Morphological modeling of a nourished bayside beach with a low tide terrace

摘要

We present a simple one-dimensional process-based morphological model for predicting medium-long term beach profile evolution of a bayside beach with a low tide terrace. Bayside beaches are characterized by low wave energy. In regions with a large tidal range, a beach face is slowly eroded due to erosional waves inside the surf zone which shifts along the beach profile over a wide range during a tidal cycle. The model is devel-oped using an existing model framework proposed by Mariotti and Fagherazzi (2010), who formulated a model for sediment suspension and transport due to waves and tidal currents in a tidal flat regime. The new developments in this study include an implementation of the bedload sediment transport and modifica-tion of the suspended load transport for noncohesive particles. The model parameters were calibrated using beach profile data collected over a one-year span at Xiamen Beach. Numerical experiments indicate that waves suspend sediment in the narrow surf zone, inducing pulse-like high sediment concentration in shallow water. The suspended sediment is adverted by the tidal current and wave-induced undertow, causing erosion of the steep beach face at the upper portion and deposition of the flat beach face at the lower portion of a beach profile. The erosion on the upper beach face was not predicted by a bedload-only transport model, suggesting that the sediment suspension associated wave breaking may be the major mechanism for the ero-sion. Tide-only induced sediment transport is insignificant, but tides play a role in distributing the wave-induced erosion over a wide region on a beach profile.