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Hydro-oceanographic characteristics and sedimentation in the waters of Kemujan Island, Karimunjawa, Indonesia

Kemujan Island is one of the tourist destinations located in the Karimunjawa Islands in the Java Sea. This island’s beach sands and aquatic resources have not yet been fully studied. Its coastal conditions are strongly influenced by hydro-oceanographic factors such as waves, currents and tides that can affect biotic and abiotic ecosystems, including bottom sediments’ characteristics and movements. This study aimed to analyse the oceanographic factors and sediment movement in the waters of Kemujan Island, Karimunjawa. The research was carried out in two stages: sediment sampling and oceanographic data measurement in the field, and sediment sample analysis conducted at the laboratory. The methods used in this research are quantitative. Based on the sediment texture distribution analysis, the sediment type in the waters of Kemujan Island is dominated by medium to fine sand with grain sizes ranging between 0.5-0.125 mm. The surface current speed ranged from 0.04 to 0.25 m s, the bed shear stress ranged from 0.0606 to 0.0151 N m and the shear velocity ranged from 0.7658 to 0.3829 cm s. The oceanographic factor that affects the transportation of sediments is the current and weak current conditions affect the ability of the sediment particles to settle. Based on the results of the calculation of bed shear stress and shear velocity, the shear stress at the seabed is related to the speed of the water current. The shear stress exerted on the seabed sediment is not adequate to move sediment grains dominated by fine to medium sands in the waters of Kemujan Island, Karimunjawa.