Seasonal Variation of a Limnic Beach

Abstract

A seasonal beach process-response model has been constructed for limnic beach environments. Unlike marine environments where seasonal changes in beach configuration are determined by seasonal variations of wave regimes, limnic beaches respond to seasonal variations in lake water levels. Along the beach of Lake Michigan at Terry Andrae State Park, Wisconsin, field evidence has shown that with rising lake level from April through July, the foreshore migrates inland on an upward inclined plane, decreasing both beach and back-shore width, and decreasing the elevational difference between an overhead fixed plane and the foreshore crest and beach step. These processes are reversed when lake level subsides from August through November. The net result is that the beaches of Lake Michigan, and presumably those of the remaining Great Lakes, retrograde from spring to summer, and prograde from summer to winter. Not all beach characteristics vary with seasonal fluctuation in lake level. In general, foreshore slope and width are independent of lake level. Foreshore slope is directly linked to the density of the foreshore sediments, while foreshore width is directly proportional to wave dimensions and is found to be independent of the foreshore slope.