Abstract
Low-lying coastal regions and their populations are at risk during storm surge events and high freshwater discharges from upriver. An integrated storm surge and flood inundation modeling system was used to simulate storm surge and inundation in the Tsengwen River basin and the adjacent coastal area in southern Taiwan. A three-dimensional hydrodynamic model with an unstructured grid was used, which was driven by the tidal elevation at the open boundaries and freshwater discharge at the upriver boundary. The model was validated against the observed water levels for three typhoon events. The simulation results for the model were in reasonable agreement with the observational data. The model was then applied to investigate the effects of a storm surge, freshwater discharge, and a storm surge combined with freshwater discharge during an extreme typhoon event. The super Typhoon Haiyan (2013) was artificially shifted to hit Taiwan: the modeling results showed that the inundation area and depth would cause severe overbank flow and coastal flooding for a 200 year return period flow. A high-resolution grid model is essential for the accurate simulation of storm surges and inundation.
Highlights
Typhoons frequently cause major damage in Taiwan and can combine with storm surges and river flows to produce coastal flooding
Storm surges correspond to abnormal variations in the free ocean surface that are driven by atmospheric forcing from extra-tropical storms and typhoons [1]
When a storm surge occurs at the Tsengwen River mouth and meets the high water level in the river, the water cannot drain into the coastal ocean, resulting in severe flood inundation in the lowland region [32]
Summary
Typhoons frequently cause major damage in Taiwan and can combine with storm surges and river flows to produce coastal flooding. The strong winds and low atmospheric pressure of a typhoon approaching Taiwan often cause storm surges that can severely damage coastal areas, especially the low-lying lands near river mouths because of the dual effect of river flooding from typhoon-brought rains and backward uplifting seawater floods from storm surges [5]. A reliable model needs to be developed to predict the coastal inundation from the interaction between typhoon-induced storm surges and river flows to facilitate coastal management and hazard mitigation. The primary objective of this study was to apply a three-dimensional hydrodynamic model with an unstructured grid to simulate inundation patterns in the Tsengwen River basin and the coastal region in southern Taiwan resulting from the interaction between a storm surge and the river flow during typhoon events.
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