Testing the effectiveness of hybrid infrastructural/nature based sand dune restoration as defence for an urban coastal community in Hong Kong

We document a hybrid infrastructural/nature based restoration of an artificial backshore dune in Big Wave Bay (Tai Long Wan), a small embayed sandy beach system in Hong Kong. The 2018 Super Typhoon Mangkhut destroyed the dune, believed to have been built by a coastal village community more than 80 years ago and had withstood all intervening storms. The destruction had itself illustrated how extreme events may alter landforms at a catchment scale, and the vulnerabilities of coastal communities that lies within the catchment. Subsequently, the Hong Kong government made a decision to 'hold-the-line' and rebuild defence in-situ, believed to have driven by space constraints, engineering philosophy, and/or public perception. The result may not be the most storm-proof, but it could be seen as the best outcome based on compromises, and could represent the most probable responses towards extreme events in urban coastal communities. Both hard engineering (in the form of concrete footslabs) and nature based approach (in the form of coastal shrub planting) were installed in 2021, and had shown different trajectory of change in the subsequent years. Although the defence mechanisms had not been tested in an extreme event, comparative strengths of the solutions could be surmised by their integration with the natural processes of the beach system. The overall cost effectiveness of this 'hold-the-line' strategy in Big Wave Bay is estimated, using potential land loss from sea level rise fed into a simple socio-economic model to predict potential economic loss. The result could shed light on quantifying the social costs for adaptation strategies in urban coastal communities in response to climate change.