PHOTOGRAPHY AS A TOOL IN DOCUMENTING BEACH EROSION AND MIGRATION OF LARGE COASTAL DUNE ALONG SOUTH SHORE OF LAKE MICHIGAN

We present here a series of photographs which show significant changes in coastal morphology along south Lake Michigan that occurred in last seventy years. Development in Michigan City and erection of piers, groins, and sea walls significantly changed longshore current behavior. Rapid accumulation of sand in Michigan City Harbor (up current from anthropogenic structures) requires frequent dredging, while severe beach erosion occurs immediately down current from the structures. Even though more than 1 million tons of sand has been nourished near the Mt. Baldy beach since the early 1970’s, beach erosion and migration of the large dune still continue. A series of aerial photographs depict changes in the beach position and dune morphology that happened between 1938 and 2008. We measured 145 m of beach erosion (2.1 m/year) over this period, but erosion rates were much higher (7.8 m/year) during the highest Lake Michigan levels (1983-87). The beach prograding of 2 m/year (1987-90) and 13 m/year (1995-99) reflects extensive beach nourishment (68,000 t, and 273,000 t, respectively) that only temporarily halted beach erosion. Aerial photographs reveal that Mt. Baldy dune changed from a long (1470 m) and narrow (280 m) transverse dune to a shorter (680 m) but wider (360 m) parabolic type of dune and migrated 246 m (3.5 m/year) inland. In May 2007 we began monitoring sand accretion rates and inland migration of the Mt. Baldy slipface. After two years of observation we report that maximum sand accretion (6 m) and slipface advance (9.1 m) occurred along the parabola axis. A series of field photographs taken at four to six week intervals illustrate the position of the slipface at measuring stations. We will also present seasonal changes in the morphology of the dune brink and its upper slipface, as well as unusual modes of wet sand transport at this dune.