Jakarta, the nation’s capital and largest city, is sinking at a rate of 10 centimeters a year, a recent study has found.
The main causes for this phenomenon, which has been evidenced in recent years by several major floods, are extensive land extraction due to groundwater exploration and pressure from high-rise buildings, which is pushing parts of the city into the underlying water table.
“The land has been sinking for a long time, and the coastline is now encroaching on the heart of the city,” a geodynamics researcher from the Bandung Institute of Technology, Irwan Gumilar, told The Jakarta Post.
Irwan was a member of a research team led by Professor Hasanuddin Z Abidin that monitored Jakarta from 1997-2009.
“Few people may realize that the land is sinking by 10 to 12 centimeters a year,” Irwan said.
The highest rate of subsidence was recorded in coastal areas in North Jakarta, including Muara Kapuk and Ancol, where extensive development had increased pressure on the relatively young and porous soil beneath.
He said that apart from man-made factors, such as groundwater exploitation and aggressive development, the land in those areas was sinking because of natural factors, including soil compaction and tectonic setting.
Head of Disaster Mitigation Technology at the Technology Application and Assessment Agency (BPPT), Sutopo Purwo Nugroho, said the land subsidence could be seen in the city center, including at the BPPT building in Sarinah and on Jl. Sabang, both in Central Jakarta.
The Jakarta branch of the Indonesian Forum for the Environment conducted a study in 2008 on how land subsidence was affecting buildings in Central Jakarta. The study mentioned the Djakarta Theater in Sarinah, the former UN office (now the Elections Supervisory Body office) and the Jaya and BPPT buildings as among those affected.
Spokesperson for PT Sarinah M. Rusdy said the company was aware that land subsidence was causing the south wing of the building to incline.
“But the main building itself does not slope. [It can only be seen] on the extension built onto the south wing that was once used as an ATM center,” he told the Post. Rusdy said the company had renovated the wing and relocated the ATM center to the main building.
He said the building was still structurally sound, and that the company frequently hired consultants to audit the building’s condition.
Edi Santoso, manager of the Jaya building, which is now 40 years old, said the building’s management had not taken any action to deal with the problem.
“The engineer of the building apparently anticipated Jakarta would likely sink so he made the stairs to the building’s courtyard higher by 1 meter than the road level. However, that gap is now 50 centimeters,” he said.
Teddy Gumay, a tenant relations officer for the Djakarta Theater building said land subsidence had caused the south wing of the building to incline slightly.
“But that does not affect the main building,” he said, adding that the building was strong enough and was checked by experts every year.
“The stability of the building will not be affected much by the sinking land. At least it won’t cause the building to collapse unless a strong quake jolts Jakarta,” he said.