Assessment on the Characteristics and the Damping Performance of Coastal Forests in Pangandaran after the 2006 Java Tsunami

Abstract

The use of coastal forests as natural tsunami barrier has long been the source of controversies due to inconclusive understanding on the damping performance and contradictory field findings from the last tsunami events. After experiencing hundreds of casualties and severe destruction on the infrastructures due to the 2006 South Java Tsunami, the coastline of Pangandaran district in West Java was replanted by coastal forest vegetation to mitigate future tsunami as well as improving the quality of the environment. The design of coastal forests along the coastline of Pangandaran adopted divide-and-rule strategy concept. Considering their physical and biological aspects as well as the ability to withstand hydraulic forces. This concept requires different species at different locations perpendicular to the coastline with staggered formations in order to provide optimum damping performance of the coastal forests. Unfortunately, this concept has never been quantified or hydraulically tested against extreme cases like tsunami. The paper will present the characteristics and the latest conditions of coastal forests in Pangandaran including the problems and the challenge of this mitigation system in the last five years. Moreover, damping performance of the coastal forests was also investigated by means of Nonlinear Shallow Water Equation Model to quantify the contribution of coastal forest and other existing environmental aspects such as the bathymetry and the topography to the total tsunami attenuation. Based on the obtained wave transmission, the simulation analysis shows that the characteristics of bathymetry and topography along the coastline play significant role in reducing the impact of tsunami compared to the coastal forests.