The U.S. Geological Survey, in cooperation with the National Park Service (NPS), developed a three-dimensional groundwater-flow model to simulate climate-change-related changes in depth to the water table and depth to freshwater/saltwater interfaces for the Fire Island National Seashore, New York. An existing SEAWAT three-dimensional variable-density groundwater flow and transport model (https://doi.org/10.3133/sir20095259) was converted to a MODFLOW–NWT three-dimensional finite-difference groundwater model with the Seawater Intrusion (SWI2) package and recalibrated using the UCODE_2005 automatic calibration software. A management goal for the Fire Island National Seashore is to increase the resiliency and capacity of coastal habitat and infrastructure to withstand storms and reduce the amount of damage caused by major storms. To facilitate management of ecohydrological effects and to increase understanding of the relation between sea-level rise and groundwater, as it relates to the ecology of the maritime forests and other vegetated areas on the island, the NPS requires hydrologic information. Accelerated sea-level rise, storms, rising temperatures, and changes in patterns of precipitation are all expected to drive considerable ecological changes. This model was used to evaluate three sea-level rise scenarios with 0.2-, 0.4-, and 0.6-meter increases above the 2015 level, applied to the existing topography. An additional high-recharge scenario, with the 0.6-meter increase, was created by increasing 2015 recharge rates by 10 percent. Understanding the possible effects of sea-level rise and changes in recharge on groundwater resources will allow the NPS to allocate scarce resources to best prepare for and manage climate-change-driven changes in the groundwater system and the subsequent effects on seashore ecosystems. 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/sir20205117).

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 (MODFLOW-NWT) was developed to examine groundwater storage changes in the Quincy Basin, Washington. The model was calibrated to conditions from 1920 to 2013. The model was used to (1) determine the change in groundwater storage from 1920 to 2013 , and (2) simulate the potential effects of increases in pumping, decrease in irrigation recharge, and increases in streamflow in Crab Creek by 100 cubic feet per second and 500 cubic feet per second. 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/sir20185162).

A three-dimensional, groundwater flow model (MODFLOW-NWT) was developed to examine groundwater storage changes in the Quincy Basin, Washington. The model was calibrated to conditions from 1920 to 2013. The model was used to (1) determine the change in groundwater storage from 1920 to 2013 , and (2) simulate the potential effects of increases in pumping, decrease in irrigation recharge, and increases in streamflow in Crab Creek by 100 cubic feet per second and 500 cubic feet per second. 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/sir20185162).

A three dimensional groundwater flow model (MODFLOW-NWT) was developed to examine the effects of changes to engineering controls and Lake Michigan surface water levels on the distribution of ponded water near Long Lake in Indiana Dunes National Lakeshore, near Gary, Indiana. The steady state model was calibrated to relatively low groundwater level condition of October 2002 and a relatively high groundwater level condition of March 2011. Scenario models were generated that examined the effects of (1) removing the beaver dams in US-12 ditch, (2) discontinuing seepage of water from the filtration pond east of East Long Lake, (3) discontinuing discharge from US-12 ditch to the Gary Sanitary District sewer system, (4) decreasing discharge from US-12 ditch to the Gary Sanitary District sewer system, (5) connecting East Long Lake and West Long Lake, (6) deepening County Line Road ditch, and (7) raising and lowering the water level of Lake Michigan. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://pubs.usgs.gov/sir/2013/5003/).

This groundwater-flow model archive contains all of the input and output files for an inset MODFLOW-NWT model extracted from the northern (Wisconsin) half of a published USGS steady-state regional model of the Upper Fox River Basin in the U.S. Upper Midwest. The construction and details of the published USGS steady-state model of the Upper Fox River Basin is outlined in the U.S. Geological Survey Scientific Investigations Report 2018-5038 (https://doi.org/10.3133/sir20185038). The regional model is archived in the data release at https://doi.org/10.5066/F76D5R5V. The extracted model was used to demonstrate an innovative new method for delinating fen distribution and discharge using the MODFLOW UZF package. The extracted model incorporates the Mukwonago River Basin, a 10-digit hydrologic unit code (HUC10) basin occupying 86.2 mi2 (223 km2) in southeastern Wisconsin. The extracted model was used to demonstrate how regional and local flow patterns can be enhanced by adding a version of the UZF file that automatically inserts “seepage drains” in cells where the water table is near the land surface (within the “undulation depth”). Details on the extracted model construction and calibration, including preparation of the “stripped-down” UZF file central to the proposed fen delineation method can be found in the supporting information of the journal article in Groundwater (https://doi.org/10.1111/gwat.12931). This USGS data release contains all of the input and output files for the simulations described in the journal article in Groundwater (https://doi.org/10.1111/gwat.12931).

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 with the SWI2 module, was developed to provide a better understanding of the fresh groundwater system of Assateague Island, Maryland and Virginia. Groundwater flow on Assateague Island was simulated to evaluate the effects of sea-level rise and changes in recharge on the depth to freshwater below the land surface, changes in freshwater discharge, and the depth of the freshwater/saltwater interface. The model was calibrated to average 2014-15 hydrologic conditions and vegetation. The model also simulated the movement of the freshwater- seawater interface for three sea-level rise scenarios.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/sir20205104).

The U.S. Geological Survey, in cooperation with Broward County Environmental Planning and Resilience Division, has developed a groundwater/surface-water model to evaluate the response of the drainage infrastructure and groundwater system in Broward County to increases in sea level and potential changes in precipitation. The model was constructed using a modified version of MODFLOW-NWT, with the surface-water system represented using the Surface-Water Routing process and the Urban Runoff Process. The surface-water drainage system within this newly developed model actively simulates the extensive canal network using level-pool routing and active structures representing gates, weirs, culverts, and pumps. Steady-state and transient simulation results represented historical conditions (2013-17). Simulation results incorporating increased sea level and precipitation were used to evaluate the effects on the surface-water drainage system and wet season groundwater levels. Four future sea-level scenarios were simulated by modifying the historical inputs for both the steady-state and the transient models to represent mean sea levels of 0.5, 2.0, 2.5, and 3.0 ft above the North American Vertical Datum of 1988. 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/sir20225074)

The U.S. Geological Survey, in cooperation with Broward County Environmental Planning and Resilience Division, has developed a groundwater/surface-water model to evaluate the response of the drainage infrastructure and groundwater system in Broward County to increases in sea level and potential changes in precipitation. The model was constructed using a modified version of MODFLOW-NWT, with the surface-water system represented using the Surface-Water Routing process and the Urban Runoff Process. The surface-water drainage system within this newly developed model actively simulates the extensive canal network using level-pool routing and active structures representing gates, weirs, culverts, and pumps. Steady-state and transient simulation results represented historical conditions (2013-17). Simulation results incorporating increased sea level and precipitation were used to evaluate the effects on the surface-water drainage system and wet season groundwater levels. Four future sea-level scenarios were simulated by modifying the historical inputs for both the steady-state and the transient models to represent mean sea levels of 0.5, 2.0, 2.5, and 3.0 ft above the North American Vertical Datum of 1988. 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/sir20225074)