Quantitative Evaluation of Controlling Effect of Headland on Longshore Sand Transport Using Model for Predicting Changes in Contour Lines and Grain Size

On Oharai Beach, a large amount of sand has accumulated owing to the formation of a wave shelter zone of the port breakwater, causing excess deposition in the navigation channel, whereas severe beach erosion has occurred south of Oharai Port. With these large-scale beach changes, the grain size of the seabed materials has significantly changed, and the area covered with coarse sand has been expanding. Simultaneously, the catch of Japanese hard clams, the habitat of which lies in a seabed composed of fine sand, has decreased. A model for predicting the changes in contour lines and grain size was applied to Oharai Beach; the controlling effect on longshore sand transport of an artificial headland was quantitatively evaluated in terms of beach and grain size changes, and the optimum depth of the headland was determined.