| An important property of the sandy coast is its dynamic variation, the costal sediment moves with the usually changed condition of the wave and water flow, then causing the beach profile changed. A significant performance of the dynamic changes of the sandy coast is the changes between the storm profile and normal wave profile. So sandbar and berm are mainly manifestations on the motion of the coastal sediment. Study on the variation of the costal profile has great significance on investigating the change of sandy coast and the nature coastal protection.The physical experiment results of the motion of coast sandbar in the storm wave condition are invesigated, and the disappearance of the coast sandbar profile and the recovery of the berm profile under the normal wave conditions are discussed in this paper. The main content includes:(1) The effect of different flume widths (25cm,35cm,45cm and70cm) on the sandbar profile is discussed. Regular wave and wave group acting on the coast with the slope of1:10and1:20, the sandbar profile of the costal model appear the horizontal oblique along the width of the flume, the inclination decreased with the increase of the flume width, such as in case of H=9cm. And the effect of the flume width on the horizontal oblique are also discussed, the results showed that the wider of the flume the more severe horizontal oblique of the sandbar profile, it also affects the intense shock of the sandbar on the offshore and onshore movement. There is no horizontal oblique when the flume width is relatively narrow.(2) Study on the sandbar motion characteristic under the regular wave and wave group actions as the coastal slope is1:10and1:20. It indicates that the sandbar moves on the offshore and onshore directions, the shock motion frequency of the sandbar under the regular wave action is larger than that under the wave group actions; the shock motion frequency of the sandbar with the slope of1:10is larger than that of1:20. Both under the regular wave and wave group actions, the motion tendency of the sandbar is depend on the wave height, the sandbar moves on the offshore direction under the condition of large wave height, and with the decrease of the wave height, the tendency of the sandbar motion gradually moves on the onshore direction.(3) The disappearance of the coast sandbar profile and the recovery of the berm profile under the normal wave conditions are studied. The waves acting on the sandbar profile are the continual different critical normally wave conditions, and the action time of different wave conditions are determined by the steady terrain profile. The totally recovery time of the sandbar profile with the slope of1:10and1:20are13.5h and17.5h, and converted into the practical time are67.5h and87.5h, respectively. Study found that the sandbar did not move in the recovery process, but with the onshore motion of the sediment, the sandbar is gradually cut down and disappeared finally. The sandbar profile eventually restored to be a balanced profile with a berm. The experiment results showed that the slower coastal slope, the larger berm formed, and the better recovery effect.(4) For a further discussion of the characteristics of the balanced profile with different coastal slope and different flume width. It is found that the balanced profile only affected by the normal wave conditions, no correlation with the different wave conditions in previous storm period, and also no significant correlation with the flume width and the original coastal slope, the final balanced profile accord with the theoretical exponential curvature of coastal balanced profile. |
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