Simulating Coastal Evolution Using a New Type of N-Line Model

This paper introduces an N-line model for predicting long- as well as short-term beach changes. Previous N-line models have not yet been very successful, mainly because they were not based on realistic relations for cross-shore sediment transport and for the cross-shore distribution of the longshore transport. The model is formulated as a classical N-line model using an arbitrary number of layers. The cross-shore sediment transport rate is calculated as a product of potential transport rate and the actual local bottom slope relative to the local equilibrium slope. This transport is divided between the layers based on a transport distribution across the surf zone. In the longshore direction the transport rate is based on the CERC equation, again with a division between layers according to an across-shore transport distribution function. A calibration/validation application of the model to a data set from the US Army Field Research Facility at Duck, North Carolina, showed that the model results agreed quite well with measured long-term field data. In addition, the applicability of the model to predict short-term beach evolution is demonstrated through an illustrative example.