Comparison of measured and predicted nearshore sediment grain-size distribution patterns,southwestern Lake Michigan,U.S.A.

Comparison of calculated grain sizes with those found in a part of the shoaling zone of south western Lake Michigan reveals that existing quantitative expressions yield sizes which are much larger than those of the natural sediments, but that many aspects of the pattern of size distribution are predictable. An empirical and a theoretical expression were each used to calculate grain sizes in equilibrium with several different wave states for the measured bathymetry. For each wave state, the theoretical equation yields sizes which are closer to those found in the field over most of the shoaling zone, but sizes predicted by each of the two equations approach each other as the shore is approached and natural slopes increase toward the slope used in formulating the empirical expression. Grain-size trends predicted by the calculations include coarsening toward shore and to the south near shore. The calculations with the theoretical expression reveal more detail and predict an anomalously coarse area in the deeper part of the field area and elongate areas of fine sediments close to shore. Some support for the existence of these areas was found in the field.