BREACHING VULNERABILITY OF COASTAL BARRIERS UNDER EFFECTS OF TROPICAL CYCLONES: A MODEL STUDY ON THE HUE LAGOON-VIETNAM

摘要

Under effects of tropical cyclones, the coast is subjected to attack both by surge and wave from the sea and by flooding from the bay. These forces pose a serious breaching threat to natural sea-defence works such as barrier spits, barrier islands, lagoon barriers, etc. on the coast. Unintended breaching can be catastrophic, causing losses of human life and damages to infrastructures and to natural habitats. Understanding of coastal breaching and breaching potential during tropical cyclone events is therefore of great importance to the management of coastal flooding hazards as well as to the design of sea-defence works. In this paper, a model study on breaching vulnerability of the coastal lagoon barrier of Hue-Vietnam during the historical event of the tropical cyclone in 1999 is presented. In spite of scarceness of available data, attempts were successfully made to simulate the barrier profile response and the barrier breaching process under this extreme condition. It is learnt that seaward erosion and severe wave overwash on coastal barriers during storms can considerably narrow and lower the barrier profile and thus exaggerate significantly the barrier breaching potential. The model predictions for the barrier response to wave overwash and the time-dependent breach growth seem realistic and in agreement with available observation data.