A regional groundwater-flow model and particle-tracking program were used to delineate areas contributing groundwater to coastal and freshwater bodies and to estimate travel times from the water table to saline water bodies under average conditions from 1968 to 1983 on Long Island, New York. The coastal waters of Long Island are important economic and recreational resources for the region. The coastal water bodies receive freshwater from inflow of both surface water and groundwater, in addition to tidal exchanges of saltwater. Excessive nitrogen inputs associated with development and urbanization in the freshwater recharge areas to coastal water bodies can adversely affect marine and estuarine ecosystems. The results from this study will be beneficial for developing informed strategies to address nutrient loading to these systems, to provide a basis for additional scientific studies, and to engage the public. This is the first phase in the development of an updated groundwater-flow model for Long Island as part of the National Water Quality assessment Program (NAWQA). The study modified and used the model documented in the publication 'Simulation of the effects of development of the ground-water flow system of Long Island, New York by Herbert T. Buxton and Douglas A. Smolensky (https://pubs.er.usgs.gov/publication/wri984069). This data release contains all of the model input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20165138).

A regional groundwater-flow model and particle-tracking program were used to delineate areas contributing groundwater to coastal and freshwater bodies and to estimate travel times from the water table to saline water bodies under average conditions from 1968 to 1983 on Long Island, New York. The coastal waters of Long Island are important economic and recreational resources for the region. The coastal water bodies receive freshwater from inflow of both surface water and groundwater, in addition to tidal exchanges of saltwater. Excessive nitrogen inputs associated with development and urbanization in the freshwater recharge areas to coastal water bodies can adversely affect marine and estuarine ecosystems. The results from this study will be beneficial for developing informed strategies to address nutrient loading to these systems, to provide a basis for additional scientific studies, and to engage the public. This is the first phase in the development of an updated groundwater-flow model for Long Island as part of the National Water Quality assessment Program (NAWQA). The study modified and used the model documented in the publication 'Simulation of the effects of development of the ground-water flow system of Long Island, New York by Herbert T. Buxton and Douglas A. Smolensky (https://pubs.er.usgs.gov/publication/wri984069). This data release contains all of the model input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20165138).

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).

The U.S. Geological Survey (USGS), in cooperation with the Harris-Galveston Subsidence District and Fort Bend Subsidence District, constructed a finite-difference numerical groundwater-flow model of the northern Gulf Coast aquifer region for 1897 through 2018 using MODFLOW 6 with the Newton formulation solver to simulate groundwater flow and land-surface subsidence. Model parameter estimation and uncertainty analysis were conducted with PEST++ Iterative Ensemble Smoother software. The simulated results are described in the associated U.S. Geological Survey Professional Paper 1877. The model archive provided in this U.S. Geological Survey data release includes all the necessary files to run the MODFLOW 6 model and process the results for the posterior base realization as displayed in the accompanying report. The readme_v2.txt file describes selected files and directories in the archive and provides instructions for running the model. This 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/pp1877). This data release version 2.0 has been updated from the original version to include additional model outputs. The model inputs are identical to those included in data release version 1.0 and will produce identical results.

The U.S. Geological Survey (USGS), in cooperation with the Harris-Galveston Subsidence District and Fort Bend Subsidence District, constructed a finite-difference numerical groundwater-flow model of the northern Gulf Coast aquifer region for 1897 through 2018 using MODFLOW 6 with the Newton formulation solver to simulate groundwater flow and land-surface subsidence. Model parameter estimation and uncertainty analysis were conducted with PEST++ Iterative Ensemble Smoother software. The simulated results are described in the associated U.S. Geological Survey Professional Paper 1877. The model archive provided in this U.S. Geological Survey data release includes all the necessary files to run the MODFLOW 6 model and process the results for the posterior base realization as displayed in the accompanying report. The readme_v2.txt file describes selected files and directories in the archive and provides instructions for running the model. This 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/pp1877). This data release version 2.0 has been updated from the original version to include additional model outputs. The model inputs are identical to those included in data release version 1.0 and will produce identical results.

