PM Network - May 2015

A Sinking
Feeling

Coastal cities around the world are sinking.

By 2100, sea levels are expected to rise by up to

1 meter ( 3. 3 feet), causing billions of dollars in annual damage. And extracting excess groundwater triggers a sinking effect known as subsidence.

“Land subsidence in many coastal cities is a major issue because it enhances flood risk,” says Gilles Erkens, PhD, senior geologist, Deltares Research Institute, Utrecht, the Netherlands.

In some cities, the ground is going down 10 times faster than the water is going up.

While the impact can be devastating, the right project can help city governments confront the problem head-on. “It’s difficult for a city to try to mitigate sea level rise because it’s a global problem,” Dr. Erkens says. “With land subsidence, the city itself is the cause, so it can try to mitigate it.”

Down, But Not Out

To stay above water, some
cities have launched mega-
projects spanning years—or
even decades. Jakarta, Indonesia—one of the world’s
fastest-growing cities and its fastest-sinking city—is
also the site of one of the world’s largest infrastruc-
ture programs.

Home to 28 million people, the Jakarta metropolitan region has sunk 13 feet ( 4 meters) due to subsidence during the past 35 years, according to Deltares. That’s why, in October 2014, Jakarta

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I MA G E CO UR TE SY OF WI TT EV EE N+ B

O S launched the first phase of a 40-year, US$40 billion risk management program.

The near-term measures include bolstering 32 kilometers ( 20 miles) of existing seawalls, while long-term solutions include the creation of drainage systems, pumping stations, an outer seawall and a chain of 17 artificial islands that will enclose Jakarta Bay. The enclosure will effectively create a large reservoir that can act as a storage pool for surging water.

“In this densely populated city, we proposed going offshore because that’s where you have the space,” says Victor Coenen, a project manager in Jakarta,