Understanding the significance of Coastal erosion pattern along Bengkalis Island due to climate change

Abstract Bengkalis Island is located on the outer border of Indonesia and faces the Malacca Strait. The northwest part of the island, which is predominantly composed of peat soil, was the most severely affected by erosion. The condition is particularly frequent during periods of high rainfall intensity due to climate change. This has caused the landslide towards the sea, triggered by land instability due to the land use changes and sediment transport in the nearshore area. Understanding the nearshore sediment transport is needed as a base to design proper coastal protection. To address this phenomenon, we investigate a model of the sediment transport pattern along the west coast of Bengkalis Island in low and high wave season using a coupled flow and wave model in Delft3D software. This model uses bathymetry data from BATNAS, waves and wind data from ERA-5, TPXO global tides, and sediment properties from secondary data. Model verification was conducted using tides recording data from Geospatial Information Agency (BIG) and field survey data of Yamaguchi University and Riau University. By examining the two cases, it was found that the northwest edge of Bengkalis was the more prone to erosion, whereas the southern side of the island was more likely to experience sedimentation, even if erosion also happens there during the low-wave season. Furthermore, the hydrodynamic conditions of the waters and land surrounding it, which contribute to landslides and coastal erosion, are considered in selecting the most suitable Nature-based Solution (NbS) for coastal protection.