BLUFF AND NEARSHORE PROFILES ALONG THE LAKE MICHIGAN SHORELINE NORTH OF PORT WASHINGTON, WISCONSIN

We have processed 2012 USACE Lidar data for all of Wisconsin’s Lake Michigan shore. We used LP360 (QCoherent Software, LLC) for ESRI ArcGIS software. LP360 allows drawing profiles from bluff top to water depths of at least 6 m in many places. In a previous study, 175 bluff profiles were constructed from the 2012 Lidar between Port Washington and the Illinois State line. Of these, 154 profiles were in the same location as a profile that was measured in 1976, 1995, or in most cases, both. This year, 132 profiles between Port Washington and Door County were measured. They include profiles that extend along the bottom in the nearshore zone out to a critical depth of about 6 m. Unfortunately, because the locations of the older profiles were marked on air photos, and not located with GPS, their locations cannot be verified to be exactly correct and therefore this profiling cannot easily be used to calculate the rate of bluff top retreat. 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. This appears to be the case in at least 80% of the profiles and is primarily due to relatively low lake level during the last decade and continued construction of revetments.