Coastal defense: New thinking needed

A major risk with the current obsession with climate change adaptation is in fact maladaptation: expensive solutions to problems that may never emerge or which themselves create new problems (the famous law of unintended consequences). This is evident in Vietnam where in 2009 the prime minister approved a plan to build concrete sea dikes (replacing the existing dirt dikes), at a cost of US$3 million per kilometer, along the entire coastline. This was motivated in part by a World Bank study that showed that most of the Mekong Delta will be flooded when sea level rises by 1 meter as it is predicted to do sometime between 2050 and 2100. A study by an academic at Can Tho University of the costs and benefits of concrete sea dikes around the Mekong Delta concluded that these were a good idea ( The assumptions on which the study is based are highly selective, however. For example, it assumes that rice and freshwater shrimp are the highest value land uses in the coastal zone, ignoring the benefits of saltwater aquaculture and changing market demands over time.

Cement sea dike at Ganh Hao, Bac Lieu Province

Meanwhile, in Europe and the USA, thinking has moved away from reliance on “hard” engineering solutions to coastal protection. The state of Maryland has started to buy up properties around the Chesapeake Bay to create a mosaic of land that will allow coastal wetlands to migrate inland as sea level rises. If residents want to stay in their homes, they can, but the state will provide no relief in case of flooding or collapse. Insurance companies have withdrawn coverage. In the Mississippi Delta, the state of Louisiana no longer provides power, water, school, and other public services south of I-10, the highway that runs east-west through New Orleans. When the Army Corps of Engineers, the cheer leaders of concrete-based solutions to water management, presented the budget for a new post-Katrina coastal defense system, the state turned it down. It couldn’t afford the US$100 million annual maintenance cost.

World-wide, governments love dikes and other large-scale engineering water management structures. They are visible, protect grateful voters (at least in the short term), and offer terrific opportunities for kickbacks and patronage. In the Mekong Delta, the German-funded WISDOM project has documented the mutually beneficial relationships between district departments of agriculture and rural development and dike construction companies ( But as the costs of these projects become apparent, questions are being asked. Even in the official media, doubts are being expressed about the value of the proposed US$2.4 billion (probably a huge underestimate) “super sea dike” connecting Vung Tau and Tien Giang, and the high dikes in the delta that were built to intensify rice production ( This kind of public scrutiny is particularly important in a country in which EIAs are “tick the box” exercises with no practical relevance.

Provincial governments along Vietnam’s 3,000-kilometer coastline find themselves in a particularly difficult position. On the one hand, they are criticized for any loss of life caused by storms. On the other, relocating people away from the coast is expensive and often strongly resisted. The last thing a provincial official wants to be associated with is a “social incident”. The provinces are also caught between Hanoi’s demand that a certain area be kept under rice production and the fact that conditions are getting saltier. So what solutions to coastal protection make economic, environmental, and political sense?

The first point to make is that sea level is rising but very slowly: by about 3.5 mm a year. This is not a crisis that requires an emergency response with potentially large negative consequences. The government has the time to consider the full costs and benefits of different options and take advantage of international experience. Second, the government needs to move away from a “defend at all costs” approach to coastal protection. The forces of nature are powerful and relentless. Adaptation that works with not against nature is the only realistic option, as countries much richer than Vietnam now realize. Third, the government needs to value mangroves not just for their storm protection functions but for the many other services they provide, particularly nurseries for marine life. The focus on storm protection is one reason why mangrove plantations are typically single-species and biologically poor. Management rules also need to change to give local communities the right to harvest mangrove resources sustainably; most mangroves are currently designated for strict protection. Finally, the government needs to shift thinking from a line of defense to a zone of defense. What would such an approach look like?

Most of the Mekong Delta is surrounded by compacted earth dikes. These are typically 2-3 meter high and erode rapidly wherever the mangroves have been lost. As sea level rises, it will become increasingly difficult to maintain them. Dike breaches and salt water flooding will become more frequent. Eventually, they will collapse completely. Behind the sea dike there are large areas of intensive shrimp ponds and seasonal rice-shrimp farms with no tree cover. A response to sea level rise is to transition this zone into a mangrove-based polyculture. The move to less intensive shrimp farming is already happening in some places because of the risks of disease and crop failure.

A mangrove-based polyculture has several advantages. First, because it relies on a more natural water flow, it is less susceptible to water-borne diseases. Second, shrimp grown under natural conditions are typically larger and fetch higher prices. There are also opportunities to have the shrimp certified as organic. These sell for a 10% price premium on international markets. Third, a polyculture produces crab and fish as well as shrimp, resulting in a more diverse livelihood. In the integrated shrimp-mangrove farms of Ca Mau, the net income from crab and fish is close to that from shrimp on a per hectare basis. Finally, because of its storm protection function, a polyculture removes the need to relocate people inland. Conversely, a concrete dike prevents mangroves from migrating inland as sea level rises and the consequent loss of mangroves will expose the dike to strong wave action. And if (or when) it fails, which is what happened in New Orleans in 2005, people living nearby can suffer devastating consequences.

The distance between the sea dike and the sea varies considerably. In Soc Trang, Bac Lieu, and most of Kien Giang, the distance is about 50 meters; in parts of Ben Tre and Tra Vinh, it is up to 2 kilometers because of the slightly higher topography. Households are not allowed to own land outside the dike; it is all state owned. But tens of thousands do, many of whom have lived there for years. Removing them is not an option. One option is for the government to offer resident households long-term leases and encourage them to invest in polyculture that protects them against storms and traps sediment at a rate that keeps pace with rising sea level.

A transition from existing land uses to a mature mangrove-based polyculture will take 20 years. This is the time-frame in which the government needs to respond. But this gradual approach to adaptation challenges a government fond of solutions (such as cement dikes) that can be implemented quickly in a blaze of positive publicity but which invariably turn out be much more expensive than planned. An incremental approach requires new thinking that takes into account the gradual pace of sea level rise, the risks of maladaptation, and the fact that the demand for agricultural products changes over time.

Not all the impacts from rising sea level rise are amendable to environmental-based adaption; in some cases, complete retreat or concrete-based defenses may be needed. In the Mekong Delta, however, a polyculture that yields multiple high-value products has the potential to increase the resilience of local communities and economies—and save the government a lot of money in the process.

Jake Brunner - Mekong Programme Coordinator (Viet Nam, Cambodia and Myanmar)

Work area: 
Climate Change
Marine and Coastal Ecosystems
Viet Nam
Viet Nam
Project and Initiatives: 
Building Coastal Resilience
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