Geologic and Hydrologic Report

A Geologic Information System and Hydrologic Survey of Wolf Road Prairie Nature Preserve Westchester, IL.

Prepared by: Ana Cichowski, Lacy Smith, and James Clark
Wheaton College, Wheaton, IL

June 2, 2004

Purpose of Project: The main objective of this project was to understand the hydrology of Wolf Road Prairie by gathering, organizing, and analyzing data into a Geographic Information System database. With this information a groundwater model for the site is being developed. The results of this analysis will aid in the preservation and management of the prairie.

GIS Mapping: Using Global Positioning System (GPS) technology a map of the current actual outline of the prairie and prairie features was drawn. The data was collected by slowly walking the GPS unit along the sidewalks, paths, monitoring wells, and trenches of the prairie while the unit took readings from satellites. The readings were corrected for errors by using the information from a local fixed GPS base station.

GIS Analysis: The GIS map database is helpful in recording, compiling and maintaining prairie data. It is also useful in providing a database of visual images, namely aerial photos.

The completed GIS database reveals interesting changes over time. The DOQ and 1938 aerial photograph show the sharp contrast between current and historical prairie development. The historical photo emphasizes the abundant farmland surrounding the prairie, with only Wolf Road and 31st street as obvious features. Photographed about 60 years later, the DOQ emphasizes the urbanization that now approaches the prairie borders. A significant increase in pavement and a noticeable rise of urbanization often trigger changes within places like Wolf Road Prairie because of the diversion of groundwater flow and the increase of surface runoff.

Hydrological Analysis: The ultimate goal of this survey is an analysis of the groundwater flow.

The intention is that these results can aid in understanding the migrating wetlands and changing prairie. A varying water table means the difference between a prairie, where plants must absorb air through their roots, and a wetland, where plants thrive in the saturated ground.

Seismic Refraction Survey: Seismic refraction is a geophysical method frequently used to determine depth to the water table, to geologic layers, and to bedrock.

Seismic refraction is a geophysical technique that uses the movement of seismic or sound waves to delineate geologic layers based on changes in seismic velocity of different strata. Analysis of this data provides an understanding of the subsurface nature of the prairie in relation to groundwater movement and drainage.

Seismic Refraction Results: The seismic results confirm that a distinction between soil types occurs at about 7 to 8 feet below the surface.

The velocity of the upper layer is consistent with a sandy/silty unconsolidated soil. The lower level velocity indicates a consolidated gravel/till horizon. Therefore, because of the impermeable nature of the lower horizon, the majority of the ground water affecting the prairie will be confined to the upper 7 to 8 feet.

Conclusions and Recommendations

This survey consisted of two parts: compiling and analyzing existing spatial data using ArcViewGIS and studying the hydrology of Wolf Road Prairie. The projects were interrelated in that GIS is helpful in understanding the layout of the prairie and the relationship it has with the hydrology. Both projects were largely successful, although more data would improve all of the results.

The GIS map database consists of: USGS topographic map, color air photograph, historical air photograph, digital elevation map (DEM), Global Positioning System (GPS) survey, ground penetrating radar (GPR) survey, and digital orthophotoquad (DOQ). If more data are collected, such as vegetation maps, bird/animal migration, wetland delineations, etc., they can be included in the GIS if accurate locations are available. The entire GIS can be imported into ArcExplorer, a free GIS reader. This freeware offers viewing, printing, and some analysis of the data.

The GPS information provided maps of the exact current outline of the prairie and prairie features. It would be of further benefit to the prairie to purchase a GPS unit for marking delineation of burn areas, wetland, prairie, and savanna areas, and vegetation distribution.

The hydrologic data and model simulations suggest that urbanization has had a large impact on the groundwater flow and seasonal groundwater levels. Thus the migration and shrinking of the wetlands may be directly related to the increased pavement and diversion of water from the prairie area, especially within the last 60 years.