River Flooding

River systems collect excess surface runoff generated by heavy rainfall across a watershed. This excess water is transported downstream through rivers and eventually discharged into coastal and marine environments. Along with the water, various materials—both hazardous and non-hazardous—that have accumulated on the riverbed are carried downstream and deposited in estuaries. These materials commonly include chemical compounds associated with bottom sediments.

Throughout the river channel, high runoff generates intense turbulent flow, which continues downstream to the river mouth. Upon reaching the estuary, freshwater mixes with seawater, initiating complex physical, chemical, and biological interactions. These processes can significantly alter the natural equilibrium of the coastal environment. As a result, ecosystem cycles may be disrupted. In the short term, these changes can produce severe and potentially lethal environmental impacts, while long-term effects may permanently alter ecosystem structure and lead to the loss of biological communities.

To evaluate these processes, an integrated modeling framework is developed that begins with watershed (catchment) hydrology, continues through surface runoff and river hydraulics, and extends to estuarine and coastal hydrodynamics. The modeling scenarios incorporate rainfall intensity, runoff generation, river discharge, sediment transport, and the movement of dissolved and particulate materials carried by river flow. This integrated approach clearly illustrates the transport pathways and environmental impacts of freshwater inflow and associated materials, providing a reliable scientific basis for environmental assessment and decision-making.

The Land Flood Model simulates rainfall, infiltration, surface runoff, and overland flooding within the watershed. Its outputs provide boundary conditions for the River Flow Model, which simulates hydraulic processes throughout the river network. The Hydrodynamic Model then simulates water circulation patterns and water levels in estuarine and coastal waters based on river discharge conditions. Finally, the Bottom Sediment Transport Model, Suspended Sediment Transport Model, and Particle Tracking Model simulate the transport, dispersion, and deposition of sediments and other materials from the watershed through the river system and into the coastal ocean.