A three-dimensional, groundwater flow model was developed with the numerical code MODFLOW-NWT to represent changes in groundwater pumping and aquifer recharge in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York to North Carolina. The model was constructed using existing hydrogeologic and geospatial information to represent the aquifer system geometry, boundaries, and hydraulic properties of the 19 separate regional aquifers and confining units within the aquifer system. The model was calibrated using an inverse modeling parameter-estimation (PEST) technique to conditions from 1986 to 2008, the period for which data are most complete and reliable. The simulation period for this analysis spanned from predevelopment to future conditions, from 1900 to 2058. The model was used to advance the understanding of groundwater budgets and components including recharge, discharge, and aquifer storage for the entire system and for each of the statewide systems; compute historical and recent system response and project future system response to development at a scale relevant to basinwide water-management decisions; and evaluate options for hydrologic monitoring of system changes. The report ‘Documentation of a groundwater flow model developed to assess groundwater availability in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to North Carolina: U.S. Geological Survey Scientific Investigations Report 2016–5076' (https://doi.org/10.3133/sir20165076) documents the model design and calibration, as well as several simulations to test model construction assumptions. The report 'Assessment of groundwater availability in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to North Carolina: U.S. Geological Survey Professional Paper 1829' (https://doi.org/10.3133/pp1829) documents water-availability simulations and the resulting analysis and discussion. This USGS data release contains all of the input and output files for the simulations described in the associated reports (https://doi.org/10.3133/sir20165076) and (https://doi.org/10.3133/pp1829). This data release also includes (1) MODFLOW-NWT source code, (2) the PEST files and source code used for model calibration, and (3) the ZONEBUDGET input files and source code used for the groundwater availability analysis.

A three-dimensional groundwater flow model (MODFLOW-NWT) of the Columbia Plateau Regional aquifer (CPRAS) in Washington, Oregon, and Idaho was developed to provide an integrated understanding of the hydrologic system to implement effective water-resource management strategies. The U.S. Geological Survey (USGS) Groundwater Resources Program assessed the groundwater availability as part of a national study of regional systems (https://pubs.usgs.gov/circ/1323/). The CPRAS assessment includes the status of groundwater resources, how these resources have changed over time, and development and application of tools to estimate system responses to stresses from future uses and climate variability and change. A major product of this assessment is a numerical groundwater-flow model of the system. Two models were constructed to simulate groundwater flow in the CPRAS: a steady-state predevelopment model representing conditions before large-scale pumping and irrigation altered the system, and a transient model representing the period 1900–2007. Construction of the model, development and calibration of the steady-state and transient simulations, as well as, a commingling scenario, is documented in the Scientific Investigations Report 2014-5127 (https://doi.org/10.3133/sir20145127). Two additional scenarios were completed and documented in the U.S. Geological Survey Professional Paper 1817 (https://doi.org/10.3133/pp1817). One scenario represents long-term equilibrium under 2007 conditions and the other modified the equilibrium conditions to account for potential increased pumpage under projected temperature increases with climate change. The model is a useful tool for investigating water supply, water demand, management strategies, groundwater-surface water exchanges, and potential effects of changing climate on the hydrologic system. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation reports: U.S. Geological Survey Professional Paper 1817 (https://doi.org/10.3133/pp1817) and the modeling report that documents the construction and calibration of the model, Scientific Investigations Report 2014-5127 (https://doi.org/10.3133/sir20145127).

A three-dimensional groundwater flow model (MODFLOW-NWT) of the Columbia Plateau Regional aquifer (CPRAS) in Washington, Oregon, and Idaho was developed to provide an integrated understanding of the hydrologic system to implement effective water-resource management strategies. The U.S. Geological Survey (USGS) Groundwater Resources Program assessed the groundwater availability as part of a national study of regional systems (https://pubs.usgs.gov/circ/1323/). The CPRAS assessment includes the status of groundwater resources, how these resources have changed over time, and development and application of tools to estimate system responses to stresses from future uses and climate variability and change. A major product of this assessment is a numerical groundwater-flow model of the system. Two models were constructed to simulate groundwater flow in the CPRAS: a steady-state predevelopment model representing conditions before large-scale pumping and irrigation altered the system, and a transient model representing the period 1900–2007. Construction of the model, development and calibration of the steady-state and transient simulations, as well as, a commingling scenario, is documented in the Scientific Investigations Report 2014-5127 (https://doi.org/10.3133/sir20145127). Two additional scenarios were completed and documented in the U.S. Geological Survey Professional Paper 1817 (https://doi.org/10.3133/pp1817). One scenario represents long-term equilibrium under 2007 conditions and the other modified the equilibrium conditions to account for potential increased pumpage under projected temperature increases with climate change. The model is a useful tool for investigating water supply, water demand, management strategies, groundwater-surface water exchanges, and potential effects of changing climate on the hydrologic system. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation reports: U.S. Geological Survey Professional Paper 1817 (https://doi.org/10.3133/pp1817) and the modeling report that documents the construction and calibration of the model, Scientific Investigations Report 2014-5127 (https://doi.org/10.3133/sir20145127).

