Street flooding in Jakarta in 2013.

Enlarge / Street flooding in Jakarta in 2013. (credit: Seika / Flickr)

Yesterday, Indonesian President Joko Widodo announced a plan to move the country’s capital from Jakarta to a new location in Borneo. The reason? Jakarta is bursting at the seams—and sinking.

Different sections of the city—home to 10 million people within an urban area of 30 million—are subsiding at different rates, but most fall in the range of 3 to 10 centimeters every year. Over the years, that has added up to as much as four meters of surface elevation change. This has wreaked havoc on building foundations and other infrastructure. And as Jakarta sits on the coast, where a number of small rivers meet the sea, the flooding hazard is also real. (The fact that sea level is rising doesn’t help.) That includes high-tide seawater flooding but also stormwater flooding as rain captured by the sprawling city’s pavement struggles to drain seaward.

Why the instability? Jakarta is a case of humans doing the wrong things in just the right place. River sediments deposited at the coast in places like this are naturally somewhat compressible. (It’s possible the bedrock beneath is moving a little bit and contributing, as well.) The actual weight of all the buildings and other construction at the surface is acting to compact the sediment a little, not unlike tamping down loose sand or soil in your yard. The biggest factor, though, is excessive groundwater pumping.

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