It is possible to prevent or, at least, slow down the erosion of some coastlines. Groynes help to prevent longshore drift; while trees and grasses can be specially planted to stop sand dunes being blown away. Sea walls help to prevent coastal erosion and protect low-lying areas from flooding.
As sea levels rise and coastal communities face the threat of erosion and flooding, coastal defence structures, often built with concrete, have become the norm in many parts of the world.
But these hard engineered structures, like seawalls, breakwaters and groynes, are both expensive and bad for the environment. Our team of University of Melbourne scientists is joining a growing number of international researchers looking at whether natural coastal defence structures could be a better option. We are trialling mussel reefs and mngrove forests in Melbourne’s Port Phillip Bay to see how well they protect our shorelines.
Natural coastlines have in-built coastal defence in the form of sand dunes and beaches, saltmarsh, mangroves, seagrass and kelp beds, and coral and shellfish reefs. These natural structures can reduce the height of waves as they approach the shore and trap sediment, increasing the height of the land relative to sea level. This reduces flooding and erosion. Mussel reefs and mangrove forests are particularly important in Port Phillip because they are native habitats that have suffered significant declines historically. We are creating the mussel reef from recycled shell and natural basalt rock, and we expect it to reduce wave height and promote accretion of the eroding foreshore.
For the mangrove forests we will use a ‘hybrid’ approach, which involves planting the mangroves within concrete cultivars that attenuate waves, accrete sediment and provide the right conditions for the forests to grow. Elsewhere, other natural habitats are being used to protect shorelines. For instance, in the United States, oyster reefs have been widely restored on the east coast to provide erosion control. Oysters need something hard to attach to, and lots of creative reef designs have been engineered to replace lost habitats and enhance oyster populations.
In contrast, artificial structures are expensive to build and maintain and cause significant ecological damage. In particular, they lead to a loss of biodiversity through the replacement of natural habitats and are often hotspots for invasive species.
Picture Credit : Google