CONTEMPORARY AND HISTORICAL RATES OF EOLIAN SAND TRANSPORT IN THE INDIANA DUNES AREA OF SOUTHERN LAKE-MICHIGAN

As part of an effort to elucidate the role of eolian processes in the sediment budget of southern Lake Michigan, an 8-yr record of wind data was used to drive a model for simulating eolian sand transport along the southern shoreline. Computer simulations indicated that the potential rate of sand loss from the shore zone is currently between 1.2x10(3) and 2.7x10(3) kg per meter of shoreline per year. The sand, which is transported by strong northerly winds across vegetated foredunes and blowout dunes, is deposited in the backdune areas where it cannot be recycled by storm waves. The contemporary (short-term) rate of net sediment loss from the shore zone (ca. 2x10(3) kg m-1 yr-1 on the basis of the computer simulations) is 40 percent greater than an estimate based on dated eolian accumulates in relict beach ridges (1.4x10(3) kg m-1 yr-1) but an order of magnitude less than the average rate of accretion during the last 3,000 years (ca. 1.7x10(4) kg m-1 yr-1). Throughout most of the late-Holocene littoral drift from the northeast and northwest was sufficient to ensure beach growth despite the removal of sand by northerly winds. However, the construction of numerous breakwaters updrift of the Indiana Dunes area has disrupted the natural sediment balance so that eolian transport is contributing to beach erosion. The potential loss of sand from the backshore by net eolian transport is equivalent to about 150 mm of shoreline retreat per year.