The U.S. Geological Survey (USGS), in cooperation with the Harris-Galveston Subsidence District and Fort Bend Subsidence District, constructed a finite-difference numerical groundwater-flow model of the northern Gulf Coast aquifer region for 1897 through 2018 using MODFLOW 6 with the Newton formulation solver to simulate groundwater flow and land-surface subsidence. Model parameter estimation and uncertainty analysis were conducted with PEST++ Iterative Ensemble Smoother software. The simulated results are described in the associated U.S. Geological Survey Professional Paper 1877. The model archive provided in this U.S. Geological Survey data release includes all the necessary files to run the MODFLOW 6 model and process the results for the posterior base realization as displayed in the accompanying report. The readme_v2.txt file describes selected files and directories in the archive and provides instructions for running the model. This 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/pp1877). This data release version 2.0 has been updated from the original version to include additional model outputs. The model inputs are identical to those included in data release version 1.0 and will produce identical results.

A three-dimensional groundwater flow model was developed to characterize groundwater resources of the uppermost principal aquifers in the Williston structural basin in parts of Montana, North Dakota, and South Dakota in the United States and of Manitoba and Saskatchewan in Canada as part of a detailed assessment of the groundwater availability of the area. The uppermost principal aquifers are comprised of the glacial, lower Tertiary, and Upper Cretaceous aquifer systems. The model was developed as a part of the U.S. Geological Survey Water Availability and Use Science Program's effort to conduct large-scale multidisciplinary regional studies of groundwater availability. The numerical model was used to (1) simulate hydrologic scenarios of interest to groundwater managers and to advance the understanding of groundwater budgets and components including recharge, discharge, and aquifer storage for the entire system, (2) compute historical and projected system response to natural and anthropogenic stresses, and (3) evaluate potential hydrologic monitoring programs at a scale relevant to basin-wide water-management decisions. This model was previously published by the U.S. Geological Survey in a Scientific Investigations Report (https://doi.org/10.3133/sir20175158) and the model input and output files are available in a data release (https://doi.org/10.5066/F75B01CZ). The underlying directories contain all of the input and output files for predictive simulations of groundwater response to selected scenarios for the uppermost principal aquifer systems in the Williston Basin, United States and Canada. The predictive simulations were created using base model files from a model developed by Davis and Long and documented in the U.S. Geological Survey Scientific Investigations Report 2017-5158 (https://doi.org/10.3133/sir20175158). Model archive files are documented and are available in an online data release (https://doi.org/10.5066/F75B01CZ). The three-dimensional groundwater-flow model was developed using the numerical modeling software, MODFLOW-NWT. For this study, the numerical groundwater-flow model was used to simulated three predictive scenarios: scenario 1 was focused on flowing artesian wells, and was used to simulate 1960‒2035 hydraulic-head changes that would result if none of the flowing artesian wells in the model area were capped or plugged during this period and other conditions remained constant; scenario 2 simulated 10-year drought for 2006‒15, with no increases in groundwater pumping after 2005; and scenario 3 was identical to scenario 2, except that it also applied the increased groundwater withdrawals necessary to fill the needs of energy-resource production for 2006‒15. A data-worth analysis for evaluation of potential hydrologic monitoring networks was also accomplished using the numerical model. This USGS data release contains all of the input and output files for the model described in the associated model documentation report (https://doi.org/10.3133/pp1841). This data release also includes MODFLOW-NWT (version 1.0.9) source code.

