- Abstract: Please see metadata under each individual feature layer and table for more information.
In order to support science-based water resource management, a systematic effort was undertaken to characterize the nature and function of the hydrogeology in Jo Daviess County, Illinois. Jo Daviess County is a karst area. Karst is a geologically and hydrologically integrated or interconnected and self-organizing network of landforms and subsurface large-scale, secondary porosity created by a combination of fractured carbonate bedrock, the movement of water into and through the rock body as part of the hydrologic cycle, and physical and chemical weathering (Panno, S.V. et al, 2017). Springs, cover-collapse sinkholes, crevices, and caves are among the defining features of a karst terrain; each of these features is found in Jo Daviess County. Examples of these features have been located in the field and characterized by scientists from the Illinois State Geological and Water Surveys (Prairie Research Institute, University of Illinois at Urbana-Champaign).
An unforeseen outcome of the 2012 summer drought that impacted the U.S. Midwest and adversely affected the health and vigor of agricultural crops was it provided a rare opportunity to examine the fractured, creviced, and buried bedrock surface of northwestern Illinois. Complex vegetated networks, referred to as ‘crop lines’, began to appear across the dry summer landscape of Jo Daviess County, Illinois, including adjacent western Stephenson County and southwestern Wisconsin. Primarily confined to alfalfa hay fields, the vegetated crop lines resulted from a combination of three factors: 1) the persistent extremely dry conditions, 2) a relatively thin (3 to 5 feet) overburden of unconsolidated deposits, and 3) a highly fractured and creviced bedrock surface comprised of Ordovician age Galena Dolomite.
Alfalfa’s vigorous root system, which may ultimately extend to depths of 6.1 m (20 feet) or more, enables it to obtain water and nutrients moving through bedrock crevices near the top of the karst aquifer, providing the necessary moisture during the 2012 summer drought to sustain the overlying healthy alfalfa plants, whereas the remaining field area exhibited stunted and sparse plant growth. The alfalfa plants forming the crop lines tended to grow denser, taller (0.5 m vs. 0.15 m), and greener than those in adjacent areas, were clearly visible from vertical aerial photographs, and provided a visual representation of the bedrock fracture pattern below. Work on this project was funded by the Illinois State Geological Survey.
The publication cited below provides background and context:
Panno, S.V., Donald E. Luman, and Dennis R. Kolata. Characterization of karst terrain and regional tectonics using remotely sensed data in Jo Daviess County, Illinois, Circular 589, Illinois State Geological Survey, Prairie Research Institute, University of Illinois Urbana-Champaign, 2015. https://www.isgs.illinois.edu/maps/county-maps/karst-terrain/jo-daviess
Panno, S.V. and D.E. Luman. Assessment of the geology and hydrogeology of two sites for a proposed large dairy facility in Jo Daviess County near Nora, IL. Illinois State Geological Survey Open File Series 2008-2, 2008. https://library.isgs.illinois.edu/Pubs/pdfs/ofs/2008/ofs2008-02.pdf
Panno, S.V., Philip G. Millhouse, Randy W. Nyboer, Daryl Watson, Walton R. Kelly, Lisa M. Anderson, Curtis C. Albert, and Donald E. Luman. Guide to the Geology, Hydrogeology, History, Archaeology, and Biotic Ecology of the Driftless area of Northwestern Illinois, Jo Daviess County. Illinois State Geological Survey Guidebook 42, 2016. https://www.isgs.illinois.edu/publications/gb042
Panno, S.V., Donald E. Luman, Walton R. Kelly, Timothy H. Larson, and Stephen J. Taylor. Karst of the Driftless Area of Jo Daviess County, Illinois. Circular 586, Illinois State Geological Survey, Prairie Research Institute, University of Illinois Urbana-Champaign,2017. https://isgs.illinois.edu/maps/county-maps/karst-terrain/jo-daviess
- Purpose: This dataset contains digitized bedrock crevice locations, a direct indicator of karst terrain, for Jo Daviess County, IL. The primary source data used for the digitizing was multitemporal aerial photography acquired from multiple sources during the period of June-October, 2012. This is one of several datasets compiled for the Karst Feature Database of Jo Daviess County, IL and hosted by the U.S. Fish & Wildlife Service. Thumbnail photo credit: Illinois State geological Survey and Illinois Department of Transportation, Aerial Survey Division.
- Supplemental Information: Croplines can reveal crevice and fracture patterns present in bedrock. These lines are only visible during drought conditions and only in areas with very shallow soils where alfalfa is grown. Non-detection of croplines does not imply the lack of fractures and crevices in bedrock.