REVISITING 1970S AND 1990S BLUFF PROFILES ALONG THE LAKE MICHIGAN SHORELINE IN SOUTHEASTERN WISCONSIN USING USACE LIDAR DATA

We have obtained and processed 2012 USACE Lidar data for much 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 for ArcGIS software (QCoherent Software, LLC). This software allows drawing profiles from bluff top to lake edge fairly rapidly. Correctly classified Lidar points allow the separation of bare earth and other features such as trees and buildings. Output is a profile stored as a JPEG file (less useful) or XY values along the slope stored in an Excel spreadsheet (more useful). We have measured 184 bluff profiles between Kenosha and Port Washington, Wisconsin, and they are in the process of being analyzed for lowest factor of safety. We tried to measure profiles at locations of profiles measured between 1976 and 1978 and again in 1995. Because the locations of these older profiles were marked on air photos, and not using GPS, their locations cannot be verified to be exactly correct. Also, because there is no spatial control of previous profiles this comparison cannot be used to measure bluff top recession rates. Nor can the change in shape of any specific profile be documented confidently. 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. Presumably this is because of generally low lake levels over the past few decades. (Since the late 1990s the level of Lake Michigan has been at or below the long-term average of all of the time between 1970 and 2014.)