A three-dimensional groundwater flow model was developed to characterize groundwater resources of the uppermost principal aquifers in the Williston structural basin in parts of Montana, North Dakota, and South Dakota in the United States and of Manitoba and Saskatchewan in Canada as part of a detailed assessment of the groundwater availability of the area. The uppermost principal aquifers are comprised of the glacial, lower Tertiary, and Upper Cretaceous aquifer systems. The model was developed as a part of the U.S. Geological Survey Water Availability and Use Science Program's effort to conduct large-scale multidisciplinary regional studies of groundwater availability. The numerical model was used to (1) simulate hydrologic scenarios of interest to groundwater managers and to advance the understanding of groundwater budgets and components including recharge, discharge, and aquifer storage for the entire system, (2) compute historical and projected system response to natural and anthropogenic stresses, and (3) evaluate potential hydrologic monitoring programs at a scale relevant to basin-wide water-management decisions. This model was previously published by the U.S. Geological Survey in a Scientific Investigations Report (https://doi.org/10.3133/sir20175158) and the model input and output files are available in a data release (https://doi.org/10.5066/F75B01CZ). The underlying directories contain all of the input and output files for predictive simulations of groundwater response to selected scenarios for the uppermost principal aquifer systems in the Williston Basin, United States and Canada. The predictive simulations were created using base model files from a model developed by Davis and Long and documented in the U.S. Geological Survey Scientific Investigations Report 2017-5158 (https://doi.org/10.3133/sir20175158). Model archive files are documented and are available in an online data release (https://doi.org/10.5066/F75B01CZ). The three-dimensional groundwater-flow model was developed using the numerical modeling software, MODFLOW-NWT. For this study, the numerical groundwater-flow model was used to simulated three predictive scenarios: scenario 1 was focused on flowing artesian wells, and was used to simulate 1960‒2035 hydraulic-head changes that would result if none of the flowing artesian wells in the model area were capped or plugged during this period and other conditions remained constant; scenario 2 simulated 10-year drought for 2006‒15, with no increases in groundwater pumping after 2005; and scenario 3 was identical to scenario 2, except that it also applied the increased groundwater withdrawals necessary to fill the needs of energy-resource production for 2006‒15. A data-worth analysis for evaluation of potential hydrologic monitoring networks was also accomplished using the numerical model. This USGS data release contains all of the input and output files for the model described in the associated model documentation report (https://doi.org/10.3133/pp1841). This data release also includes MODFLOW-NWT (version 1.0.9) source code.

This data release contains the input, output, and model code used to run a transient simulation of a previously published (Walter and others, 2020) steady-state regional model of Long Island, N.Y. The original model code was updated to MODFLOW 6 (version 6.3.0) and incorporates monthly transient stress periods to simulate conditions from 2005-2019 following methods described in Walter and others (2020). Selected remedial stresses (groundwater extraction and return) were incorporated for select locations in southeastern Nassau County. No modifications were made to the hydrologic boundaries, model layers, or hydraulic properties specified in the original model. A uniform value of 0.25 was used to represent specific yield (unconfined storage) and a uniform value of 0.00001 was used to represent specific storage (confined storage) which are typical values for Long Island sediments. Monthly values for natural recharge from precipitation were calculated using a Soil-Water Balance model (Finkelstein and others, 2022). Components of anthropogenic recharge--wastewater return flow, storm water inflow, and inflow from leaky infrastructure--were estimated for monthly stress periods consistent with the methods described in Walter and others (2020). Monthly groundwater withdrawals for various sources, including public-water supply, industrial, remediation, and agricultural, were compiled or estimated for the same period. No additional calibration was conducted for this scenario and as such, it is possible that in some locations the model simulation results may not accurately represent the temporal responses to monthly hydrologic stresses.

This data release contains the input, output, and model code used to run a transient simulation of a previously published (Walter and others, 2020) steady-state regional model of Long Island, N.Y. The original model code was updated to MODFLOW 6 (version 6.3.0) and incorporates monthly transient stress periods to simulate conditions from 2005-2019 following methods described in Walter and others (2020). Selected remedial stresses (groundwater extraction and return) were incorporated for select locations in southeastern Nassau County. No modifications were made to the hydrologic boundaries, model layers, or hydraulic properties specified in the original model. A uniform value of 0.25 was used to represent specific yield (unconfined storage) and a uniform value of 0.00001 was used to represent specific storage (confined storage) which are typical values for Long Island sediments. Monthly values for natural recharge from precipitation were calculated using a Soil-Water Balance model (Finkelstein and others, 2022). Components of anthropogenic recharge--wastewater return flow, storm water inflow, and inflow from leaky infrastructure--were estimated for monthly stress periods consistent with the methods described in Walter and others (2020). Monthly groundwater withdrawals for various sources, including public-water supply, industrial, remediation, and agricultural, were compiled or estimated for the same period. No additional calibration was conducted for this scenario and as such, it is possible that in some locations the model simulation results may not accurately represent the temporal responses to monthly hydrologic stresses.