The 1998 Coastal Turbidity Plume in Lake Michigan

Abstract

In this paper, numerical models of coastal circulation, wind-waves, and sediment transport are applied to the March 1998 turbidity plume event in Lake Michigan to investigate the role of wind-induced circulation in the offshore transport of sedimentary material in Lake Michigan. Computer visualization is used to compare model results to the evidence of cross-isobath transport suggested in satellite imagery. Model results showed that circulation in Lake Michigan is highly episodic since it is almost entirely wind-driven in early spring. The characteristic wind-driven circulation pattern in the lake consists of two counter-rotating gyres, a counterclockwise-rotating gyre to the right of the wind, and a clockwise-rotating gyre to the left. The gyres are separated by a convergence zone along the downwind shore with resulting offshore flow and a divergence zone along the upwind shore with onshore flow. This two-gyre circulation pattern with offshore flow was very clearly seen during a northerly wind event in March 1998 in southern Lake Michigan. The strongest sediment resuspension occurred in the southern lake and the shallow waters along the coastline. This is because of the larger waves in southern Lake Michigan due to the dominant northerly wind in this early spring period. The two most significant sediment resuspension events were detected in the model results during the two storm events. Although results from the sediment transport model agree qualitatively with satellite imagery, they fail to simulate the initial eddy-like structure of the plume. Visualization is shown to be an effective tool for interpreting the complex turbidity patterns in the satellite imagery of the turbidity plume.