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Sea dikes are sloped embankments built along the coast, usually covered with asphalt, concrete or vegetation. The slope absorbs energy from waves, while their cover prevents them from eroding. Sea dikes prevent seawater from flowing into the low-laying Mekong Delta, thereby protecting people, farmland, and infrastructure.
SEA DIKES
COASTAL SQUEEZE
MANGROVE FORESTS NATURALLY ADAPTING TO SEA LEVEL RISE
THE RISK OF COASTAL STRUCTURES
Sea dikes are widely used and can deliver short-term protection benefits. However, they also have negative effects. A fixed dike line can divide mangrove forests into isolated parts, starting a process called ‘’coastal squeeze’’. Behind the dike, mangroves remain in isolated areas or are replaced by aquaculture. In front of the dike, mangrove forests lose the ability to migrate inland. Over time, this results in weakening of the mangrove forest. When mangrove forests eventually completely disappear, erosion can cause risks for the dikes' stability. In the pictures below this process is illustrated.
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Due to the processes described above, dikes should be designed with great care. The initial construction costs represent only a fraction of the total life-cycle costs if erosion and structural damage increase over time. A healthy mangrove forest in front of a dike, can mitigate these costs, especially in extreme weather events. The Viet Nam Red Cross ↗ studied the difference in repair costs following two similar typhoons, comparing areas with and without mangroves in front of sea dikes in the Red River Delta. After mangroves were successfully restored, dike repair costs decreased from about 400,000 USD to 180,000 USD and shrimp-farm losses dropped from 5.7 million USD to 0.79 million USD. These findings highlight that designing dikes and mangroves to function as one integrated system can significantly reduce long-term costs.
COSTS
Sea dikes are essential, but they function within a complex and changing coast. Poorly designed structures that do not match local waves, sediment supply, subsidence and other conditions can create long-run risks and higher costs. The right path for long-term protection is site specific: in some areas, a higher dike may be needed, in other areas a mangrove forest and often a good combination of both.
Short-term interventions are sometimes necessary, but their long-term impacts are hard to predict. Therefore, monitoring of waves, water levels, shoreline position, subsidence and mangrove conditions around sea dikes is essential. These efforts help ensure that coastal protection remains both resilient and economically sustainable.
LONG-TERM VISION
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