Modelling mangroves as coastal protection
JBPacific is continuing to incorporate the latest research within our coastal modelling to characterise the effect of mangrove forests on reducing waves and storm surge. The complex matrix of mangrove roots and branches has a dissipative effect on incoming wave and surge energy. The XBeach model includes short-wave dissipation and flow interaction through coastal vegetation which is implemented by parameterizing roots, trunk and branches by their density, height, nominal diameter, and drag coefficient.
We have been calibrating the default XBeach model parametres to match field measurements conducted within mangrove forests in Vietnam. Field testing conducted by Bao (2011), among others, was undertaken to measure the decay of wave height as they passed through a mangrove forest in South-East Asia, which showed a reduction between 40% and 80% through 100m of mangroves. By varying our model parameters for our sites in North Queensland, we were able to achieve a mid-range result of 63% wave reduction over the initial 100m of mangroves.
This is important validation for coastal engineers looking to design nature-based coastal defenses. To get a required standard of protection, we need to consider the type of mangrove, the density, age, width and eventual size of the forest. Whilst this is a good start, we are still only calibrating our models on international data – so it would be a great university project to undertake similar in-situ wave measurements through different Australian mangrove forests.
With the threat of sea level rise and increasing population density in coastal areas, the preservation and expansion of these mangrove forests may an important factor in reducing coastal flood risk.
 Bao, T.Q. (2011), Effect of mangrove forest structure on wave attenuation in coastal Vietnam. Oceanologia, 53, 807-818