Storm Surge Risk Assessment of Tacloban, Leyte Using MIKE 21 Model Simulation of Typhoon Haiyan
Rehabilitation efforts for the destruction of Typhoon Haiyan which ravaged the central part of the Philippines may take up to 10 years and will cost PhP 250 billion (USD 5.7 billion). To prevent extensive damages and extreme cost for rehabilitation, thorough risk assessment along with systematic infrastructure plans, evacuation plans, and land use planning of the areas must be done. The study conducted a qualitative risk assessment for the city of Tacloban, one of the severely affected areas by the storm surges brought about by the typhoon. Its coastal areas are at high risk to storm surge due to: its location relative to the typhoon track; low elevation topography; dense population; and progressive economic activities. The risk assessment model proposed by the United Nations (1991) was used, where the risk index is defined by the hazard index multiplied by its vulnerability index. The risk index was evaluated into a five-point scale: very high, high, medium, low, very low. The storm surge hazard index of the study area was derived from the simulation results of Typhoon Haiyan event using MIKE 21 – a versatile software used for coastal modelling. Simulations were made using the coupled approach of Hydrodynamic Flexible Mesh (HD FM) and Spectral Wave (SW) models. This approach takes into account both surge water levels and wave crest heights for overtopping of coastal structures. The vulnerability index was determined from population, built environment, and critical service centers. The resulting risk index map will be beneficial to the on-going rehabilitation efforts in the study area.