| Studies documenting the roles that geologic materials and groundwater play in Great Lakes bluff recession are rare. This study reports findings concerning relationships between bluff lithology, bluff hydrology, and bluff recession along a 10-mile stretch of eastern Lake Michigan shoreline in heterogeneous Pleistocene deposits. According to a newly-developed, field-tested, GIS-based methodology, bluffs in the study area can be characterized lithologically as sand, clay, or mixed sand/clay, and can be characterized hydrologically as exhibiting either high head or low head.;Geotechnical analysis indicates that Atterberg limits, index properties, consolidation state, and drainage conditions affect the shear strength of bluff materials. Silty grey diamicton, a major constituent of clay-dominated bluffs, exhibits high undrained shear strength, and ;Results of Factor of Safety analyses performed upon bluffs at six field sites suggest that effective stress-based analyses that reflect long-term, drained conditions may be most appropriate in modeling recession in sandy bluffs of both high and low head, mixed sand/clay bluffs of both high and low head, and diamicton bluffs with high head. Diamicton bluffs with low head are apparently not destablilzed by groundwater; in this case, total stress-based Factor of Safety analysis may be an alternative method for modeling recession. |
