CHANGES IN BLUFF STABILITY ALONG THE LAKE MICHIGAN SHORELINE IN SOUTHEASTERN WISCONSIN OVER A 40 YEAR PERIOD

We have processed 2012 USACE Lidar data for part of Wisconsin’s Lake Michigan shore. The data required re-projecting to a Wisconsin coordinate system along with verification of Lidar classification quality (e.g. bare earth, trees, buildings). We used LP360 (QCoherent Software, LLC) for ESRI ArcGIS software. LP360 allows drawing profiles from bluff top to lake edge fairly rapidly and accurately. A total of 175 profiles have been constructed from the 2012 Lidar. Of these, 154 profiles were in the same location as a profile that was measured in 1976, 1995, or in most cases, both. Unfortunately, because the locations of these older profiles were marked on air photos, and not located with GPS, their locations cannot be verified to be exactly correct. In order to compare slope stability in 1976, 1995, and 2012, we calculated the factors of safety of the slope using STABL software. Factors of safety 1.00 or over are considered relatively stable or stable with respect to deep-seated failures. The bluffs have definitely become more stable since 1976. In 1976, the mean lowest factor of safety of 113 profiles was 0.85. By 1995, the 148 profiles analyzed had a mean lowest factor of safety of 1.28. By 2012, this number had risen to an average of 1.47 for 154 profiles analyzed. In 1976, 82 of the 113 profiles analyzed, or 73%, had a lowest factor of safety less than 1.00. In 1995, 57 of the 148 profiles, or 38%, had a lowest factor of safety’s less than 1.00. In 2012, 21 of the 154 profiles, or only 14%, had a lowest factor of safety less than 1.00. Of the 1468profiles that were analyzed from 1995 and 2012, 102 increased their lowest factor of safety, thus becoming more stable. Of the 148 profiles, 41 became less stable. We conclude based on all of the profiles that slopes are more stable, have more gentle slopes, and have more sediment accumulated at the toe of the bluff than in the mid-1970s or mid-1990s.