Many cities in Vietnam are located at the coast and are exposed to heavy weather events that yearly causes casualties and economic losses. At the same time the country is developing rapidly and thus more space is allocated to accommodate urban growth. Studies have shown that there are cases in Vietnam were residential expansions have led to an increase in risk of pluvial flooding. This type of flooding is caused by insufficient capacity of the urban drainage system as a result of heavy rainfall.

Keeping in mind the exposure of flooding in Vietnam and the potential of SUDS to provide flood risk reduction, it is desirable to set general design guidelines with respect to urban drainage. On top of that, 1D/2D hydrodynamic models have proven to be useful when mapping flood risk at different scales. Therefore, this study aims to show how 1D/2D hydrodynamic models can be put into practice when designing drainage infrastructure and implementing flood adaptation measures. For this research, hydrodynamic modelling tool Delft 3D-FM (D-HYDRO) was implemented in the drainage design of Hà Nam island in Quang Ninh province.

This study provides predictions of pluvial flooding for the future development scenario of Hà Nam island. Based on the 2023 masterplan, all projected land use and terrain changes have been incorporated in the 1D/2D hydrodynamic model. Hà Nam island currently discharges it’s stormwater by means of sluice gates that can only be opened during low tide. Based on sea level rise predictions, it is estimated that the probability that Hà Nam receives rainfall during high tide will increase the coming decades. Therefore the urban drainage design considers extreme rainfall events during which the area can only be drained by means of pumping stations. Based on the modelling study, it is concluded that the existing residents of Hà Nam will face an increased risk of pluvial flooding in the future development scenario. This study proposes the implementation of two types of SUDS to increase local stormwater storage, namely vegetated swales and park overflow zones. It was found that these do result in flood risk reduction, but still leave current residents of Hà Nam vulnerable to flooding during extreme rain events. This study recommends making modifications to the 2023 masterplan, emphasizing the safety and wellbeing of Hà Nam residents.