AIMS AIMS/IBM Wave Attenuation in Mangrove Forests

Mangroves are densely vegetated mudflats that exist at the boundary of marine and terrestrial environments. They play an important role in estuarine and nearshore ecosystems and their densely interwoven trunks and roots provide a vital habitat for many marine and terrestrial organisms. Mangroves also act to trap and stabilise sediment and reduce the risk of shoreline erosion due to their ability to dissipate surface wave energy. It is this attribute which makes mangroves a potential natural solution for particular coastal protection problems. However, because of the random, complex nature of mangrove trunks and roots (Figure 1), the transmission of waves through mangrove forests is still poorly understood, but recent work has begun to address this problem. Field observations of surface wave attenuation in mangrove forests were undertaken in both Townsville, Australia and on Iriomote Island, Japan.
High resolution wave gauges were deployed throughout the mangroves along a transect in line with the dominant direction of wave propagation.	Figure 1: The random, complex geometry of mangrove trunks and roots.
Data gathered was used to verify a numerical model of wave attenuation. The numerical model is based on the fact that surface waves propagating within a mangrove forest are subject to substantial energy loss due to two main energy dissipation mechanisms; multiple interactions of wave motion with mangrove trunks and roots, and bottom friction. The dissipative characteristics of the mangrove forest are estimated from the observed physical parameters such as trunk diameter, spatial density and vegetation structure, which are not necessarily vertically and horizontally uniform. The resulting rate of wave energy attenuation depends strongly on the density of the mangrove forest, diameter of mangrove roots and trunks, and on the spectral characteristics of the incident waves.