Build dykes to protect against rising sea levels: experts

By Hasnita A Majid
Channel NewsAsia
09 May 2007

SINGAPORE: Experts say Singapore can build a system to protect itself from rising sea levels due to global warming - they recommend dykes, or a sea defence system.

As an island Singapore can be affected by rising sea levels as a result of melting ice caps because of global warming.

So the country is looking into the possibility of building dykes to tackle this problem, as disclosed by Minister Mentor Lee Kuan Yew at a recent dialogue.

Singapore is tapping the experience of the Dutch, who have been using dykes for many years.

Dykes are used to protect cities in the Netherlands, half of which were built below sea level.

Dykes have also been used in countries such as the US and Japan.

But there are different conditions for different countries.

"It depends, a little bit on the elevation of the land in Singapore. I think it makes sense to do a good study on this, to verify where land is prone to future inundation. Of course in Singapore you have a little handicap of finding fill materials.

"Locally, conditions can be also difficult to integrate into the coastal developments, so you have little space and of course, locally the water depth is quite significant. So you have to take that into account," says Tjitte A Nauta, Project Manager, Marine & Coastal Management, Delft Hydraulics.

"Altogether, I think it makes sense to study… the impact of inundation on the area and then come up with a plan on how to protect it… and then you go into these designs, whether you consider dykes or consider sea walls or whatever…

"Basically you can do it anywhere where land can be inundated. And that depends on where you are worldwide, and in some cases it's basically affected by tides.

"And some areas are affected by tides that come in, but it is to protect the land behind it.

"Then you make a decision once you know what the local conditions are and when you should go for the dyke; when you should go for the sea wall; and when you should go for breakwaters to take care of the water exposure … or you go for a combinations of all these," continues Nauta.

There are also varying safety standards. In the Netherlands for example, it has a very strict standard which allows a potential of only one accident per 10,000 years, while in other countries like the US, it is more lax, allowing the potential of one accident in a 100 years.

Delft Hydraulics says that in the Netherlands, dykes are also used to create land from marshland and other water bodies, by constructing the structures to block off the areas and pumping them dry - hence creating what is called a polder.

This model, it is believed, can also be applied to Singapore to create more land.

Nauta explains how it works, "The polder system is basically an alternative to traditional land reclamation. With land reclamation I mean filling up the area until it’s above the running water level. But a polder works in a slightly different way.

"Basically, it starts by building a dyke in the water system and then pumping it dry - the land within the dyke is pumped dry so that a land is created on the existing bed of the sea or the lake or whatever.

"In your case it would be the sea environment so the polder [has] to be built in a different way than the polders that have been built in the Netherlands… but in the Netherlands we have created a substantial increase of our land… by just building large polder schemes…

"…and they are in a sense a cheaper alternative to land reclamation because you don't need all the fill materials."

But having to pump the water out also means more energy required, which may result in higher costs.

Still, the long term gain would be significant because dykes not only serve as a water defence system but can double up as an area to maintain biodiversity.

And this is exactly the objective of the Singapore Delft Water Alliance which is based at the National University of Singapore, NUS.

"We are involved in a number of research programmes - building with nature, understanding how we can enhance traditional engineering…

"…by enhancing the performance of a system, by increasing biodiversity in order to arrive at a better system, to develop better protection.

"The modern eco-hydraulics is that we can enhance the performance of sea defence and enhance the biodiversity at the same time.

"In the Netherlands for example, there's a programme called "Rich Dykes". So they are not simple structures made of concrete but structures that involve working with nature," says Associate professor Vladan Babovic, Director, Singapore Delft Water Alliance.

The NUS is also drawing up plans for a system that performs multiple functions.

It is setting up Aquatic Science Centres in canals and coastal areas to study the viability of an ecosystem where the water can be kept clean at the same time. - CNA/yy