Abstract: Typhoon can cause storm surge and strong waves. Since the reclamation projects are built on soft soil foundation, which may cause the seawall subsidence. In that case, disaster strikes when the strong waves cause sea dike breaching and seawater pours into the reclaimed area. An improved numerical method based on classic staggered grid was introduced in this study. In flow expansions, a numerical approximation was applied that was consistent with conservation of momentum, and in flow contractions, a numerical approximation was applied that was consistent with the Bernouilli Equation. The flood evolution model of Zhoushan Donggangxincheng was established, and the evolution process of the flood and breach under Probable Maximum Storm Surge was calculated. The results show that orographic terrain plays a decisive role in the evolution process and final distribution of the flood. The range and degree of influence differs when fissure occurred in different location. Almost the entire southern region of Donggang can be affected by a 50-metres-wide fissure nearby due to the low terrain and lacking of large-scale artificial lakes, while the influence in the northern area is limited due to the relatively high terrain.

Key words: Donggangxincheng, typhoon, sea dikes breaching, flood evolution, numerical simulation