New study paves the way for improved nature-based coastal defences

Satellite image of the Pearl River Delta.
  • A study in the Pearl River Delta in China could greatly assist in providing much needed flood defences for major cities such as Guangzhou
  • Mangrove trees allow excellent protection, but scientists are now able to predict best location for them to provide maximum protection
  • First study to show how coastal mangrove trees can modify the movement of water in a river delta plain during extreme weather events like typhoons

Scientists from the National Oceanography Centre (NOC) have made a breakthrough discovery that could lead to significantly improved coastal defences using mangrove trees.

The study showed that mangroves – which are shrubs or trees that grow in coastal salt water, are effective at reducing the water level during extreme events such as heavy storms or typhoons.

While mangroves provide a layer of natural protection, the study also showed that, in order to utilise mangrove-based defences, location-specific numerical simulations are essential to effectively design them. The research was conducted across the Pearl River Delta in the South China Sea which is home to several Chinese “mega-cities” such as Hong Kong, Shenzhen, and Guangzhou. All three cities are currently experiencing huge growth which comes with an expansion of areas vulnerable to flooding.

Mangroves can provide coastal protection in the tropical, subtropical, and warm-temperate world. In the UK, other natural habitats, for example saltmarshes, could provide similar coastal protection benefits, but they are still poorly studied.

Dr Michela De Dominicis, Senior Research Scientist in the Marine System Modelling Group at the National Oceanography Centre and lead author on the study, said: “This is an important new study that helps in planning out effective nature-based coastal defences. Mangroves are a vital natural resource at our disposal to protect communities. Even if mangroves on their own do not fully block water flow, they can reduce the extent of the flooding or they can be combined with traditional flood defences such as seawalls and levees, allowing for lower structures.”

The study is especially valuable given that existing research into the controlling factors of how coastal vegetation can reduce extreme water levels is unclear. This means that until now, there has been a limited implementation of using nature-based coastal defences in delta areas housing large cities.

Overall, the study found how effective mangroves are as a nature-based tool to protect coastal areas, as well as highlighting the need for location specific predictions to be made prior to extensive restoration efforts. The study, which was the first of its kind, will inform future research that will consider the amount of storm surge reduction that would make implementation of mangroves a viable investment, as well as considering the other benefits that mangroves offer such as carbon storage, biodiversity and the prevention of coastal erosion.

Dr Michela De Dominicis added: “This study clears up how mangrove forests change the movement of water in a complex delta plain on a local scale and in areas further away. Mangrove forests are one of the most powerful natural tools we have to protect coastal communities from rising sea levels and severe storms.”

Read the full paper in Nature