THE USE OF LIDAR IMAGERY AND AERIAL PHOTOGRAPHY TO CHARACTERIZE THE KARST AQUIFERS OF THE UNGLACIATED REGION OF NORTHWESTERN IL

A reexamination of the karst features commonly observed in the carbonate bedrock of Illinois’ driftless area, northwestern IL, was prompted by an application to the Illinois Department of Agriculture to build two industrial-scale dairies in eastern part of the county. In so doing, we examined aerial photographs and recently-available LiDAR imagery, in conjunction with field investigations that included all of Jo Daviess County.

LiDAR imagery revealed abundant lineaments throughout the county. Work by Richard Parizek and others has shown that lineaments in areas of carbonate bedrock have a 75% chance of being principal groundwater pathways. Lineament orientations coincided with those of crevices found in road cuts and quarries in the county, and published crevice orientations by the ISGS and USGS for that area. Lineaments seen on LiDAR imagery were coincident with those seen on aerial photographs. Every road cut and quarry visited in the county contained abundant solution-enlarged crevices whose spacing ranged from several meters to 10 meters. The width of these crevices in Jo Daviess Count ranged from a centimeter to greater than a meter; the widest of the crevices trend in a nearly E-W direction. In addition, cover-collapse sinkholes (1.5 to 8 m in diameter), large springs (typically round, circular depressions), and long, narrow indentations in the banks of stream channels in the area were coincident with and oriented in the same directions as lineaments that intersected the proposed sites. Whereas no sinkholes were identified on the proposed dairy sites, an 8 m diameter sinkhole located less than 600 meters from the southern edge of the south dairy site was found along a prominent lineament (N 20^o W) that intersected the site. The size of the sinkhole, based on those of Illinois’ sinkhole plain, suggests that the underlying crevice is at least 0.2 to 0.5 meters wide. An even more prominent lineament,14 miles in length and oriented N 70^o W, is associated with Silurian-age dolomite knobs that are characteristic of the county and intersects the origin of Apple River Canyon. All of the lineament and crevice orientations in Jo Daviess County are similar to those of the major structures of the Illinois Basin (La Salle Anticlinorium (N 20^o W), Sandwich Fault Zone (N 60^o W), Plumb River Fault Zone (nearly E-W) suggesting a common origin.