INCREASE IN SEAWARD SAND TRANSPORT BY ROCKS BURIED UNDER FORESHORE OWING TO CHANGE IN SEEPAGE FLOW DURING WAVE RUN-UP

Abstract

 When impermeable objects such as beach rocks are buried under the beach face, the return flow and seepage flow during wave run-up may change, causing the change in sand deposition and erosion of the foreshore. In this study, such examples were shown, taking the beaches on the Komesu coast in Okinawa and on Hithadhoo Island in Maldives as examples. On the Komesu coast, coral reef well develops, and a sandy beach composed of gravel extends on the basement rocks. On the beach on Hithadhoo Island, beach rock with a slope of 1/7.5, the same slope as the foreshore slope of the coast, halfly exposed on the beach face because of erosion. Taking these examples into account, two-dimensional movable bed experiment was carried out to investigate foreshore changes under the condition that rocks are buried under the foreshore composed of gravel. It was found that seaward sand transport may accelerate when rocks exist under the foreshore.