An Evaluation of Two Cross-shore Numerical Models in Predicting Subaerial Beach Morphology

Abstract

Numerical modeling in the nearshore region has become an important tool in both planning and design for coastal engineers. In recent decades, the complexity of these models has increased as our knowledge of existing processes has matured. However, gaps still remain between what we as engineers understand about the nearshore environment and what actually exists. Due to these uncertainties, modelers have taken different approaches to simulate sediment transport.

The objective of this thesis is to evaluate the ability of two cross-shore numerical models, SBEACH and COSMOS, in their ability to predict subaerial beach profile change resulting from storm events. The predicted profiles from each model were compared to actual measured post-storm profiles. Quantitative comparison of results from both models was preformed using BMAP (Beach Morphology Analysis Package). A rating of good, fair, or poor was assigned to the models based on how closely each predicted the measured subaerial profile change. The waterline recession was also analyzed and a rating of reasonable or unreasonable was assigned to each model based on its predicted value.

The fundamental difference between the two models is in regards to sediment transport. The SBEACH model predicts sediment transport rates as a function of wave energy dissipation. The COSMOS model utilizes the energetics approach where sediment transport is dependent on mean velocity currents in both the bed and the suspended boundary layers. The results presented within this report show that SBEACH performed equally as well or better in each case. The COSMOS model consistently over predicted erosion on the beach face and recession of the waterline. For the study sites where data was collected for this research, SBEACH is the recommended model by the author.