Projects Hydrologic Monitoring and Watershed Modeling Associated with the Great Marsh Restoration Project, Indiana Dunes National Lakeshore Overview by Denver Harper, Greg Olyphant, and Alex Zlotin

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PROJECT SUMMARY

In cooperation with the National Park Service (Indiana Dunes National Lakeshore, IDNL) and Purdue University (North Central), the Department of Geological Sciences of Indiana University (IU) and the Indiana Geological Survey (IGS) initiated a project to monitor outfalls of bacterially contaminated water from the Derby Ditch Watershed, which drains a degraded portion of the Great Marsh. The project was also designed to evaluate the effects that restoration of parts of the Great Marsh might have on the marsh's hydrology and on the mitigation of bacterial contamination. The project was sponsored by the Indiana Department of Environmental Management (IDEM), the National Oceanic and Atmospheric Administration (NOAA), and the Great Lakes Commission (GLC). The term of the study was from January 1997, through June 2000.

PROJECT SCOPE AND CHRONOLOGY

Aerial photograph showing the plume of Derby Ditch discharging into Lake Michigan.

This project was developed from recommendations made by the Interagency Task Force on Escherichia coli, whose members, in the summer of 1996, drafted an umbrella Work Plan for addressing the problem of beach closures. The recurrent closure of bathing beaches due to excessive levels of fecal bacteria (E. coli) and other contaminants, which represent a threat to human health, has negative impacts on the entire economy of northwestern Indiana, and data indicate that the problem may be getting worse. A key element of the Work Plan was the initiation of an electronic monitoring network at the outlets of the main streams that discharge contaminated water into Lake Michigan. The Work Plan also included recommendations for remediation measures in areas that were suspected to be sources of bacterial contamination.

Derby Ditch flowing into Lake Michigan.

Derby Ditch was selected for the pilot investigation because it is one of the most bacterially contaminated streams discharging into Lake Michigan from northwest Indiana. Derby Ditch is an artificial drainage that was constructed to drain part of the once extensive Great Marsh. The modeling and monitoring of wetland hydrology for restoration purposes was considered important because one working hypothesis of the Task Force is that wetlands serve to treat contaminated streamflow through natural biodegradation.

The components of the project included the following: (1) development of an interactive model for previewing wetland restoration through ditch plugging; (2) intensive monitoring of hydrologic conditions in a portion of the Derby Ditch watershed within IDNL that was scheduled for restoration by personnel of the IDNL; (3) monitoring of E. coli concentrations in streamflow discharging from the Derby Ditch watershed into Lake Michigan; and (4) development of a statistical model for forecasting outfalls from Derby Ditch, which would could be used as part of an Early Warning System for Beach Closures.

Weather station used during the project.

The data collection phase of the project commenced in May 1997. Electronic monitoring included stream-discharge and water-quality parameters (specific conductance, temperature, and turbidity) at the outlet of Derby Ditch and at another site located approximately 720 m upstream of the outlet. Electronic flow meters were also installed in a tributary of Derby Ditch near the IDNL Campground and in another unditched tributary near the IDNL Visitor's Station. A weather station for measuring rainfall and other data pertinent to calculating potential evapotranspiration was established in a drained part of the Great Marsh near Derby Ditch. Instruments for monitoring water-table fluctuations and soil temperatures were also installed at that site. Installations for water-table monitoring were also placed near the Beverly Shores Town Hall and in a portion of drained wetland, up-drainage from the IDNL Campground. Data on E. coli concentrations in streamflow were collected and analyzed by personnel of Purdue University (North Central) throughout the spring and summer of 1997.

Monitoring station above the outlet of Derby Ditch.

Prior to the beginning of this study, a water-control structure existed in the ditch that drained the wetland area around the site near the town hall, but personnel of IDNL removed it in 1998, in preparation for their more aggressive program of ditch pluggings and drainage diversions. They had originally planned to commence their marsh-restoration efforts as early as autumn 1997. However, restoration never really began until autumn 1998. By spring 1999, ditch plugging and drainage rearrangements had been completed near the town-hall ground-water monitoring site, and the main ditches immediately upstream from the IDNL Campground had been plugged using checkdams.

Additional E. coli monitoring was conducted during the summers of 1999 and 2000. These samples were analyzed in the laboratories of the Lake Michigan Ecological Research Station (LMERS) in Porter, Indiana, under the supervision of Angel Gochee of the Department of Biology, Indiana University (Northwest).

Throughout the duration of the project, dry summer weather hindered collection of data during storms. Data were collected from a total of nine separate storms, but complete datasets were obtained only for the outlet of Derby Ditch. Also, the monitoring stations at the study site were vandalized on numerous occasions during the duration of the project. Monitoring continued through spring 1999, but at a reduced scale due to the shortage of equipment.

Example graph showing the relationship between discharge and the concentration of E. coli during a storm in June, 1997.

SIGNIFICANT FINDINGS

E. COLI IN STREAMFLOW

Samples of streamflow using autosamplers yield values of E. coli concentrations that are equivalent to samples collected using the traditional grab method.

There is a slight, but not dominant, tendency for E. coli concentrations to be greatest during the rising phase of a storm hydrograph and for the concentrations to decline as the hydrograph recedes.

Turbidity tends to rise and fall during the initial phases of a storm hydrograph in a manner similar to that of E. coli concentrations. However, this trend is not universal and may only occur in response to intense isolated rainfalls that serve to flush bacteria from source areas within the watershed.

A statistical regression equation for estimating outfalls of E. coli to Lake Michigan from the Derby Ditch watershed accounts for approximately 75 percent of the observed variability of outfalls during the 1997 and 1998 swimming season. Equations of this type may form the basis of an Early Warning System for beach closures.

An example of output from the model for predicting the effects of ditch closures.

WETLAND-RESTORATION HYDROLOGY

A user-friendly, GIS-based model for previewing the likely effects of ditch closures has been developed, and supporting data (including requisite GIS layers) have been compiled for application to the Derby Ditch watershed.

Wetland restoration efforts in the Great Marsh have resulted in saturation conditions in the cool seasons of late autumn, winter, and early spring, but water levels are still dropping as much as one meter below the ground surface during late summer and early autumn.

Ditch closures above a tributary of Derby Ditch, near the campground of the Indiana Dunes National Lakeshore, have resulted in a significant reduction of storm discharge. E. coli concentrations in stream flow remain high, but total outfalls have declined due to reductions of storm discharge.

For a detailed technical report on the investigation, go to the Great Marsh Restoration Web page. NOTE: Because it contains a number of graphics with large file sizes, the technical report is best viewed with a high-speed internet connection.

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For additional information, contact Greg Olyphant (e-mail: olyphant@indiana.edu) at the Department of Geological Sciences, Indiana University, Bloomington, IN 47405, or Denver Harper (e-mail: dharper@indiana.edu) at the Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47405