Jakarta faces real, immediate threat of sinking

Berni K. Moestafa, The Jakarta Post, Jakarta

A major increase in construction, overexploitation of groundwater and unstable soil are causing parts of Jakarta to subside by up to eight centimeters a year, making the capital prone to more flooding, a surveyor company's report said.

A joint report by the city administration and state-owned surveyor firm PT Sucofindo predicted that from 1999 to 2005 Jakarta would sink at a rate of between 1.5 centimeters and eight centimeters a year.

During that period, North Jakarta may sink between two centimeters and eight centimeters, West Jakarta by 2.2 centimeters, East Jakarta by 1.5 to three centimeters, and South Jakarta by two centimeters.

"Lower land means there is an increased possibility that flooding will worsen," said the president of PT Sucofindo Appraisal Utama, Ganis Ramadhani, on Wednesday.

Sucofindo Appraisal is a subsidiary of Sucofindo. It conducted the study under the order of the city administration, which, according to one company official, wanted scientific proof that land was subsiding.

The study will help better anticipate flood problems and provide developers with data on the extent of land subsidence around the city.

Jakarta saw its worst floods in over 50 years last January. At least 30 people were killed and 15 more died from flood-related diseases, while thousands were forced to seek shelter for several weeks.

The city administration took the blame for failing to anticipate the magnitude of the flood, as well as developers for building houses in water catchment areas.

Parts of the city, however, have sunk by four centimeters to 91 centimeters over the past six years, according to one report by the City Mining Agency.

Ganis said land had subsided because of pressure on loose soil. The construction of houses and buildings have accelerated the sinking process.

Another contributing factor has been the exploitation of groundwater.

Water drawn from underground sources has loosened the soil, and along with the weight of construction, has caused land to subside until it becomes dense again, Ganis explained.

Groundwater accounts for 56 percent of the clean water Jakarta consumes, while rivers supply the rest through the city water company PAM Jaya.

Regulations on groundwater use exist, but only 7.5 percent of the water Jakarta draws from wells is regulated, said the head of the City Mining Agency, Muzahiem Mochtar.

He suggested that the city administration increase the tax rate for using groundwater to prevent people from wasting it.

But the exploitation of groundwater accounts for only 19 percent of land subsidence, he added.

Eighty percent is due to the weight of manmade structures, and one percent is because of natural processes.

While the impact was mainly from construction, Ganis said it also depended on whether engineers had factored in the risk of land subsidence.

Office buildings in Jakarta's business district on Jl. Jend. Sudirman and Jl. MH. Thamrin should be relatively safe, he said.

"It's usually tall office buildings and luxury homes that have anticipated the risk of land subsidence," said Agusman Effendi, the chairman of the Indonesian Real Estate Association (REI).

In that case, he explained, subsiding land would cause buildings to sink into the ground, but not collapse.

Agusman said developers should have had access to information on land subsidence prior to beginning their projects.

However, the city's 2010 master plan excluded geological factors.

Chairman of the Urban and Regional Development Institute, Wicaksono Sarosa, said he did not see any information related to land subsidence in the city's planning.

"The information should have been there (during city planning), but I guess it could be added later on," he said.

Wicaksono said developers should know the weight capacity of the land they plan to build on.

Ganis said Sucofindo's findings were incomplete and further measures would provide a more accurate picture of the extent of the problem.

"This is a preliminary study and we see opportunities for more (studies) in the future. They will be ongoing," he said.