BLUFF PROFILE CHANGES OVER 40 YEARS ON WISCONSIN'S LAKE MICHIGAN SHORELINE
Because the locations of these older profiles were marked on air photos, and not located using GPS, their locations cannot be verified to be exactly correct. Also, because there is no spatial control on the top or base of previous profiles, this comparison cannot be used to measure bluff top recession rates. It is possible, however, to 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 was there in the mid-1970s or mid-1990s. Of the 190 1976 profiles that were “re-occupied” in 2012, 161 increased their factor of safety, 3 had safety factors that remained the same, and only 26 showed a decrease in factor of safety between 1976 and 2012.
Presumably this is mostly because of generally low lake levels over the past few decades. Data from our studies of erosion of Wisconsin’s Lake Michigan and Lake Superior shorelines since the 1970s, have been recently posted at: http://floodatlas.org/wcmp/obliqueviewer/. These include low-level oblique photos from the 1970s, 2007, 2008, 2012, 2016 and 2017, mapped evaluation of bluff conditions along the shore from 1970s and 2007-2008 based on interpretation from oblique air photos, shore structures in 1976 and 2007 and 2008, and bluff and bathymetric profiles from 2012. See also: http://floodatlas.org/wcmp/obliqueviewer/about.html