∣Exploring Nature-based Solution∣ Seawalls

As global temperatures and sea levels rise, more water management is needed, especially near coasts. A seawall is a type of structure used as a form of protection against high tides, tsunamis, storms, erosion, etc. Despite protecting people living near coastal areas, its intervention between water and land can disrupt ecosystem interactions. Concrete is used for approximately 70% of global coastal and marine structures. Furthermore, about 60% of China's coasts are lined with concrete for seawall construction. As a nature-based solution, living seawalls can serve as an alternative to conventional concrete sea walls.

Some nature-based solutions for seawalls are seagrass meadows, coral reefs, salt marshes, and mangrove forests. Solutions, such as living seawalls, can facilitate collaborative engagement with the natural environment. Amidst the continuing rise in global sea levels, conventional cement-based seawalls are increasingly inadequate in fulfilling the imperative for enhanced protective measures. In contrast, nature-centric solutions not only possess the inherent capacity to accommodate escalating water levels, but also dynamically evolve with the rising water levels.

Besides being a more efficient barrier, another benefit of it is that it can increase marine biodiversity. Traditional cement-based seawalls can destroy habitats and reduce the number of marine wildlife. For example, the Hong Kong Zhuhai Macau Bridge, built in 2018, requires the use of about a million tonnes of concrete. The construction of this bridge caused a loss of 60% of surrounding biodiversity in that area. Not only that, but it has also put one of their most endangered species, pink dolphins, under more risk.

Example Sea Wall Design by Reef Design Lab and SIMS

One type of sea wall currently under research and development is being conducted by the Sydney Institute of Marine Science (SIMS) and Reef Design Lab. They have created the Living Seawalls Initiative, which is a research project focused on creating designs to increase marine biodiversity around existing coastal infrastructures. Some aspects of their research include designing seawalls that imitate the structure of natural habitats of marine species to increase ecological value. Some of the designs are still made out of concrete, however, Goad, a designer from the Reef Design Lab, has said it was the only material strong enough to withstand the corrosive intertidal environment. Based on their test runs, these coral shaped seawall pieces are able to withstand 2 tonnes of pressure, while still keeping its shape. Even those these sea walls are still made out of concrete; the primary distinction is that they are artfully configured to foster the proliferation of marine life due to their coral-like structural design.

So far, Living Seawalls have been placed in two locations in Sydney Harbour as a test run. Within a few weeks, they have already developed algal and invertebrate growth. Continued research remains imperative for the evolution of seawall construction practices. These innovative designs could potentially advance conventional seawall construction methods, which can improve biodiversity preservation, while still providing an equivalent level of protection as conventional concrete seawalls. Furthermore, another aim of this project is to continue further research for of sustainable seawalls at a larger scale.

Mangrove Forest

Another nature-based solution for coastal protection are mangroves. Mangroves are a type of shrub or tree that grow along tidal estuaries. Indonesia has approximately 3.5 million hectares of mangrove trees and is home to one of the world’s largest mangrove forests. Mangrove forests function as natural seawalls due to their intricate root systems and dense vegetation, effectively absorbing and dissipating wave energy, thereby reducing the impact of coastal erosion and storm surges. Their ability to trap sediment further aids in shoreline stabilization, offering a valuable ecosystem-based defence against the forces of the sea. Unlike the project mentioned earlier, this solution would not require concrete, however its suitability for growth is strongly dependent on its location. Mangroves are more suitable for tropical or subtropical climates and prefer brackish or saline water. Besides aiding in coastal protection, mangrove forests can also serve as a carbon sink by absorbing carbon dioxide and helping with climate change mitigation.

There needs to be more attention placed upon the conservation of mangrove forests as the number of forests are currently being threatened by urban development and aquaculture, with one in six species of mangroves considered to be endangered. Through taking efficient measures for mangrove forest conservation, it can serve as a very efficient living seawall. Employing nature as a protective measure not only enhances environmental quality but does so without resorting to mining or additional material creation.

Lastly, another commonly known living sea wall are coral reefs. They serve as a barrier for coastline erosion prevention and wave energy reduction. A lot of pressure is exerted on coral reefs, due to rising temperatures, overfishing, and poor water quality. The number of coral reefs is declining in a way that is known as coral bleaching, in which they turn white due to increased environmental stressors. About 14% of the world’s coral reefs were lost between 2009 and 2018.

Despite the limited number of coral reefs, they are responsible for sheltering approximately 25% of the world’s marine life. In order to be recovered, corals must re-absorb the zooxanthellae, which can only happen after mitigating the active stressors. By taking more action on recovering coral reefs, they can serve as a suitable nature-based solution for coastline protection.

There are still numerous other possibilities of nature-based sea walls. This can include, but is not limited to, salt marshes, beach dunes, and seagrass beds. Coastal engineers have to focus on using more nature-based solutions like mangroves, living sea walls, and as they require less materials, is more economically viable, has a smaller environmental impact, can improve biodiversity, and be a huge terrestrial carbon sink.

Coral Reefs

Further Reading:
∣Exploring Nature-based Solution∣ Sustainable Buildings: Earthships
∣Exploring Nature-based Solution∣ Algae: A Solution to Plastic Pollution?

Reference:
Article 2 Sources:
https://www.worldatlas.com/articles/what-is-a-sea-wall.html
https://svc.com.au/living-seawalls-greening-manmade-seascape/ https://www.worldbank.org/en/news/feature/2021/07/26/mangrove-conservation-and-restoration-protecting-indonesia-climate-guardians
https://www.britannica.com/plant/mangrove
https://www.iucn.org/content/mangrove-forests-worldwide-decline
https://www.unep.org/news-and-stories/story/why-are-coral-reefs-dying
https://icriforum.org/about-coral-reefs/benefits-of-coral-reefs/