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Built coastal flood defenses

To protect island coasts against rising sea levels and wave impact during storms and hurricanes, healthy coastal ecosystems such as mangroves, seagrass beds and coral reefs are crucial. However, especially in high risk zones, additional engineered structures may be necessary.

Such flood defence structures can be build on shores, in the sea, or they may be free floating. Many different forms of coastal flood defences exist, and the appropriate type of construction depends on the type and level of risk and the local environmental conditions. A few examples that may be relevant for the Caribbean islands of Curacao, Aruba and St. Martin are listed below.

Seawalls and Revetments

Seawalls are vertical or sloped structures built along coastlines to prevent erosion and protect infrastructure from wave action. Revetments are similar but typically sloped and made of rock, concrete, or other durable materials. Both work by absorbing and deflecting the energy of incoming waves, reducing their impact on the shore. These defences are especially useful in urban areas where critical infrastructure—such as roads, buildings, and utilities—needs protection from storm surges and rising sea levels.

More information: https://www.coastalwiki.org/wiki/Seawalls_and_revetments

Breakwaters

Breakwaters are offshore structures designed to reduce the intensity of wave action before it reaches the shore. They can be floating or fixed and are usually constructed from rock, concrete, or other heavy materials. By breaking the force of incoming waves, breakwaters create calmer waters behind them, which helps prevent coastal erosion and flooding. They are often used to protect harbors, beaches, and waterfront developments, and can also support marine ecosystems when designed with ecological considerations.

More information: https://nrcsolutions.org/living-breakwaters/

Storm Surge Barriers

Storm surge barriers are large, movable structures placed across estuaries, rivers, or harbor entrances to block the flow of water during extreme weather events. These barriers are typically closed during storms or hurricanes to prevent high tides and surges from flooding inland areas. They are particularly effective in densely populated coastal zones and areas with vital infrastructure. While costly and complex to build, storm surge barriers offer robust protection against catastrophic flooding and are a key component of long-term climate resilience strategies.

More info: https://www.ctc-n.org/technologies/storm-surge-barriers-and-closure-dams

Feasibility & Local Applicability

Environmental conditions such as wave energy, shoreline type, and sea level rise projections influence which defenses are most suitable. Engineering feasibility must consider foundation stability, material availability, and construction logistics, especially in remote or ecologically sensitive areas. Economic aspects include initial investment, long-term maintenance, and access to funding from international sources. Social and cultural factors including community engagement, tourism impact, and traditional coastal practices play a vital role in acceptance and sustainability. Ecological considerations are crucial, as hard infrastructure can disrupt marine habitats and may damage shorelines elsewhere. In any case, hybrid coastal defense plans that combine nature-based solutions with engineered structures are most effective. Finally, governance and policy alignment with national climate adaptation plans, zoning laws, and regional cooperation are essential for long-term success. A tailored approach that balances technical, environmental, and social dimensions is key to effective and resilient coastal protection.

Co-benefits

Coastal defenses can offer several co-benefits beyond flood protection. Engineered structures such as breakwaters can create calm zones that promote recreational activities and safe harbor conditions. Well-designed defenses may also boost tourism by preserving beaches and waterfronts. Additionally, these projects can generate local employment, strengthen community resilience, and contribute to climate adaptation goals.

Equity & Vulnerability Considerations

When implementing engineered coastal defense structures, it is important to assess how different communities, especially low-income, marginalized, or informal settlements, are exposed to flood risks and whether they benefit equally from infrastructure investments. Projects should avoid displacing vulnerable populations or limiting access to coastal resources.

Some coastal defense structures may protect the shore from erosion in one place, but may lead to increased erosion elsewhere. Such possible effects should be carefully evaluated.

Public participation, transparent decision-making, and equitable distribution of funding and maintenance are key. Additionally, designs must consider accessibility, cultural relevance, and long-term resilience to avoid deepening existing social and economic inequalities.

Costs

High | Engineered coastal defenses are costly. Costs depend on the location and size of the construction, the materials needed, design complexity and maintenance needs.

Case-studies & Examples

Literature

 

Adaptation Options Overview