Land Subsidence Effect on Coastal Sediment Transport pattern in Pekalongan Beach, Central Java - Indonesia

Abstract

<p>Pekalongan Beach, lying on the northern part of Java Island in Indonesia, is one of the main cities in Central Java because it is famous for its traditional craft, especially batik. has suffered from coastal flooding and abrasion over the last ten years. This disaster is getting worse due to the significant impact of land subsidence. This study examines sediment transport conditions on the Pekalongan coast using field observation data and a numerical model computation using the Delft3D Flow model. The research was started by collecting and analyzing primary and secondary field data. After the model was calibrated to tidal water level elevation and current velocity field data, hydrodynamic and sediment transport simulations for two scenarios representing the conditions before land subsidence in 2016 and after subsidence in 2021. The input land subsidence rate was assumed based on the recent data at a station 10 cm/year. Sensitivity analysis was carried out to examine which input parameters most sensitive to coastal sediment transport conditions. In the sensitivity analysis, various sediment grain size, wave height and wave direction were used in the numerical model. It is found that sediment grain size is the most sensitive effect on sediment transport condition. The simulation results indicate that the sedimentation rate increased by 56% after land subsidence. In contrast, the erosion rate decreased by 4% after one neap-spring tidal cycle (around 15 days) in the study area. Coastal inundation in Pekalongan was getting worse due to land subsidence and higher wave condition in recent years.</p>