Nature-based solutions improve coastal defenses

The relentless march of climate change poses an unprecedented challenge to coastal defenses worldwide. Traditional “hard” measures like concrete sea walls, while historically favored for their protective capabilities, are increasingly under scrutiny for their environmental impact and sustainability. 

A recent study led by the University of Tokyo suggests that integrating nature-based solutions with conventional coastal defense strategies could provide a more adaptable and sustainable approach to managing coastal risks.

Traditional coastal defenses can’t keep pace 

“Sea walls, dikes, dams and breakwaters, the so-called traditional hard measures, despite being the most popular coastal defenses globally and with proven track records, are facing challenges to keep pace with increasing climate risks,” explained lead author Lam Thi Mai Huynh, a doctoral student in sustainability science at the University of Tokyo. 

“These hard structures are expensive to build and require continuous upgrades and repairs as sea level rises and climatic hazards become stronger. Although they are good at mitigating certain coastal disaster risks, they can also cause significant disruption to coastal communities and have adverse environmental effects.” 

“Furthermore, they often significantly alter the seascape and sometimes alienate local communities from nature and the very environment we seek to protect.”

Assessing the efficacy of various coastal defenses

In their study, the researchers assessed the efficacy of various coastal defenses by reviewing 304 academic articles. They categorized the defenses into four types: natural environments, soft measures that enhance natural elements, hard measures like concrete barriers, and hybrid solutions that combine elements of the first three categories. 

Soft and hybrid approaches were found to be more cost-effective than purely hard solutions, with hybrids offering the greatest hazard reduction in low-risk settings. 

Despite the lack of data on their performance during high-risk, extreme weather events, these findings advocate for the strategic incorporation of natural elements into coastal defense plans.

Protecting coastlines and their natural beauty

Japan’s struggle to protect its coastlines while preserving natural beauty illustrates the complexity of this challenge. 

Once renowned for its untouched coastal landscapes, nearly 40% of Japan’s coastline had been modified by the early 1990s, trading natural vistas for concrete fortifications in response to the threats of tsunamis, typhoon swells, and rising sea levels.

The potential of hybrid coastal defenses 

This study underscores the potential of hybrid coastal defenses, which utilize both hard and nature-based solutions, to offer effective risk reduction while preserving environmental integrity. “Our results indicate that among all coastal defense options in lower-risk areas, hybrid measures provide the highest risk reduction. 

Hybrid measures can harness the advantages of both hard and soft measures. They provide the immediacy of an engineered barrier while largely maintaining the ecological functionality of a permeable vegetated zone,” Huynh explained.

Further research is needed 

Senior author Alexandros Gasparatos from the Institute for Future Initiatives at the University of Tokyo emphasized the innovative nature of such strategies, though he cautioned that they are not a panacea for all coastal challenges. 

The team highlighted the importance of further research, particularly experiments in high-risk situations, to better understand the comparative effectiveness of different coastal defense strategies during extreme events.

Cautious expansion of nature-based solutions

Despite these uncertainties, the researchers advocate for the cautious expansion of nature-based solutions in coastal defense strategies, especially in areas of lower risk. Such approaches not only mitigate climate change impacts and store carbon but also reconnect communities with their natural surroundings and promote biodiversity.

“I firmly believe that we must think more carefully about the design and function of these barriers in this era of ever-accelerating climate change. Not only can nature-based solutions contribute to risk reduction and climate mitigation in many areas, but they can also help reconnect people with nature and support biodiversity,” said Huynh.

“Greening our coastlines can create spaces which enhance quality of life, foster community well-being and inspire environmental stewardship.”

Natural coastal defenses

The best natural coastal defenses offer protection against coastal erosion, flooding, and storm damage. They enhance the resilience of coastlines while supporting biodiversity and local communities. Here are some of the most effective natural coastal defenses:

Mangroves

Mangrove forests are highly effective at reducing wave energy, trapping sediments, and stabilizing shorelines. They can absorb more wave energy than constructed seawalls and reduce the height of waves passing through them.

Coral reefs

Acting as natural breakwaters, coral reefs can dissipate up to 97% of wave energy before it reaches the shore. This reduces erosion and protects coastal habitats and communities from storm surges and sea-level rise.

Salt marshes

These coastal wetlands are effective at absorbing wave energy and trapping sediments, which helps to stabilize shorelines and reduce coastal flooding. Salt marshes also provide habitat for a variety of wildlife.

Seagrass beds

Seagrasses stabilize the seabed, reduce wave energy, and prevent erosion. They also contribute to carbon sequestration and support marine biodiversity.

Sand dunes

Dunes act as barriers against storm surges and high waves, protecting inland areas from flooding and erosion. Vegetation on dunes can stabilize them and help in their recovery after storms.

Oyster reefs

Similar to coral reefs, oyster reefs can buffer shorelines against wave action, stabilize sediments, and reduce erosion. They also improve water quality by filtering out pollutants.

The study is published in the journal Nature Communications.

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