Coastal Zones

Biography

Biography: Prof Takao Yamashita

Abstract

Quantitative understanding of cross-shore and longshore sediment transport system is essential information in carrying out coastal protection. Regular measurements of shoreline and the beach profile changes enable the estimation of nearshore sediment distribution by integrating the sediment budget from the clear lateral boundary conditions (such as the fixed boundary conditions of zero sediment transport) and cross-shore sediment transport rate obtained from the beach profile changes. However this method needs the high accuracy measurement of beach topography. Another way of estimating the nearshore sediment transport distribution is using the breaking wave energy distribution in the surf zone. In this method, it is necessary to determine the coefficients for associating breaking wave energy dissipation and sediment transport rate. Assuming equilibrium beach profile, the coefficients can be determined from sediment transport rate distribution that can explain the measurement results of the shoreline changes. In this wave energy method, incident wave energy flux is commonly computed by the wave height and breaking wave angle at the breaking point estimated from the water depth ratio. However, this method does not take a bore energy dissipation in the surf zone into account. In recent years, a third-generation spectral wave model in shallow waters such as SWAN has been put into practical use, it has become possible to simulate the propagation of shallow waters irregular waves in consideration of the energy dissipation characteristics due to depth-induced wave breaking. It has become possible to reproduce the surf zone energy dissipation of bore by using the output of SWAN’s depth-induced breaking energy dissipation rate ( ) to estimate the sediment transport rate in the surf zone. This study proposed the method of sediment transport estimation using and applied it to the annual sediment transport analysis in a pocket beach.