SAND ACCRETION RATES AND COASTAL DUNE INLAND ADVANCE ALONG SOUTHERN SHORE OF LAKE MICHIGAN

Mt. Baldy is a tall coastal dune located in IDNL, along the southeastern shore of Lake Michigan. Beach erosion caused by development in nearby Michigan City has induced the migration of Mt. Baldy dune inland. Sand accretion rates and dune inland advance are reported over a two year period (May 2007-09). Twenty six stations were set along the toe of the dune’s slipface. Vertical accretion of sand was recorded (during 4-6 weeks intervals), while slipface advance was calculated by the formula [h/tan(33^o·π/180^o)] and also measured in field. Climate data and Lake Michigan levels from the same observation period were analyzed. The maximum sand accretion (2.2 m/y in first season, and 3.8 m/year in second season), and slipface advance (3.4 m/year and 5.7 m/year, respectively), occurred in the central part of the dune. Higher rates of sand movement in second season coincided with ~ 20 cm higher Lake Michigan levels. The measured rates are several times greater than in similar dunes along the eastern Lake Michigan shoreline (Pettinga & van Dijk, 2008; Hansen et al., 2009). The highest accretion rates occurred during spring (March-May; 8.4 mm/day) and lowest during summer (June-August; 1.4 mm/day). Although the strongest winds occurred in winter (December-February) sand accretion rates were lower (4 mm/day) than in fall (5.7 mm/day). Frozen dune surface and snow limit sand transport in winter. Some sand transported over the dune brink remains temporarily stockpiled along the slipface and eventually descends to the toe as warmer spring weather removes moisture from the sand.