Simulation of flooding due to embankment breaches by Delft3D Flexible Mesh: Case study of coastal area in Shanghai

Simulation of flooding due to embankment breaches by Delft3D Flexible Mesh: Case study of coastal area in Shanghai

Yin, Jiangshan (TU Delft Civil Engineering and Geosciences)

Aarninkhof, Stefan (mentor)
Bricker, Jeremy (mentor)
Ke, Qian (mentor)
Visser, Paul (mentor)

Delft University of Technology

2020-05-25

As a low-lying city, Shanghai faces threats from typhoon and spring tide under the condition of climate change and land subsidence. With high water level at the toe, the sea embankment is likely to be overtopped and breached, finally resulting in inundation inland.  The objective of this research is to study climate change and land subsidence effects on Shanghai inland inundation due to dike overtopping and breaching under extreme weather condition.  A hydrodynamic model and a wave model have been established by Delft3D-FM and Delft3D respectively. Through validations on historical events, the hydrodynamic model and wave model are proved to be valid. The water level and wave condition along the coast, which are concerned as the results of these two models, are also essential inputs for overtopping and breach discharge calculation. In overtopping and breach discharge calculation, the threshold of breaching is estimated as an overtopping rate of 0.1 m3/m/s. The resulting overtopping and breach discharge gives the boundary condition of the overland simulation. The inundation map over Shanghai area can then be achieved by the overland simulation. A sensitivity analysis of the breach widths is also done.   Ten hypothetical typhoon events are provided by the Met Office Hadley Center under past and future climate conditions. These cases are applied to the whole process to study the effects of climate change on coastal flooding in Shanghai. The relative sea level rise is also considered for both past and future climate conditions.   The results show that places with high water level and low sea dike elevation are more likely to get high overtopping that can finally result in breaching. For Shanghai city, such vulnerable places can be found along Hangzhou Bay, especially in Jinshan District and the south-east corner of Shanghai. Besides, the entrance of Shanghai Yangtze River Tunnel is also vulnerable due to land subsidence. For some extreme cases, the whole Shanghai coast is in danger.  For the past climate and land elevation around the year 2000 with the wind speed return period of 1.3 yr and the breach width assumed to be 300 m, it is simulated that the maximum inundation area in Shanghai can be 1,805 km2 (33.3% of the simulated area in Shanghai). In the future, given the challenge of climate change and land subsidence, the sea level is relatively rising. The intensity of typhoon will generally strengthen. For the future climate and land elevation around the year 2100 with the wind speed return period of 4.5 yr, it is simulated that the inundation area in Shanghai can be 3,388 km2 (62.4% of the simulated area in Shanghai), which is almost twice of the inundation area around the year 2000.  The breach width also affects the inundation situation. If the breach width becomes larger, the inundation situation will be worse. However, as the breach width grows, the increase of the inundation area decreases.

Coastal flood modelling
Embankment breaches
Delft3D-FM
Shanghai
Climate change impact

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Student theses

master thesis

© 2020 Jiangshan Yin