,000-mg/L isochlor. To predict the effects of future actions on the water supplies, three baseline and six future scenarios were created and simulated with these three models. Depending on the scenario, proposed production wells would be installed in locations far from the saltwater fronts, in deep freshwater aquifers, in deeper saltwater aquifers, or proposed injection wells would be installed to inject reused water to create a freshwater barrier to saltwater intrusion. Particle- tracking was used with the CMAC model to estimate groundwater-flow paths and travel time from the location of the 250-mg/L isochlor to production wells or hypothetical production wells. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20095187).

Three groundwater flow models, using MODFLOW-2000, SEAWAT, and SHARP model codes, were used to evaluate plans to supply potable and non-potable water to residents and businesses of Cape May County, New Jersey until at least 2050. The ideal plan would meet projected demands and minimize adverse effects on currently used sources of potable, non- potable, and ecological water supplies. The U.S. Geological Survey used two previously developed groundwater flow models, as well as a newly developed groundwater flow model, to evaluate the shallow and deep aquifer systems in Cape May County. The groundwater flow in the shallow and deep aquifer systems of Cape May County were simulated separately. Flow in the shallow aquifers was simulated with a newly developed small-cell- size numerical model extending to the hydrologic boundaries. The saltwater transport modeling code, SEAWAT, was used to model the shallow system because of the accurate treatment of variable-density groundwater (saltwater front) and surface-water boundary (ecological-water supply) conditions. Flow in the deep aquifers was simulated using MODFLOW-2000 with a previously developed medium-cell-size numerical model encompassing Cape May County. This sub-regional groundwater-flow model (CMAC) was originally developed by Voronin (https://doi.org/10.3133/wri954280) to simulate advective flow in the Atlantic City 800-foot sand from the estimated 250-mg/L isochlor toward Stone Harbor. For this study, the CMAC model was revised to include the Rio Grande water-bearing zone and recalibrated with recent (2003) withdrawal data and water-level measurements. Boundary flows to the CMAC model were provided from the New Jersey Coastal Plain regional model (NJCP SHARP) (https://doi.org/10.3133/wri984216). This coarse-cell-size Coastal Plain-wide model uses the SHARP model code and simulates saltwater movement by treating the transition from freshwater to saltwater as a sharp interface, and therefore, only predicts large-scale movements of the 10,000-mg/L isochlor. To predict the effects of future actions on the water supplies, three baseline and six future scenarios were created and simulated with these three models. Depending on the scenario, proposed production wells would be installed in locations far from the saltwater fronts, in deep freshwater aquifers, in deeper saltwater aquifers, or proposed injection wells would be installed to inject reused water to create a freshwater barrier to saltwater intrusion. Particle- tracking was used with the CMAC model to estimate groundwater-flow paths and travel time from the location of the 250-mg/L isochlor to production wells or hypothetical production wells. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20095187).

Three existing groundwater flow models, using MODFLOW-2000, SEAWAT, and SHARP model codes, were used by the U.S. Geological Survey (USGS) to determine the effects of increased withdrawals, and shifts of withdrawals between 2 aquifers, on the limited water resources in the Cape May County, New Jersey. Saltwater intrusion and declining water levels have been a water-supply problem in Cape May County for decades. Several communities in the county have only one aquifer from which freshwater withdrawals can be made, and that sole source is threatened by saltwater intrusion and (or) substantial declines in water levels caused by groundwater withdrawals. Growth of the year-around and summer tourism populations have caused water demand for some purveyors to approach full-allocation withdrawal rates leading these purveyors to request increases in allocations. The three groundwater flow models were used to evaluate the shallow and deep aquifer systems of Cape May County. The groundwater flow in the shallow and deep aquifer systems were simulated separately. The lateral hydrologic boundaries of the shallow aquifer system generally coincide with the political boundary of Cape May County, whereas the boundaries for the deep aquifer system extend well beyond the county boundaries. Flow in the shallow aquifers was simulated with the saltwater-transport modeling code, SEAWAT. Flow in the deep aquifers was simulated using MODFLOW-2000 with a medium-cell-size numerical model (CMAC) encompassing Cape May County (https://doi.org/10.3133/wri954280) that was revised to include the Rio Grande water-bearing zone and recalibrated with recent (2003) withdrawal data and water-level measurements for a previous study of the Cape May County water resources (https://doi.org/10.3133/sir20095187). Boundary flows to the CMAC model were provided from the New Jersey Coastal Plain regional model (NJCP SHARP) (https://doi.org/10.3133/wri984216). This coarse-cell-size Coastal Plain-wide model uses the SHARP model code and simulates saltwater movement by treating the transition from freshwater to saltwater as a sharp interface, and therefore, only predicts large-scale movements of the 10,000-mg/L isochlor. Future groundwater withdrawal scenarios for the shallow and deep system were compared to baseline scenarios in an effort to balance the need for additional water with protection of the limited water resources in the county. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205052)

