Assess the Typhoon-driven Extreme Wave Conditions in Manila Bay through Numerical Simulation and Statistical Analysis

Abstract

Philippines is the most exposed country in the world to typhoons, with an average of twenty tropical cyclones entering the Philippine Area yearly. This study develops numerical models to simulate the extreme waves driven by typhoons, in an attempt to provide design wave conditions for a hypothetical land reclamation project in Manila Bay. A total number of 36 tropical storms passing through Manila Bay are selected within a 200 km search radius of the project for the period from 1977 to 2016. The typhoon-driven storm waves in Manila Bay are then simulated using a third-generation spectral wave model, driven by a hybrid wind field which combines both the typhoon information from JTWC (Joint Typhoon Warning Center) and the background information from CFSR (Climate Forecast System Reanalysis). A nested wave modelling scheme is adopted, which comprises of a regional wave model and a local wave model. The regional wave model encompasses all the typhoon tracks of the selected tropical storms, providing the wave inputs (spectrum) at the boundaries for the local wave model which covers the Manila Bay with a focus on the project locations. Model results of the maximum significant wave heights Hm0, the associated mean energy wave period Tm-1,0, and wave direction at the project locations are extracted from the numerical simulation. Extreme value analysis is finally conducted, using the moment ratio diagram to select the best distribution functions, to determine the extreme wave conditions corresponding to different return periods.