Sediment Grain Size Distribution behind a Detached Breakwater in Bengkalis Island Indonesia

摘要

Sediment is a fragmented material, primarily formed by the physical andchemical disintegration of rocks from the earth`s crust. These particlesrange in size from large boulders to colloidal size fragments and vary inshape from rounded to angular and vary in specific gravity, and mineralcomposition (Rijn, L. C. V. 1993). Sediment materials are classified andnamed based on their grain sizes. In a tropical peat coast, the sedimentconsists of sand, mud, and peat debris. The distribution of these grainsize becomes very important because it connects to the sedimentdepository behind detached breakwater which leads to the recoveryprocess of coastal erosion (mangrove replanting activity).This paper discusses the sediment grain size distribution behind detachedbreakwaters from the assessment of the field activity and numericalapproach. The existing detached breakwater that was installed at thenorthern part of Bengkalis Island is called the Selatbaru coast. Themeasurements are based on geo-informatics composed of both terrestrialsurveys and photogrammetry. For grain size measurement, we usedimage analysis and laser analysis methods.A 1D cross-shore profile model of Xbeach was chosen. The model usedthe option to define spatially varying sediment grain size. With thisfeature, it becomes possible to simulate the beach profile response towave and tidal action in a variety of grain sizes. Analyzing therelationship between the field activity and numerical calculation ofsediment grain size distribution will help determine recovery process tocoastal erosion especially in the tropical coast of Bengkalis Island,Indonesia.