Assessing the coastal protection services of natural mangrove forests and artificial rock revetments

Coastal flooding and erosion cause significant social and economic impacts, globally. There is a growing interest in using natural habitats such as mangroves to defend coastlines. The protective services of mangroves, however, have not been assessed in the same rigorous engineering and socio-economic terms as rock revetments, and therefore are often overlooked by coastal managers. We used field measurements, a social science survey and economic valuation to compare the coastal protection services of mangroves and rock revetments, at five locations across Victoria, Australia. The results showed, in sheltered locations, both mangroves and rock revetments attenuated waves, however, the wave attenuation (per metre) of rock revetments was greater than mangroves, at two of the five locations. Only a small proportion of the survey respondents had observed flooding or erosion in their suburb but most agreed that mangroves provide important coastal protection benefits. Coastal landowners visited areas with mangroves more often than the public but were less likely to worry about the links between climate change and coastal erosion and flooding, or to agree that the coast was well protected with existing artificial coastal infrastructure, than other respondents. There were much higher up-front costs associated with building rock revetments, than planting mangroves, but rock revetments required less land than mangroves. Mangroves covered a larger area and averted more damages than rock revetments. Coastal managers and policy makers will have more success in advocating for nature-based solutions for coastal protection, if they are implemented in locations where they are eco-engineering and socio-economically acceptable options for climate change adaptation.