Evolution of the Porong River Estuary, Indonesia: Morphological Changes of Lusi Island through Sediment Modeling and Time-Series Interpretation of MNDWI

Abstract A sedimentation issue in the estuary of Porong induced by Lapindo hot mud discharge had caused a significant morphological alteration. This study aims to determine the geomorphological evolution in the Porong Estuary and the geochronological formation of Lusi Island. This study employed a numerical modeling approach, consisting of flow and sediment transport modeling modules (Delft3D-FLOW and Delft3D-SED), with a curvilinear grid resolution of 25–50 m over a 5 × 6 km domain. A satellite imagery processing was also performed using multitemporal Landsat data (2000–2024) analyzed using the Modified Normalized Difference Water Index (MNDWI), followed by binary classification and vector digitization. The results show that sediment accumulation of ± 0.06 m in 15 days, increasing to over 1 m after four years (MORFAC 96), with land expansion confirmed by satellite data from 6.29 hectares in 2000 to 147.86 hectares in 2024. Of particular concern, the increasing sediment thickness from 0.0026 m to 0.38 m over a 14-year equivalent simulation suggests a sustained process of geomorphological development. The findings of this study emphasize significant sedimentation trends and the dynamics of the estuarine environment in the Porong Estuary. It is, therefore, crucial to implement coastal hazard mitigation strategies, effective land use planning, and environmental monitoring to minimize further environmental degradation resulting from excessive sedimentation.