Beach Processes of Shirarahama "a Pocket Beach"

Abstract

The objective of this paper is to make clear the mechanics of sand transport in Shirarahama "a pocket beach" in order to study beach processes of stable, natural sandy beaches. Seasonal changes of the beach are caused by incoming waves and by blown sands, but a little beach erosion has gradually occurred due to a lack of beach sediment by recent urbanization of the hinterland. Characteristics of the change in the beach sediment are made clear, together with the present situation of the main sources of beach sediment. A method for the prediction of beach change by blown sands is proposed on the basis of both the law of sediment transport and the equation of continuity for beach changes. Changes in the distribution of longshore wave energy flux along the shoreline instead of the total rate of sand drift are considered for long-term and short-term beach changes. It is concluded from this that this beach is stable for most of the year, but the beach sediment may be transported in the offshore direction at the both ends of the pocket beach for a very short period by high waves associated with typhoons and monsoons.