ABSTRACT

In this study, characteristics of river mouth topography generated by" waves and wave-induced current was first investigated through movable bed experiments. Then we examined applicability of two numerical procedures for predicting topography change around river mouth, that is, a modified one-line theory and a 3-D topography, prediction model. By comparing numerical and experimental results, it is found that modified one-line theory can apply for predicting bar formation of the small scale under the condition of a deep water depth at the river mouth and small wave incidence. On the other hand, change in water depth around river mouth calculated by the 3-D topography prediction model coincides well with the measured change in water depth provided that the interaction among topography change, wave transformation and change in wave induced current is taken into account properly.

1. Introduction

Coastal erosion has been a serious problem for recent years. It is said that the amount of the area lost from the near shore region is more than 160 hectare / year in Japan (Tanaka et al., 1993). One of the most plausible agency for this erosion is the decrease in the volume of discharged sediment from the river due to the construction of various structures such as dams and reservoirs along rivers and improvement of river channel for preventing land from disaster such as flood and utilizing flesh water for agricultural, industrial use. River mouth is interface of river and sea. Bed material is moving constantly, and it creates various types, of river mouth topography. Blockage of river mouth and shoaling of fairway often take place by such sediment transport. It is necessary, to comprehend the hydraulic function and role of the river mouth in sediment budget in coastal region around the river mouth.

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