Integrating Catchment and Coastal Processes to Increase Flood Protection in Estuaries

Estuaries and surrounding coastal areas worldwide possess high ecological and socio-economic values, while they experience an increasing flood risk due to climate change that needs mitigation. There are a number of studies that examine probabilities and hydrodynamic behaviours of estuarine flooding accounting for sea level rise; however, they often overlook long-term variability in estuarine morphology, which will have a major impact on future flood hazards within estuaries. In order to mitigate flooding, a number of flood management practices have been applied to estuaries and catchments, yet those influence on long-term estuarine morphodynamics is barely assessed, and feedback on future flood hazards needs to be better understood. There is a need for a tool that can assess climate change and human management factors on future flood hazards around estuaries. A novel modelling framework incorporating catchment hydrological (HEC-HMS), estuarine morphodynamic (CAMME), and estuarine hydrodynamic (Delft3D-FLOW) models has been developed and tested using various management and climate scenarios. This offers an integrated approach for the evaluation of a range of management applications at catchments and estuaries along with climate change on long-term estuarine morphodynamics and associated future flood hazards. The following three points are obtained as primary outcome of this research: (i) the influence of catchment management and climate change on estuarine morphodynamics can vary depending on relative hydrodynamic forces of tides and rivers; (ii) the long-term estuarine evolutions under SLR substantially alters future flood conditions within estuaries; and (iii) evolutions of managed realignment (MR) under SLR play a crucial role in determining a flood mitigation function of MR, considering a complex interplay between channel network developments within the realignment sites, remaining structures of breached seaward embankments, and overall estuarine funnelling factors. This research enhances understanding of the plausible system responses to expected changes, such as climate trends and human activities, which will provide a foundation for avoiding unanticipated consequences and guiding alternative policy options.