Three existing groundwater flow models, using MODFLOW-2000, SEAWAT, and SHARP model codes, were used by the U.S. Geological Survey (USGS) to determine the effects of increased withdrawals, and shifts of withdrawals between 2 aquifers, on the limited water resources in the Cape May County, New Jersey. Saltwater intrusion and declining water levels have been a water-supply problem in Cape May County for decades. Several communities in the county have only one aquifer from which freshwater withdrawals can be made, and that sole source is threatened by saltwater intrusion and (or) substantial declines in water levels caused by groundwater withdrawals. Growth of the year-around and summer tourism populations have caused water demand for some purveyors to approach full-allocation withdrawal rates leading these purveyors to request increases in allocations. The three groundwater flow models were used to evaluate the shallow and deep aquifer systems of Cape May County. The groundwater flow in the shallow and deep aquifer systems were simulated separately. The lateral hydrologic boundaries of the shallow aquifer system generally coincide with the political boundary of Cape May County, whereas the boundaries for the deep aquifer system extend well beyond the county boundaries. Flow in the shallow aquifers was simulated with the saltwater-transport modeling code, SEAWAT. Flow in the deep aquifers was simulated using MODFLOW-2000 with a medium-cell-size numerical model (CMAC) encompassing Cape May County (https://doi.org/10.3133/wri954280) that was revised to include the Rio Grande water-bearing zone and recalibrated with recent (2003) withdrawal data and water-level measurements for a previous study of the Cape May County water resources (https://doi.org/10.3133/sir20095187). Boundary flows to the CMAC model were provided from the New Jersey Coastal Plain regional model (NJCP SHARP) (https://doi.org/10.3133/wri984216). This coarse-cell-size Coastal Plain-wide model uses the SHARP model code and simulates saltwater movement by treating the transition from freshwater to saltwater as a sharp interface, and therefore, only predicts large-scale movements of the 10,000-mg/L isochlor. Future groundwater withdrawal scenarios for the shallow and deep system were compared to baseline scenarios in an effort to balance the need for additional water with protection of the limited water resources in the county. This USGS data release contains all the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20205052)

The U.S. Geological Survey, in cooperation with the Town of Barnstable, Massachusetts, modified an existing numerical, steady-state regional MODFLOW-2005 groundwater-flow model to evaluate changes in water levels from a reference condition (2015) for nine pumping and wastewater return flow scenarios prepared by the Hyannis Water System. The three-dimensional, steady-state groundwater-flow model used to simulate water level changes is a modified and recalibrated version of an existing model that was used to simulate the potential effects of sea-level rise on groundwater levels of the Sagamore and Monomoy freshwater lenses of the Cape Cod aquifer (Walter and others, 2016) (https://doi.org/10.3133/sir20165058). Two modifications, (1) the addition of spatially variable natural recharge from precipitation, and (2) a revised representation of wastewater return-flow recharge to septic systems in the Town of Barnstable, were made to the existing regional groundwater-flow model for this study. The modified model was recalibrated to the same observations of heads and streamflows as those used in the original model. The modifications and results of the recalibration are described in the appendix of the associated scientific investigations report (https://doi.org/10.3133/sir20195121). The model is a mathematical representation of the groundwater-flow system. Several assumptions and limitations of the modeling approach are discussed in the report, as well as in the scientific investigations report describing the original model (https://doi.org/10.3133/sir20165058). This USGS data release contains all the input and output files for the simulations described in the associated scientific investigations report (https://doi.org/10.3133/sir20195121). The modified model supersedes the original model described by Walter and others (https://doi.org/10.3133/sir20165058).

