EFFECT OF CLIMATE CHANGE ON COASTAL EROSION AND MASS WASTING ALONG WISCONSIN'S GREAT LAKES SHORELINE

The author has collaborated with Dr. David Mickelson for nearly 40 years on erosion and bluff instability problems and the engineering characterization of glacial deposits of Wisconsin. This abstract is based on a class project by the students who took the author’s course “Seepage and Slopes” in Spring 2011 on the effects of expected climate change on shoreline. Erosion and mass wasting along the shoreline due to changes in lake water level, storm frequency, wind, wave action, evaporation, precipitation, ground water level, stormwater, runoff, freeze-thaw cycles, and ice coverage were investigated as a function of climate change over the next fifty years. Different impacts and responses are expected along Lakes Michigan and Superior. Current climate change trends suggest lake levels lower in Michigan and higher in Superior. The bluff materials, although a product of glaciation, have markedly different engineering properties along each lake.

The predicted decrease in lake levels will tend to decrease wave erosion along the Lake Michigan shoreline; however, it may increase lakebed down-cutting and combined with the predicted increase in storms may result in enhanced shoreline erosion. The expected precipitation increases could cause more runoff and increased infiltration through bluffs leading to more surface erosion and increasing groundwater levels. The stability of natural slopes will be altered, and under certain conditions, currently stable soil slopes will become unstable and could lead to catastrophic deep-seated rotational failures.

Along Lake Superior shoreline, predicted increase in lake levels with increasing wave action and erosion. Precipitation around Lake Superior is projected to be less frequent, but more intense. Changes in soil properties due to wetter conditions and increased extreme weather will lead to an increase in shallow slips and debris flows. A rise in temperature that will increase the melting processes and decrease snow cover will increase the overall process of solifluction over the next century.

Since actual conditions are difficult to predict because of varying slope conditions along Wisconsin’s shoreline, continued monitoring of slope conditions is pivotal, and maintaining up-to-date analyses of stability is necessary as climate changes continue to occur.