Analytical and numerical simulation of tsunami mitigation by mangroves in Penang, Malaysia

The Andaman tsunami that occurred on 26 December 2004 killed about a quarter million people worldwide, of which 52 deaths happened in Penang, Malaysia. Mangrove forests fringing the shallow coastal seas of Penang Island and northwest of Peninsular Malaysia have been credited to have played a role in mitigating the tsunami waves. It is therefore relevant to assess the role of mangroves in tsunami mitigation by analytical model and numerical simulations. The role of mangrove forest in reducing tsunami wave energy, heights and velocities are simulated by the incorporation of the Morison Equation to represent friction provided by the mangrove forest for the coasts of Penang. Wave heights and velocities can be reduced in the presence of mangrove. However the degree of reduction varies significantly depending on several factors such as wave period and wavelength as well as mangrove characteristics including forest widths and density. For a wave of 10 km wavelength, with wave height and velocity of 1.0 m and 1.0 m/s, respectively at the shore without a mangrove forest, then a mangrove forest of 500 m width may provide a reduction ratio for wave height and wave velocity of about 0.55 and 0.50, respectively.