ABSTRACT

A 4-year set of beach and offshore profiles, measured at monthly intervals, is evaluated to determine the effect of wind-wave forcing and long-term lake-level variation on profile change in the Great Lakes. This evaluation indicates three distinct areas of profile change: the beach-and-berm, the inner-bar, and the outer-bar regions. The beach-and-berm region exhibits a classical transition from a narrow highly eroded (winter) profile to a broad fully deposited (summer) profile, during ice free months. The inner bar moves actively under the influence of wind-waves, but appears to lack a well-defined seasonal pattern. The outer bar advances onshore from early spring to early winter in response to lake-level modulation of incident wind-waves. Empirical eigenfunction analysis is applied t these data in order to statistically quantify the significance of these observed changes. This analysis provided confirmation of a hypothesized long-term (years) variation of the outer bar in direct response to lake-level variation.