This study concerns erosion of the bluff or edge of the terrace marking the landward boundary of the beach at 17 sites along a 250-mile segment of the east coast of Lake Michigan. Data were collected every 4 weeks for 3 years beginning in August 1970, during a period when mean monthly lake levels in Lake Michigan rose about 1. 5 feet to record levels in the spring and summer of 1973.Bluff or terrace erosion was intermittent during the first 2 years, but universal during the final year, suggesting a critical lake level of about 580.0 feet, International Great Lakes datum (IGLD), above which erosion on this coast generally occurs everywhere. For the 3-year period, net bluff erosion varied from 1 cubic yard per foot of beach front at two sites, one in the north and one in the south of the study area, to a maximum loss of 39 cubic yards per foot at the site on Big Sable Point. Erosion within the study area was intermittent over time periods equal to the survey interval (4 weeks), and local compared to distances between sites (about 15 miles). Erosion increased with increase in lake level, although it is evident that lake level is merely a passive factor that permits waves to attack closer to the shore. Most erosion occurred during the late fall storm season when mean monthly lake levels were actually declining. Local factors, including bluff composition, shoreline orientation, occurrence of longshore bars, and protection from shore ice, appear to be important in determining erosion rates. Most of the sites in this study were away from the influence of coastal engineering structures. An aerial photo study of these sites from 1938 to 1972 showed that longterm erosion is closely tied to lake level. and that sand terraces form rapidly in the backshore during periods of low water. Beach sediments appear to be locally derived and sand size does not show a clear relationship to the slope of the beach face.
Coastal Changes, Eastern Lake Michigan, 1970-1973
Technical Paper ; TP 76-16
1976
4054933
Report
Elektronische Ressource
Englisch
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