LOCAL WIND, DEPOSITION AND EROSION PATTERNS DURING STORMS IN A TROUGH BLOWOUT AT SAUGATUCK NATURAL AREA, THE SOUTHEASTERN SHORE OF LAKE MICHIGAN

The directions of strong winds in Lake Michigan dunes often depend on the paths of extratropical cyclones and frequently rotate during the storm. Topographic steering further modifies directions of local winds responsible for sand transport. We observed wind and sand transport patterns in a trough blowout dune near Saugatuck on the SE coast of Lake Michigan during autumn and spring storms in 2011-2012 and 2015-2016 with an array of 6 to 9 anemometers and over 200 erosion/deposition pins. The main trough (MT) of the blowout opens to the NW and trends 325^o. The eastern limb of the trough is markedly higher than the western. A secondary trough (ST) on the western limb opens into the MT and trends 310^o. The dune has a steep south facing outer slope (SOS). Winds at the southern crest (SC) of the dune were typically the strongest measured and were usually roughly aligned with winds at the airport 7 km to the NE. Winds on the SOS and the SC were aligned when winds were E, SE, S, SW. When winds at the SC were W, NW, N winds on the SOS were usually NE or SW parallel to the slope. Under all regional wind directions winds in the upper MT were N-NW parallel with the MT axis. Winds in the lower MT tended to be weak and variable with a tendency to align with winds at the SC, sometimes creating bifurcated flow in the MT. Winds in the middle MT tended to be N-NW except when SC winds were W, in which case they were W blowing towards the eastern wall. Winds in the ST tended to align with the ST axis blowing out of the MT when SC winds were E,SE, S and blowing into the MT when SC winds were W,NW. Winds blowing into the MT from the ST are relatively strong approaching the strength of winds at the SC. A region of deflation aligned along the ST axis extends into the MT. The steep eastern wall was also a region of erosion. The central portion of the main trough was a region of deposition. If these patterns continue the axis of the blowout will rotate roughly 15^o towards the west.