MODFLOW-NWT model scenarios used to evaluate potential effects of proposed drainage modifications on groundwater discharge in the vicinity of Long Lake, Indiana Dunes National Lakeshore, near Gary, Indiana

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.

Tags: calumet-aquifer, environment, geoscientificinformation, great-lakes, groundwater, groundwater-flow-modeling, groundwater-model, indiana, indiana-dunes, inlandwaters, lake-michigan, modflow-nwt, national-park-service, nps, usgs-f15061cf-4404-484c-8897-4fa1498dc4f2, usgsgroundwatermodel
Organization: Department of the Interior