THE INFLUENCE OF MICROCLIMATE ON SAND MOVEMENT BY WIND AT AN EASTERN LAKE MICHIGAN COASTAL DUNE SITE

Along the eastern shore of Lake Michigan, sand transport by wind creates foredunes and modifies the existing dune ridges and parabolic dunes. Ongoing research in P.J. Hoffmaster State Park (Muskegon, MI) is monitoring the rates and patterns of sand movement and dune change in a beach-dune system that includes a foredune, dune ridge, and incipient blowout. The present study investigates the influence of local climate variables on the movement of sand by wind within the beach-dune system.

Geomorphologic and microclimate data were collected at the Lake Michigan study site from October 2001 through April 2002. Sand movement and dune change were monitored by means of Leatherman-style sand traps and an array of erosion pins. The sand traps were placed in rows at the beach-foredune boundary, on the crest of the foredune, at the foredune-dune ridge boundary and at the crest of the dune ridge. Microclimate data recorded at the site include wind speed at 5 heights, wind direction, air and soil temperature, and relative humidity. Data on snow cover and surface moisture content were obtained during regular site visits.

Local wind patterns control the amount, timing and direction of sediment transport in the beach-dune system. Temperature and precipitation influence ground-freezing and snow-cover of beach and dune surfaces, thereby decreasing sediment supply to aeolian processes or immobilizing the sediments altogether. In the dynamic coastal environment, such immobilization is temporary. Spatial patterns of transport and deposition are linked to the topography and vegetation of the site. The well-vegetated foredune ridge has reached a sufficient size to capture most of the sand moving east from the beach. The dune ridge, located landward (east) of the foredune, receives no new sediments from the beach but experiences local movement of sand from the blowout to the dune crest and lee-slope. Topographic influences on snow accumulation and surface moisture content also affect sediment transport patterns.

Despite restrictions imposed by ground-freezing, snow-cover, surface moisture, and topographic protection, the winds along the east Lake Michigan shoreline are able to move significant amounts of sand inland during the late fall, winter, and early spring.