Storm surge modelling for Vietnam's coast

Vietnam is located near the Northwest Pacific Ocean - the largest storm basin of the world. Thus, Vietnam's coast with many coastal works, economical zones as well as high density populated regions, is the most vulnerable area under typhoons accompanied with serious storm surges. This is the main reason for the huge damages occuring in the areas. Storm surges threaten not only safety of people's lives but also coastal structures. Traditional planning, design ofcoastal projects and coastal zone management usually take into account these effects based on their probability distribution of very limited observed data, which results in a low reliability and safety. Therefore, improving the accuracy in determination of these abnormal water level rise during storm is essential for proper planing, design of coastal works as well as integrated coastal zone management. The objectives of this study are: (1) Set up a storm surge model for the Vietnamese coast; (2) Compute storm surges and determine the probability distribution of storm surge for the Vietnamese coast. To achieve these objectives, firstly various models of typhoon wind and pressure are investigated. Based on observations and criteria of root-mean-squared error, the Fujita model is selected for describing typhoon pressure field and the modified Rankine vortex model is chosen for presenting typhoon wind field. Secondly, Delft3D-FLOW is used to simulate storm surge in typhoon condition. The model is set-up for the northern part of the Vietnamese coast where high frequency of storm causing serious storm surges and severe damages occur. The hydrodynamic model is calibrated and validated for both nonstorm condition and extreme condition of typhoons. The effects of boundary conditions and model parameters to the results are evaluated using sensitivity analysis. Thirdly, based on storm track information, storm surges at various locations along the north coast are computed for the years from 1951 to 2001. And then, some popular statistical distributions such as log-normal, Pearson type III, general extreme value, etc. are used to fit with set of storm surge result to model the probability distributions of storm surge and to extrapolate for long-term return period values of storm surge at these locations. Finally, by evaluation the accuracy of the result for storm surge hind-cast, some suggestions is given for storm surge forecasting in the area