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This paper presents a scenario-based study that investigates the interaction between sea-level rise and land subsidence on the storm tides induced fluvial flooding in the Huangpu river floodplain. Two projections of relative sea level rise (RSLR) were presented (2030 and 2050). Water level projections at the gauging stations for different return periods were generated using a simplified algebraic summation of the eustatic sea-level rise, land subsidence and storm tide level. Frequency analysis with relative sea level rise taken into account shows that land subsidence contributes to the majority of the RSLR (between 60 % and 70 %). Furthermore, a 1D/2D coupled flood inundation model (FloodMap) was used to predict the river flow and flood inundation, after calibration using the August 1997 flood event. Numerical simulation with projected RSLR suggests that, the combined impact of eustatic sea-level rise and land subsidence would be a significantly reduced flood return period for a given water level, thus effective degradation of the current flood defences. In the absence of adaptation measures, storm flooding will cause up to 40 % more inundation, particularly in the upstream of the river. [ABSTRACT FROM AUTHOR]

Huangpu River floodplain is historically vulnerable to flooding due to its location in the path of tropical cyclones, low elevation, relatively flat topography, rapid changes in sea level and fast rate of land subsidence due to urbanization. This paper presents a scenario-based study that investigates the fluvial flood potentials in the Huangpu River floodplain. Flood scenarios with return periods of 50, 100, 200, 500 and 1,000 years were designed to cover the probable situations. Further, a flood inundation model (FloodMap) that tightly couples a river flow model with a 1D solution of the full form of the St. Venant equations and a 2D floodplain flow model was used to predict the river flow and inundation extents. Flood characteristics obtained from the simulations were used in the exposure analysis to determine the spatial distribution of susceptible land uses under different scenarios. Results suggest that overtopping inundation mainly occurs within 1-2 km of the banks of the Huangpu River, with larger inundation extent predicted in the upper and middle reaches of the channel, a result of varying protection levels from relatively rural upstream to high urbanized floodplain in the vicinity of the middle reaches. [ABSTRACT FROM AUTHOR]