Ho Chi Minh City (HCMC), a low-lying and fast-growing metropolis of 7.4 million people, faces significant and growing flood risk. Periods of intense rainfall regularly inundate the city, as does riverine flooding from the Sai Gon River and neighboring Mekong Delta. Climate change may worsen these risks. Ho Chi Minh City ranks fourth globally among coastal cities most threatened by climate change, which may increase the frequency of intense rainfall and swollen rivers. Rising sea levels, as network boundary conditions, combined with land subsidence compound the threat.
The ambitious targets that are set out to sustain GDP growth will require a serious consideration of urban flooding, its associated impacts, and exposure to the population at risk, economic activities, infrastructure, built-up areas and associated health issues. Although several approaches have been carried out in the last years, a unique new study has been conducted in order to model the hydraulic context, including the river, urban drainage and wastewater systems. Thanks to his strong capabilities, PCSWMM has been selected to conduct the simulations.
The model has been developed on the Tham Long Ben Cat subcatchment in the northern part of HCMC. In order to address the various challenges, the model is taking into account (i) the climate change (ii) the land subsidence and (iii) the growing population.
The implemented methodology is based on various modelling scenarios that involve (i) other models interfaces, especially to define boundary conditions regarding the sea level and the stream flows (ii) hydrological and hydraulic 1D-2D modelling on a very large area (iii) the rainfall forecast regarding climate change (iv) the population forecast that is expected to impact the wastewater flows as well as the runoff flows through the runoff coefficient (v) the economic impact of floods (v) the possible hydraulics works costs.
The results of these modeling process allow the stakeholders to decide which solution was the most suitable. The optimal solution includes (I) separated networks for wastewater and storm sewers (ii) sluice gates at some critical canal locations (iii) significant pumping stations in order to keep the water level in the canal below a critical threshold.
The model was a key tool in order to make the optimal decision based a challenging multi-criteria analysis.
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