A previously developed three-dimensional groundwater-flow model that used the MODFLOW-NWT code was updated to simulate the effects of various proposed drainage modifications aimed at reducing discharge to a sanitary sewer system near Long Lake in Indiana Dunes National Lakeshore, near Gary, Indiana. The original steady-state model documented in the USGS report (https://pubs.usgs.gov/sir/2013/5003/) and data release (https://doi.org/10.5066/F7D21VS2) was calibrated to a low groundwater level/dry weather condition of October 2002 and a high groundwater level/wet weather condition of March 2011. For this study the 2002 and 2011 simulations were updated with elevation data collected from a 2017 survey of primary surface-water features that affect groundwater levels to create dry- or wet-weather “base” simulations (figs. 1 and 2). Eight scenario models were created by modifying the updated 2002 and 2011 base simulations. The scenarios examined the effects of potential modifications to the hydrologic system: (scenario 1a) diverting water from US-12 weir (site CS-1) to County Line Road ditch through underground pipes [figs. 3-6], (scenario 1b) diverting water from US-12 ditch to Spencer ditch, then trenching Spencer ditch to the County Line Road ditch to drain to the Little Calumet River [figs. 7 and 8], (scenario 2) Extending and altering US-12 ditch to flow east toward County Line Road ditch and drain to the Little Calumet River [figs. 9 and 10], and (scenario 3) installing culverts under US-12 and adjacent railroad lines to connect US-12 ditch with West Long Lake [figs. 11-14]. This data release contains all files and associated information needed to run these additional simulations.

Changes in water-table position for each scenario simulation are categorized in figures in this data release as (1) within 7 feet of the land surface, (2) within 3 feet of the land surface, or (3) above land surface and are expressed relative to the water-table position simulated in the updated dry- or wet-weather base simulations. The descriptions focus primarily on changes to the distribution of groundwater towards the center of the model domain. Groundwater distributions towards the western edge (west of Grand Blvd.), southwest (south of US-20), and eastern edge (towards Ogden Dunes) of model domain show relatively small variations in the scenario simulations and are outside of the primary area of interest.

The scenario of rerouting water from entry into the Gary sanitary sewer system at the weir at site CS-1 to County Line Road ditch through underground pipes (scenario 1a; figs. 3-6) used the MODFLOW Drain Return Package to transmit water from the US-12 ditch to a drain return cell at the intersection of County Line Road ditch and 5th Avenue. This simulated hydrologic modification produced an expanded area of shallow groundwater within 7 feet of the land surface in the areas surrounding the drain return cell location. A small groundwater mound developed in the dry-weather underground pipes simulation at the intersection of County Line Road and 5th Avenue, with the water table within 3 feet of the land surface. In the dry-weather underground pipes simulation (figs. 3 and 4), the portions of the area between Union Street and County Line Road ditch were inundated. Water-table position changes north of US-12 or west of Spencer Street were minimal. In the wet-weather underground pipes simulation (figs. 5 and 6), water ponded at the intersection of County Line Road and East 5th Avenue. Both dry- and wet-weather underground pipes simulations exhibited similar patterns of water-table changes, but differences between water-table positions in the underground pipes and updated wet-weather base simulations were minimal in areas away from the drain return cell.

The scenario of diverting water from US-12 ditch to Spencer ditch then trenching to the County Line Road ditch (scenario 1b; figs. 7 and 8) required creation of new drain cells to connect the southern terminus of Spencer ditch to County Line Road ditch at 5th Avenue. These new drain cells were assigned bottom elevations derived from the 2017 ditch elevation survey. The simulated diversion and trench decreased the water table throughout the model domain, particularly in the area south of East 4th Avenue, where expansive areas of shallow groundwater were nearly eliminated. Between Spencer ditch and Union Street, the area of groundwater within 7 feet of the land surface was reduced in both dry- and wet-weather diversion and trench simulations. In most of the area just south of US-12 ditch between the US-12 weir (CS-1) and Union Street, the water table was suppressed to more than 3 feet below the land surface in both scenario simulations. In the wet-weather diversion and trench simulation, flooded areas south of US-12 and west of County Line Road ditch were minimized and changes to the water-table position north of US-12 or east of County Line Road ditch were minimal.

The scenario of extending and altering US-12 ditch to flow east towards County Line Road ditch and drain to the Little Calumet River (scenario 2; figs. 9 and 10) required creation of drain cells to connect the two ditches. New drain cells were assigned bottom elevations derived from the 2017 ditch elevation survey which intersected the simulated water table of the updated dry- and wet-weather base simulations. The result from the extended US-12 ditch simulation was a suppression of the water table throughout the model domain, with a pronounced reduction of shallow groundwater between Union Street and County Line Road ditch. In the dry-weather scenario simulation, the occurrence of ponded water was virtually eliminated in the area of interest, while areas simulated to have a water table within 3 feet of the land surface were highly reduced, generally only occurring near West Long Lake, East Long Lake, and along some parts of US-12 ditch. Between Spencer Street and Union Street, there were only limited areas with a water table within 7 feet of the land surface. In the wet-weather scenario simulation, groundwater altitudes were sufficiently suppressed as to eliminate nearly all of the inundated areas west of County Line Road and east of Spencer Street (including most of the areas surrounding West Long Lake).

The scenario simulating the installation of a culvert under US-12 to connect US-12 ditch to West Long Lake (scenario 3; figs. 11-14) utilized MODFLOW’s Drain Return Package to transmit water removed by the US-12 ditch to a drain return cell in the lake just north of the US-12 and Spencer Street intersection. The general effect of this scenario was a substantial increase in water-table altitude throughout the model domain, particularly north of US-12. In the dry-weather culvert scenario simulation, the West Long Lake basin defined as the vacant area enclosed by US-12 to the south, County Line Road to the east, and Gary neighborhoods to the north was nearly completely inundated. Several areas of ponded water also developed between Union Street and County Line Road Ditch. In both the dry- and wet-weather culvert scenario simulations, shallow groundwater extended north from the West Long Lake basin into nearby Gary residential areas. Some isolated areas of ponded water were simulated in the area north from the lake to Lake Michigan in the wet-weather culvert scenario simulation. East of County Line Road ditch, water-table altitudes increased slightly in both dry- and wet-weather culvert scenario simulations but the extent of shallow groundwater did not change or substantially expand when compared with the updated wet-weather base simulation. Limited water-table position changes were depicted west of Union Street and south of US-12 ditch in both dry- and wet-weather culvert scenario simulations.