Laboratory Study on Waves and Sediment Transport near Swash Zone by the Combined Short and Long Waves

Experiments with short waves long waves and their combined waves are conducted both on a fixed and on a movable bed. Water and sand surfaces are measured simultaneously by using a video technique. In the uniform depth area the combined waves are linear sum of the component waves as short waves show no reflection. On the slope particularly near the shoreline short waves break riding on the long waves together with considerable modulation which cannot be described by simple sum of component waves. Nor can be sediment transport rate. Sediment transport rate in the surf zone are evaluated for uprush and downrush respectively. Their amount is proportional to 3/2 power of Shields number with large scatter for the downrush the direction being onshore for the uprush and offshore for the downrush.