VIDEO MONITORING OF NEARSHORE ICE IN SOUTHERN LAKE-MICHIGAN

We set up a time-lapse video camera system on the southwestern shore o f Lake Michigan for 16 days in January and February 1991 to monitor ic e conditions. The system was used to determine longshore and cross-sho re ice-drift rates in a zone of mobile brash and slush ice on 11 days. Daily mean longshore ice drift was to the southeast on 10 of these da ys at speeds ranging between 0.047 and 0.377 m s-1. Mean cross-shore i ce drift was always offshore and varied between 0.009 and 0.126 m s-1. Shear and strain were rare in the brash/slush zone. On 6 of the days when drift rates were determined, we were also able to determine the w idth of the brash/slush zone. Using these data along with published va lues of ice thickness, ice concentration, and sediment concentration i n ice, we were able to estimate longshore and cross-shore sand fluxes and longshore sand transport rates. The longshore and cross-shore ice- induced sand fluxes ranged from 0.008 to 0.760 t hr-1 and 0.0016 to 0. 096 t hr-1, respectively. Net ice-induced longshore sand transport was to the south at rates of 1.8 to 83.7 t hr-1. Measured cross-shore san d flux was consistently offshore. The calculated fluxes indicate that large amounts of sand are moved alongshore and offshore by ice in sout hernwestern Lake Michigan during the winter months.