The objective of this task is to determine the interdependence between coastal processes and bluff stability. Many coastal processes may influence the stability of bluffs, such as the removal of beach surcharge at the toe of a bluff, notching at the toe of a bluff, and wave impact on the bluff face. Alternatively, bluff stability and ultimately failure can influence coastal processes by obstructing sand transport or protecting the erodible section of a lake bed.

Further analysis on these issues is taking place in 1999 to ensure the linkages between bluff stability and coastal processes are incorporated into the coastal process model being developed.

Some important work has recently taken place for the Allegan County shoreline by Dr. Bill Montgomery and in Wisconsin by Drs. Bosscher, Michaelson, and Edil. The geotechnical information being gathered at the site study areas should prove useful in further defining these interactions. This task will likely be highly qualitative drawing upon field observations, research and publications conducted by others outside the scope of this study. This will not be a lakewide function of the model and in most cases will require additional site specific data to apply this procedure. A secondary objective of this task will to assess the duration over which bluff stability is an important influence on recession rate calculations on a lakewide basis. Cross-shore and alongshore variability in stratigraphy will also be investigated.

The first activity consists of interpreting and extending the work completed by Dr. David Mickelson of the University of Wisconsin in Phase 2 to define uncertainty band widths based for all possible types of local bluff conditions found in each of the five prototype counties. As a first step in this activity, a review of the existing geomorphic shore classification was undertaken in order to ensure that it was sufficient (along with bluff height information) to capture shoreline types highly susceptible to deep seated failures.

The second activity consists of site-specific and short-term investigations of the links between coastal processes and bluff stability. In both Phases I and 2, the importance of completing this type of investigation has been acknowledged. It will provide for a better understanding of the short-term perspective of bluff evolution that relates to what riparians see versus the longer-term lakewide predictions that are required for the long-term potential damage assessments. These investigations are being completed at the Allegan County, Michigan study sites of Dr. Ron Chase from Western Michigan University (WMU). The WMU study sites exist within a 16 kilometer shoreline section where stratigraphy has been mapped every 60m. These sites were monitored on a bi-weekly basis for a period of at least two years. Assessments of groundwater conditions have also been completed at each of the sites and along a 24 kilometer reach of the shore. A detailed analysis of wave, erosion and runup conditions at each of the WMU study sites is being conducted using the Flood and Erosion Prediction System to develop a better understanding of the failure triggering mechanisms and to predict toe erosion for comparison to the WMU bi-weekly bluff evolution data set.

Baird is now in the process of developing a comparison of these findings with correlation between uncertainty band width and geomorphic type. The procedure developed under this task will then be applied in erosion damage assessments for the remainder of the Lake Michigan shoreline.

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