Sea walls needed to stop floods: Experts

The Jakarta Post ,  Jakarta   |  Fri, 06/29/2007 10:24 AM  |  Jakarta

Anissa S. Febrina, The Jakarta Post, Jakarta

The threat of rising sea levels has prompted hydrologists to recommend Jakarta consider building more sea walls along its waterfront.

Higher than usual tides flooded parts of North Jakarta's Muara Angke district early last week, inundating houses and destroying the existing retention wall there.

""Climate change has prompted unpredictable cyclones that, when combined with regular tides, create surges of waves,"" Naval hydrologist Lt. Col. Rosyid said on the sidelines of a seminar Thursday.

""Like it or not, only higher sea walls combined with a proper drainage system could protect waterfront areas from such a threat.""

The State Ministry for the Environment has also warned that rising sea levels caused by global warming could put parts of the city underwater by 2050.

The ministry's report predicted world temperatures would rise by up to four degrees Celsius and sea levels would rise by between 18 cm and 58 cm by 2100.

A hydrologist from the Bandung Institute of Technology, Armi Susandi, earlier warned that the water level in Jakarta Bay was set to rise by 57 millimeters per year.

Most of the city's threatened low-lying areas are in North Jakarta, including Ancol, Cilincing, Koja, Pademangan and Penjaringan, Kelapa Gading and Tanjung Priok.

The Angke flooding, Rosyid explained, was caused by a combination of the spring tide during a new moon, an 18.5-year cycle when the moon was at its closest position to the earth, and the outside influence of a cyclone.

The high tide that inundated Angke homes measured 304 cm, the Navy's hydro-oceanology center reported.

Rosyid explained that sea walls would provide protection from tides, while a complementary drainage system consisting of pumps would channel water out of the protected area.

Residential areas in Muara Angke have been protected by a retention wall which has proved unable to withstand strong waves and high tides.

Four neighborhood units hit last week had only one pump each, which proved to not be enough to quickly remove the surging floodwater.

Residents are now planning to invite private companies to help provide more pumps for their neighborhood.

In contrast to the situation faced by Angke residents, flood protection measures have proved to be adequate for many private companies on the waterfront.

The sea wall and pump system suggested by Rosyid is in fact similar to a smaller scale system used at the Taman Impian Jaya Ancol recreation park in North Jakarta.

""We have build a retention zone standing between two and three meters in height above the existing ground to act as a barrier for the buildings behind it,"" said Sandy Rudiana, the head of Ancol's property planning department, Sandy Rudiana.

The zone was complemented with dozens of pumps that channel water into underground pipes leading to the sea, he added.

With the threat of rising sea levels, the company plans to continuously add to the height of its retention zone as well as increase the number of pumps.

Rosyid's proposed waterfront protection system, a simplified copy of the Netherlands' strategy to survive as a below-sea-level country, is one that would need significant investment.

Commercial areas like Ancol park can afford to set aside up to Rp 300 million for a large pump. But for people such as the residents of Muara Angke, such costs are beyond reach.

""Sooner or later, the administration will have to provide a proper protection system unless it wants to see parts of Jakarta underwater,"" Rosyid said.

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