Indonesia’s capital, Jakarta, is sinking into the sea. And forget the fuss about Venice dropping at a rate of 0.08 inches per year, Jakarta – home to 10 million people and counting – is sinking at between 2.9 and 6.7 inches per year, as some areas submerge faster than others. While rising sea levels are a contributing factor to this, by far the greater cause is unchecked groundwater extraction from below the city to provide fresh water to the ever-growing population. To try to stave off the impending inundation of sea water, the city has engaged Dutch firm Witteveen+Bos to manage a $40 billion land reclamation and sea wall project that will construct 17 new islands and take an estimated 30 years to complete. But will it be enough?

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About 40 percent of Jakarta already lies below sea level. The extraction of groundwater reserves for the water supply has left large caverns under the city, which are collapsing. Since record keeping began in 1974, some parts of the city have sunk as much as 13.5 feet and Dutch hydrologist JanJaap Brinkman noted in 2012 that a further drop of between 16 and 20 feet could be expected by 2100. The city was ravaged by flooding in 2007, 300,000 people were made homeless by flooding in February 2014, and an estimated one million people are at risk if the current sea wall is breached. Last year, the sea level was only 3.9 inches below the top of the wall. Not only would sea water inundation physically threaten lives and property, it would contaminate the underground freshwater supply on which the city depends.

Related: Rising Sea Levels Could Cause Two Times More Groundwater Flooding in Coastal Areas Than Previously Predicted

While ideally, the rapid construction of a complete enclosure dam between the eastern and western ends of Jakarta Bay would keep the sea back, it’s logistically unfeasible. It turns out, for instance, that supplying enough soil for such a wall would require more dredging vessels than are currently available in the entire world. In 2012, Jakarta called for tenders to develop a master plan to save the city, and a consortium led by Witteveen+Bos won the contract. On 9 October, 2014, the first pile was sunk for a new seawall, marking the start of work on the National Capital Integrated Coastal Development (NCICD) project. The master plan involves offshore flood protection measures in Jakarta Bay, as that is the only area of the city that still offers enough room for such activity.

Temporary protection measures will be put in place before a new enclosure dam is built in the bay. This reservoir will borrow from lessons learned by the Dutch in creating a buffer zone for water flows and influx from the 13 rivers that feed into the bay. A huge part of the estimated $40 billion cost of the project is the massive investment in one of the world’s largest hydraulic engineering undertakings. The accelerated construction of urban sewer systems and water treatment plants is also a key aspect of the plan. This infrastructure is required as a matter of urgency to prevent a ‘black lagoon’ of sewage forming on the city side of the new seawall. In total, 17 islands accommodating a combined 900,000 residents and day workers will be built in the bay and the plans include a new waterfront shaped like the mythical Garuda bird, the national symbol of Indonesia. It now remains to be seen whether the project can survive the changing landscape of Indonesian politics, and the project has been designed in three phases to try to mitigate this risk.

+ Witteveen+Bos

Via Gizmodo

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