Utilizing Electrical Resistivity Imaging Techniques to Evaluate Karst Hazards in Agricultural Land Planning Decisions

In southeastern Minnesota, land use and planning issues must be considered in relation to the special challenges of living and building in karst terrain. These challenges include poor soils, considerable spatial variation in the depth to bedrock, potential for sinkhole development, and the protection of water resources. These issues have often made decisions to permit agricultural expansion controversial in our region. At least some of the controversy arises due to a lack of robust subsurface data upon which karst hazards can be identified and the associated risks evaluated. In partnership with the Winona County Planning Department, the Water Resources Center at Winona State has explored the use of Electrical Resistivity Imaging (ERI) to provide better data about the subsurface for planning decisions. The hope is that better data and higher certainty about the subsurface geology will reduce the contention that sometimes arises during the review of these permit applications. Initially, to build confidence in the usefulness of the technique we imaged areas where the subsurface features were known based on other evidence, including a known cave, or where excavations were about to occur. In addition to karst hazards, we have found the ERI data to be useful in predicting the depth to bedrock as well as the subsurface soil and rock stratigraphy and structure. Recently, ERI data was presented to the county Planning Commission as part of the permit review process. The presentation included an introduction to ERI techniques and applications to educate participants about the technique. Since many factors, both scientific and political, play into such decisions it is difficult to assess how much the ERI data contributed to a smooth hearing. However, we are optimistic that ERI data will play an increasingly important role in county planning decisions.