Nature-based solutions can reduce coastal protection costs

The world’s coasts are at risk – but not everyone is in the same position

All coasts face erosion risks from storms and natural disasters. But Southeast Asia, one of the regions that is most sensitive and vulnerable to climate change, is at particular risk. And with its broad and densely populated coastlines, the impacts of erosion can be severe.

While the region has several seawalls and dikes that have protected its coastline against flooding, wave attacks, typhoons, and eroded foreshores have made coastal defences susceptible to breaches. And in a literature review covering the region, academics found an even more extreme case.

A groin constructed at the river mouth of the Ca Ty River estuary interrupted the flow of sediment along the coast. This has led to downdrift erosion on the southern beach of Duc Long Ward and took away the buffer that the beach provides against wave attack and storm surges. This caused the collapse of hundreds of houses, requiring residents in the Tien Duc Area to relocate.

What can be done to prevent these kinds of disasters and secure those regions against flooding, coastal erosion, and severe waves? While there are advanced coastal defences available, the high-tech coastal protections seen in the US and EU may be difficult to justify economically for some parts of the region, particularly for less densely populated areas. 

And as I mentioned in my previous blog about river flood defences, when grey infrastructure is implemented without the necessary budgets and engineering expertise, structures can be built on weak foundations that risk failing prematurely.

Using nature to secure the coast at a lower cost

For areas with limited construction budgets, combining nature-based solutions (NbS) with traditional grey infrastructure can help protect coastlines, while delivering other benefits to local ecosystems. This hybrid approach can reduce the required crest levels for grey coastal protections and extend the design life of existing structures. And because NbS can naturally adapt to climate change impacts, it reduces the maintenance requirements and costs of grey solutions. In this way, NbS complement and augment traditional grey infrastructure, rather than fully replacing it.

And there are NbS that can aid in mitigating erosion, stabilising foreshores, and attenuating waves to minimise some of the worst impacts of storm disasters.

For example, some countries with warmer climates and muddy coasts are turning to mangroves. Or in case of tropical areas with clear water, coral reefs can be part of their coastal protection system. In a sandier environment, beach nourishment programmes can help build out and enrich shorelines. All these measures are solutions in the foreshore of the coastal protection system, and act as natural buffers to rising sea levels and storm surges. They can protect coastlines while contributing to biodiversity and improving water quality. If needed, these solutions can also be complemented with measures that trap sediment and stabilise soil to create the right conditions for the targeted ecosystem. Once established, these living foreshores can adapt to changing climates and offer significant natural protection against storm erosion while supporting a diverse range of marine life.

Even in countries that have the resources to build and maintain complex grey coastal protections, NbS like salt marsh restoration in more temperate climates can support seawalls and dikes while offering co-benefits to local ecosystems.

So, if these techniques can protect coastlines and support biodiversity at a lower cost than traditional coastal protections, why isn’t every region implementing them?

The barriers to nature-based coastal protection

The barriers to successfully implementing NbS are often site-specific and based on the geographical conditions. For instance, dune systems are not suitable for Singapore due to the lack of natural dune climates necessary for sand replenishment, and mangroves can only flourish on coasts that are tropical and at least a bit muddy. Implementing NbS without considering such conditions can lead to failure. 

Outside of these kinds of geographical limitations, there are four main barriers that prevent public bodies from embracing the benefits of NbS for coastal protection.

Coastal NbS references around the world

Outside of academia, nature-based coastal protections are also proven at scale in reference projects. 

In the Netherlands, Royal HaskoningDHV worked with Rijkswaterstaat (the executive agency of the Dutch Ministry of Infrastructure and Water Management) to reinforce the Houtrib dike. To improve the natural value of the area, the dike was reinforced with sand, and mud released during sand extraction was used to construct a nature reserve that supports mussels, snails, insects and fish. The sand extraction pit also functions as a mud trap, improving water quality across the lake.

And we’ve supported the municipality of Beira, Mozambique, engaging stakeholders and designing solutions to protect the region’s vulnerable coastline from erosion. As much of Beira’s coastline is muddy and/or sandy, we were able to design solutions incorporating mangrove belts and revegetation of dune ridges. Our designs offer flexible and hybrid solutions to protect the half a million residents of Praia Nova from frequent flooding, while delivering biodiversity and sustainability co-benefits, at the lowest possible cost.

Learn more about nature-based solutions for coastal protection

Overcoming the legal and spatial barriers to NbS can help protect vulnerable coastlines from increasing flood risks, but it demands careful planning, collaboration across stakeholders, and engineers that are willing to consider all options and opportunities. Crucially, it also requires a change in how public and private organisations view NbS. 

Whether they’re augmenting grey solutions or a first step towards reducing impacts of waves, the positive impacts of NbS on coastal protection and local communities are clear. The sooner public bodies and financiers understand this, the better we can protect the world’s vulnerable coasts.