In 2016, the United States Geological Survey (USGS) began development of a regional-scale numerical model of the Long Island aquifer system, as part of the National Water Quality Assessment (NAWQA) Program. The three-dimensional groundwater-flow model was developed to evaluate 1) responses of the hydrologic system to changes in natural and anthropogenic hydraulic stresses 2) the subsurface distribution of groundwater age, and 3) the regional-scale distribution of groundwater travel times and the source of water to fresh surface waters and coastal receiving waters. The model also provides the groundwater flow components used to define model boundaries for possible inset models used for local-scale analyses. Unconsolidated sediments underlying the Island comprise a sole source aquifer that supplies water to about 2.9 million people in Nassau and Suffolk Counties; the aquifer also contributes groundwater discharge to freshwater and marine ecosystems. Anthropogenic activities have affected both the quantity and quality of groundwater, owing to the Island's large population and the generally unconfined conditions prevalent across the aquifer system. Groundwater withdrawals, particularly in the western part of the Island, have resulted in large declines in water-table altitude and in the landward movement of the freshwater/saltwater interface encroaching on local water supplies. Subsurface contamination emanating from numerous point sources, often associated with industrial sites in developed areas in western Long Island, adversely affect downgradient water supplies. In central and eastern Long Island, nutrients emanating from non-point sources associated with residential development and agricultural activities have degraded water quality in shallow parts of the aquifer system. The model uses the numerical code MODFLOW-NWT to represent steady-state conditions for predevelopment and 2005-2015 average groundwater pumping and aquifer recharge. The particle-tracking algorithm MODPATH was used to simulate advective transport in the aquifer, to delineate the areas at the water table that contribute recharge to coastal and freshwater bodies, and to estimate total travel times of water from the water table to discharge locations. 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/sir20205091). UPDATE: In July 2021, the MODFLOW-NWT output for the steady-state 2005-2015 model were used with the particle-tracking algorithm MODPATH6 to estimate the recharge areas to 1,662 simulated public-supply wells in the aquifer system underlying Long Island, NY. An array of particles with a uniform spacing of 250 feet were specified at the water table and tracked forward to model cells containing simulated wells. The starting locations of the particles terminating in the simulated well represents the recharge area to that well. The particle starting locations were then georeferenced and used to create a polygon shapefile of individual recharge areas. This new information has been added to the ancillary directory of this data releases - December 2021.

A three-dimensional groundwater flow model was developed to characterize groundwater resources 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 is intended to be 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. The three-dimensional groundwater-flow model was developed using the numerical modeling software, MODFLOW-NWT. The steady-state (mean) hydrological conditions included data from 1981 to 2005, and transient (temporally-varying) conditions included a combination of a steady state period with data prior to 1960, and a transient period from 1961 to 2005. The model was calibrated by attempting to match simulated and measured or estimated hydraulic heads, differences in hydraulic heads between aquifers, stream base flow, and measured flow at flowing artesian wells. Sub-regional water budgets for the model area were produced with ZONEBUDGET. 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/sir201755158). This data release also includes (1) MODFLOW-NWT (version 1.0.9) source code, and (2) ZONEBUDGET source code.

A three-dimensional groundwater flow model was developed to characterize groundwater resources 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 is intended to be 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. The three-dimensional groundwater-flow model was developed using the numerical modeling software, MODFLOW-NWT. The steady-state (mean) hydrological conditions included data from 1981 to 2005, and transient (temporally-varying) conditions included a combination of a steady state period with data prior to 1960, and a transient period from 1961 to 2005. The model was calibrated by attempting to match simulated and measured or estimated hydraulic heads, differences in hydraulic heads between aquifers, stream base flow, and measured flow at flowing artesian wells. Sub-regional water budgets for the model area were produced with ZONEBUDGET. 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/sir201755158). This data release also includes (1) MODFLOW-NWT (version 1.0.9) source code, and (2) ZONEBUDGET source code.

