海岸侵食について

Abstract

Recently methods of prediction and prevention of beach erosion have been so strongly expectedthat a brief report on this problem is herein described from the view point of the mechanics of sedi-ment transport by fluid motion. A synthetic attempt is made to the mechanics of sediment transportsuch as the sediment threshold, rates of sediment transport and longshore sand drift, and momentumequations of sediment transport, on the basis of the mechanics of saltation of sand grains. Fromthis, a new formulation of longshore sand drift is made by use of this sediment transport law andthe theory of longshore currents by Longuet-Higgins.A theoretical, one-dimensional approach is also made for prediction of beach changes bycoastal structures and due to decrease of sediment input from a river. It should be noted thatthis approach is practically applicable for the prediction of beach change, but two-dimensional onescan be still expected owing to the existence of offshore and onshore sand transport in nearshore zones.In addition, some comments on beach erosion control are described for new applicable methodssuch as headland defense and sand filter systems, based on the intensive functions of natural sandybeaches in wave energy dissipation.