189 / 2024-02-27 11:11:36

Coastal compound flood modeling and analysis for a low-lying region of Hong Kong

Urban flooding,flood hazard,rainstorm,storm surge,compound flooding,drainage system

Coastal cities have become highly vulnerable to pluvial flooding because of the compound effect of rainstorms and storm surge events with rapidly changing climate conditions. In late 2023, Hong Kong witnessed three major rainstorm events with higher return periods (i.e., 100 ‒ 500 years), causing severe socio-economic damages to the local government and public properties. Urban flood modeling at a finer scale (i.e., 1 meter or less) of highly densely populated coastal regions with complex infrastructure systems and topography is one of the biggest challenges, because of the limited availability of information on underground drainage systems and computational costs. A coupled modeling package of stormwater management model (SWMM) and LISFLOOD-FP is employed for modeling of 1D underground urban drainage system and 2D overland flooding of Heng Fa Chuen area, a case study of Hong Kong. The integrated modeling framework was calibrated and validated based on flood depth and area measurements.  The flood hazard of the region is evaluated under different rainstorm and storm surge scenarios with separate and compound conditions, and further investigation was made based on delineated flood zones. Results of the case study concluded that the rainstorm-based floods impacted more underground mass transit railway stations (i.e., MTR) and local residential buildings compared to high-rise highways and mountainous regions. Furthermore, the infrastructure systems and residential buildings located neighboring to the shoreline are highly impacted by storm surge-induced flooding. Also, compound flood events produced more damage compared to flooding that occurred either by rainstorms or storm surges individually. The capacity of existing urban drainage systems and shoreline protections need to be upgraded as potential mitigation measures to avoid future disruption in transportation systems, and the potential reduction of future flood risks to local residents and their properties during upcoming rainstorms. The methodology and findings discussed in this study can be generalized to other regions with similar topography, underground drainage systems, and climate conditions.