In the Chenango River Basin, New York, glacial valley-fill unconfined and confined aquifers are an important source of drinking-water supplies. The U.S. Geological Survey developed three-dimensional groundwater-flow models (MODFLOW-NWT code) of three study areas in the basin to improve understanding of groundwater flow and delineate areas contributing recharge to 16 production wells as part of an effort to protect the source of water to these wells. The modeled areas were the Cortland study area in Cortland County (CCSA), Greene study area (GSA), and the Cincinnatus study area (CSA). Production wells in CCSA tap unconfined aquifers, whereas the production wells in GSA and CSA are screened in confined aquifers. The CCSA, which has an extensive calibration dataset, was calibrated by nonlinear regression and included a prediction uncertainty analysis. The GSA and CSA were manually calibrated because of the sparse model design and calibration information. The groundwater-flow models along with particle tracking (MODPATH code) were used to simulate water levels, base flows, water budgets, and flow paths. The USGS data release contains all the input and output files and source codes for the simulations described in the associated report: https//doi.org/10.3133/sir20215083.

In the Chenango River Basin, New York, glacial valley-fill unconfined and confined aquifers are an important source of drinking-water supplies. The U.S. Geological Survey developed three-dimensional groundwater-flow models (MODFLOW-NWT code) of three study areas in the basin to improve understanding of groundwater flow and delineate areas contributing recharge to 16 production wells as part of an effort to protect the source of water to these wells. The modeled areas were the Cortland study area in Cortland County (CCSA), Greene study area (GSA), and the Cincinnatus study area (CSA). Production wells in CCSA tap unconfined aquifers, whereas the production wells in GSA and CSA are screened in confined aquifers. The CCSA, which has an extensive calibration dataset, was calibrated by nonlinear regression and included a prediction uncertainty analysis. The GSA and CSA were manually calibrated because of the sparse model design and calibration information. The groundwater-flow models along with particle tracking (MODPATH code) were used to simulate water levels, base flows, water budgets, and flow paths. The USGS data release contains all the input and output files and source codes for the simulations described in the associated report: https//doi.org/10.3133/sir20215083.

A three-dimensional groundwater flow model was developed to simulate the effects of withdrawals on the groundwater-flow systems of five aquifers in and around Ocean County, New Jersey—the unconfined Kirkwood-Cohansey aquifer system and Vincentown aquifer, and three confined aquifers--the Rio Grande water-bearing zone, the Atlantic City 800-foot sand, and the Piney Point aquifer. A transient model was used to simulate conditions that represent no groundwater withdrawals, 2000–2003 groundwater withdrawals, and maximum-allocation groundwater withdrawals. Particle-tracking analysis, using results from two steady-state simulations, determine flow paths and travel times to near-shore wells screened in the unconfined Kirkwood-Cohansey aquifer system, the Rio Grande water-bearing zone, and the Atlantic City 800-foot sand. Sources of water to wells in both unconfined and confined aquifers and travel times based on particle-tracking analysis are used to assess the susceptibility of selected wells to saltwater intrusion from bay or ocean water. 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/sir20165035).

A three-dimensional groundwater flow model was developed to simulate the effects of withdrawals on the groundwater-flow systems of five aquifers in and around Ocean County, New Jersey—the unconfined Kirkwood-Cohansey aquifer system and Vincentown aquifer, and three confined aquifers--the Rio Grande water-bearing zone, the Atlantic City 800-foot sand, and the Piney Point aquifer. A transient model was used to simulate conditions that represent no groundwater withdrawals, 2000–2003 groundwater withdrawals, and maximum-allocation groundwater withdrawals. Particle-tracking analysis, using results from two steady-state simulations, determine flow paths and travel times to near-shore wells screened in the unconfined Kirkwood-Cohansey aquifer system, the Rio Grande water-bearing zone, and the Atlantic City 800-foot sand. Sources of water to wells in both unconfined and confined aquifers and travel times based on particle-tracking analysis are used to assess the susceptibility of selected wells to saltwater intrusion from bay or ocean water. 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/sir20165035).