Challenge
Much of the Lake Michigan shoreline in Wisconsin has a coastal bluff varying in height from less than 20 feet to over 140 feet. These bluffs erode in a number of ways and at varying rates (Figure 1). Over 175 profiles of these bluffs were measured and analyzed for slope stability in the mid-1970s and again in the mid-1990s. These profiles were measured with a hand held inclinometer and tape and are stored as XY plots on paper. These profiles were also located as accurately as possible on aerial photos, but they were not located in a GIS. Our challenge was to re-measure these bluff profiles in a relatively short time and on a small budget so that we could document the changes that have taken place on the bluffs during the last 40 years and to use this input as a basis to determine bluff stability over time.
Solution
To achieve this goal we obtained and processed 2012 USACE LIDAR data for much of Wisconsin’s Lake Michigan shore. Using LP360 for ArcGIS (QCoherent Software, LLC) we re-projected to a Wisconsin coordinate system and performed verification of LIDAR classification quality (e.g. bare earth, trees, buildings). LP360 also allowed for rapid drawing of profiles from bluff top to lake edge. Correctly classified LIDAR points easily allow the separation of bare earth and other features such as trees and buildings. Figure 2a shows a profile with vegetation included and Figure 2b shows the ground surface with vegetation filtered out and a line draped to the surface to make it more easily visible.
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