FIELD OBSERVATION OF WAVES AND TOPOGRAPHICAL CHANGE NEAR THE SHORELINE SHORELINE

摘要

Good field experiment is needed to understand the (cross shore) beach process. Ultrasonic wave gages were deployed in the swash zone with small spacing for a few years. The gage detects either sand level or water level. Thus wave properties as well as profile change in the swash zone were measured continuously. Two cases of large-scale (berm) erosion are analyzed. 1) Shoreline erosion starts when high waves with significant power in long period (1 to 2 min.) waves reaches the top of well developed berm with help of rising tide. 2) During the erosion, beach level in the swash zone decreases uniformly, while bottom height just outside the swash zone is kept constant. 3) The erosion stops in a few hours as the berm is completely eroded or the swash slope becomes mild. From these results a speculation was made where long waves play dominant role in the swash zone dynamics.