NUMERICAL MODELLING OF LAKE MICHIGAN SHORELINE EROSION: POINT BEACH STATE FOREST, WISCONSIN

Lake Michigan experiences quasi-decadal fluctuations in water levels that impact navigation, tourism, shoreline position and coastal habitat. Recent above average lake levels are a concern for homeowners and policy-makers due to significant shoreline recession. Nearshore waves, currents and bathymetry are major factors influencing local sediment transport and shoreline behavior, but rigorous numerical models of these processes are largely absent in the Great Lakes and frequent “real-time” surveying of coastal change can be cost prohibitive for small communities. As such, there have been few attempts to quantitatively estimate potential rates and extents of wave-driven erosion and nearshore sediment transport at sandy coastal systems in the Great Lakes, particularly in response to fluctuations in lake level. In this study we numerically model nearshore sediment transport and resulting changes in sandy beach and nearshore morphology to estimate future coastal geomorphic change in response to storms and varying lake levels.

Bathymetric surveying was conducted on the western shoreline of Lake Michigan near Point Beach State Forest. The survey extended lakeward from the active shoreface to the approximate depth of closure (20 m isobath). High-resolution topographic surveying of the beach was collected concurrently with the bathymetric surveys, as well as immediately before and after the first high-magnitude storm. Timeseries wave data from the Great Lakes Coastal Forecasting System nowcast simulations were used as input for beach morphological model XBeach. Hindcast simulations were used in preliminary calibration of the model and accuracy assessment of predicted subaerial shoreface changes. Additional model validation will be performed pending repeat bathymetric surveys and acquisition of in situ wave data using pressure transducers. Following satisfactory hindcast simulation of morphologic evolution, input data will be modified to simulate the response of the nearshore environment to cyclical fluctuations in Lake Michigan water levels.