Integrating Tidal Influence in Riverine Flood Hazard Assessment for Bridge Infrastructure: A Case Study on the Impact of Industrial Development in the JIIPE Economic Zone, Indonesia
Abstract
Coastal industrial zones in Indonesia are increasingly exposed to compound flood and sediment hazards driven by interactions between upstream discharge and tidal dynamics. This study aims to evaluate the extent of flood inundation and sediment transport processes in the Tanggok and Mireng sub-watersheds, which drain into the Java Integrated Industrial and Ports Estate (JIIPE) in Gresik, East Java. High-resolution Planet Labs satellite imagery (3 m x 3 m), government shapefiles, and Google Earth Pro data were used to generate land-cover maps via Maximum Likelihood Classification (MLC), and the maps were validated using confusion matrix analysis and the Kappa coefficient. Weighted composite runoff coefficients were derived in accordance with the Indonesian National Standard (SNI 2415:2016). Two-dimensional hydrodynamic and sediment transport simulations were performed using HEC-RAS 2D under a 100-year return-period discharge scenario, combined with two tidal boundary conditions: the highest tide (+2.73 m) and the lowest tide (+1.44 m). Land cover classification achieved Kappa coefficients of 0.651 (Tanggok) and 0.557 (Mireng), yielding weighted runoff coefficients of 0.60 and 0.64, respectively, reflecting high flood susceptibility dominated by aquaculture ponds, residential areas, and barelands. Simulation results show that the highest-tide condition increased flood inundation depth to beyond 2.0 m in low-lying zones adjacent to bridge structures. Peak flow velocities exceeding 2.0 m/s were recorded near bridge pier locations under the lowest tide condition, indicating significant scour potential. Tidal backwater effects at the river confluence induced cyclic deposition and scour phases around bridge foundations, posing structural risks to critical infrastructure. These findings demonstrate the value of integrating remote sensing and 2D hydrodynamic modeling for infrastructure-sensitive flood risk assessment in tropical coastal watersheds. Future research should incorporate climate change projections and sea-level rise scenarios to strengthen long-term disaster risk management in coastal industrial regions.