The U.S. Geological Survey (USGS), in cooperation with the Town of Falmouth, used an existing groundwater flow model to simulate responses of the freshwater hydrologic system in Falmouth, Massachusetts to proposed wastewater-return-flow scenarios. The existing model is a steady-state, three-dimensional MODFLOW-2005 model of the Sagamore flow lens of the Cape Cod aquifer documented by Walter and others (2019). The existing model was updated with groundwater withdrawal and wastewater-return-flow data to represent average conditions for calendar years 2019 through 2023. The updated model was then used to simulate two wastewater-return-flow scenarios associated with the potential installation of an ocean outfall pipe in Falmouth, Massachusetts. This USGS data release contains the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20255066). Associated Scientific Investigations Report: -------------------------------------- Goldstein, K.M.F., and McCobb, T.D., 2025, Simulated hydrologic responses to proposed wastewater-return-flow scenarios in Falmouth, Massachusetts: U.S. Geological Survey Scientific Investigations Report 2025-5066, 19 p., https://doi.org/10.3133/sir2025-5066. References: -------------------------------------- Walter, D.A., McCobb, T.D., and Fienen, M.N., 2019, Use of a numerical model to simulate the hydrologic system and transport of contaminants near Joint Base Cape Cod, Western Cape Cod, Massachusetts: U.S. Geological Survey Scientific Investigations Report 2019-5139, 98 p., https://doi.org/10.3133/sir20185139.

A previously developed model (https://doi.org/10.3133/sir20175098) was coupled with downscaled climate model data to determine the impact of climate variability on base flow and groundwater storage in the North Fork Red River aquifer, Oklahoma. The North Fork Red River aquifer is an alluvial aquifer that discharges groundwater to the North Fork Red River, which provides inflow to Lake Altus, an important water source for the surrounding communities. The impact of climate variability on hydrologic systems and the resulting effects on basins has become an important topic in assessing future water resources. Global climate projections from general circulation models, including the Coupled Model Intercomparison Project Phase 5 (CMIP5), have been developed to improve the understanding of climate science and forecast future climatic conditions. Due to the impact of climate variations on groundwater resources, it is important to communicate the ranges of results with water resource managers. To approximate a range in future base flow conditions and flow into Lake Altus, the Coupled Model Intercomparison Project Phase 5 climate data was downscaled to watershed scale using monthly Bias-Correction Spatial Disaggregation techniques. A time-series of scaling factors were developed and interpolated for three climate scenarios (central tendency, warmer/drier, and less warm-wetter) representing a range of future climate conditions for the period 2045–2074. These scaling factors were then applied to an existing soil-water-balance model dataset with climate data for the baseline period 1980–2009 to produce recharge and evapotranspiration estimations for this future period. The downscaled climate data was applied to the finite-difference numerical groundwater-flow model of the North Fork Red River aquifer using MODFLOW-2005 with the Newton formulation solver (MODFLOW-NWT) which was temporally discretized into 373 monthly transient stress periods representing the period 1980–2010. Three climate scenarios (central tendency, warmer/drier, and less warm/wetter) representing a range of future climate conditions for the period 2045–2074 were simulated. This USGS data release contains all of the input and output files for the simulations described in the associated journal article (http://doi.org/10.1007/s10040-020-02230-x).