A reduced-complexity shoreline model for coastal areas with large water level fluctuations

Abstract

A new reduced-complexity, 1-D shoreline model has been developed, calibrated, and tested with a set of shoreline positions detected from high-resolution satellite images. Motivated by recent large interannual water level fluctuations and associated shoreline changes in the Great Lakes, the model is built on previous models that are based on the disequilibrium concept, with extensions for water level effects. Unlike other shoreline models, the model includes two different sources of disequilibrium, wave disequilibrium and water level disequilibrium. The model also includes a passive flooding term to account for the instantaneous effect of the water level changes on the shoreline position. Case studies forced by seasonally-varying waves and water levels varying on seasonal and interannual timescales highlight the model's ability to enhance wave-driven shoreline change when water level variations are additionally present. The model was applied to two sites along the Lake Michigan shoreline, Jeorse Park and West Beaches, with shoreline time series extracted from multispectral satellite imagery. When calibrated and applied to an eleven year period of decreasing water levels, the new model shows significant skill in simulating and forecasting the shoreline position in the two study areas, with modest improvement over existing models. The simulation results additionally highlight the dominance of water level disequilibrium over wave disequilibrium for the study sites. When applied to a nearly forty year simulation of West Beach, the new model shows excellent ability to model the shoreline response to water level and wave fluctuations over a range of timescales. Comparison models are seen to be incapable of capturing the water level effects, particularly when water level trends differ from the calibration period. Overall, the model results and parameters show the importance of the newly introduced water level disequilibrium in modulating wave-driven shoreline change. Finally, while the shoreline model was motivated by Great Lakes coastal processes, it may provide new predication abilities for coastlines where water level fluctuations and trends play a role in shoreline changes. • A new shoreline model is developed, tested, and compared to existing models. • The model is based on the concept of combined wave and water level disequilibrium. • The model is applied to two case studies along the Lake Michigan shoreline. • The model successfully simulates shoreline changes enhanced by water level changes.