Narrow Results

Sediment transport caused by a tsunami was investigated by a simple experiment. We measured the horizontal velocities and suspended concentrations caused by one solitary wave, which is assumed to represent a tsunami passing on a planar sand bed without breaking or splitting. It was found that there are phase lags between peaks of suspended concentration and velocity, and the time variations of the vertical distribution of suspended sediment concentration are in good agreement with curve approximated with the exponential function. We found that Brown's formula is inconsistent with the time variations of sediment flux measured in the experiment because it cannot explain the phase lag between velocities or the total sediment flux. The bed load formula by Ashida-Michiue shows a close agreement with the amount of bed load.

A one-dimensional model for beach profile change was developed to predict longshore bar migrations. The cross-shore sediment transport was assumed to be composed of suspended load due to wave breaking and bed load due to velocity skewness, velocity atiltness, and beach slope. Beach profiles at the Hasaki coast in Japan during a 2-year period from 1989 to 1990 were predicted with a grid size of 5 m and time interval of 2 hours. The simulated profiles were compared with beach profile data, obtained along the 400-m-long pier of the Hazaki Oceanographical Research Station at 5-m intervals every workday and showing cyclic seaward bar migrations with a period of 1 year. The comparisons of the measured and predicted beach profiles and bar crest positions show that the model reasonably predicted the repeated seaward bar migration for about 2 years.

We present a three-dimensional sediment transport model implemented within the Proudman Oceanographic Laboratory Coastal Ocean System (POLCOMS). An unlimited number of sediment classes can be transported both as suspended load and bed load. Suspended sediment concentration is calculated following advection-diffusion schemes similar to those used for other scalar quantities. The location of the sediment bed is obtained from near-bed sediment mass conservation and the sediment bed is represented in the model by a layered structure. The ability to reproduce suspended concentration profiles and morphological evolution for a simple case is tested against laboratory experiments of trench migration in a flume.