Land Flooding

Intense and prolonged rainfall over coastal areas generates significant surface runoff that flows directly into coastal waters, carrying land-derived materials from the surrounding landscape. These materials typically consist of humus, soil particles, and sediments eroded from the land surface. In addition to transporting suspended materials, surface runoff introduces large volumes of freshwater into the coastal environment. This freshwater input alters the physical characteristics of coastal waters and influences the surrounding ecosystem. Once discharged into the sea, coarse particles settle rapidly on the seabed, while finer sediments remain suspended and can be transported considerable distances offshore by coastal currents.

Coastal areas without river inflows are generally dominated by coral reef ecosystems. In these environments, reductions in salinity caused by freshwater inflow, together with increased concentrations of fine suspended sediments, can severely stress coral reefs and indirectly disrupt the habitats and biological communities they support. In contrast, estuarine environments with river mouths are commonly dominated by mangrove ecosystems, which are naturally adapted to freshwater inputs and suspended sediments. Furthermore, in low-wave-energy coastal environments, sediment accumulation may lead to shoreline morfological changes and seabed shallowing. These morfological changes modify local water circulation patterns, which can subsequently influence coastal ecosystem structure and ecological processes.

Advanced numerical modeling provides an effective scientific tool for evaluating the impacts of freshwater inflow and sediment transport resulting from surface runoff. Integrated modeling scenarios simulate the entire process, beginning with surface runoff generation and continuing through changes in coastal circulation, water levels, and sediment and particle transport within the receiving coastal waters.

The Land Flood Model simulates rainfall-runoff processes and overland flow across the watershed. The outputs from this model are subsequently used as input for the Hydrodynamic Model, which simulates changes in coastal circulation patterns and water levels. The transport, dispersion, and deposition of sediments and other particles entering coastal waters are then simulated using the Bottom Sediment Transport Model, Suspended Sediment Transport Model, and Particle Tracking Model.