Reservoir ‘needs a closer look’
Adianto P. Simamora, The Jakarta Post, Jakarta

Geologists have praised a proposal to build an underground water reservoir to reduce flooding and water shortages in Jakarta, but warned of its potential environmental impacts.

They said that the administration needed to conduct extra studies of the geological composition of the area.

With a catchment area of 30 million cubic meters, the reservoir will be 17 kilometers long and 18 meters wide and situated 100 meters below the West Flood Canal running from Manggarai in South Jakarta to Muara Angke in West Jakarta.

“Based on our previous geological survey, the area is composed of unsolid sand, which could interrupt our drilling work and damage the surface area,” Lambok Hutasoit of the Bandung Institute of Technology told The Jakarta Post.

Lambok said that such a large underground reservoir should be built in a geologically stable area such as the southern part of the city bordering Depok.

“The area is composed of harder fragments of limestone and compact sand,” he said.

“It will be more affective to collect rainwater in these areas before it enters Jakarta to avoid floods. The quality of the water would make it a promising source for drinking water in the dry season.”

South Jakarta was originally designated a water catchment zone, but much of the land has been used for commercial activities.

The Rp 4.37 trillion reservoir was suggested by the city water regulatory body as part of the city’s integrated water management program.

Achmad Lanti, the body’s head, told Vice Governor Fauzi Bowo in a presentation that the reservoir would also contain household water waste and be a source of untreated water for the city.

A feasibility study will be conducted this year and the project is scheduled for completion in 2010. Robots controlled by global position technology will be used to conduct underground drilling work so as to avoid disturbing surface activities.

Chicago, Singapore, Malaysia and Hong Kong all have underground reservoirs.

Governor Sutiyoso is scheduled to present the plan to the House of Representatives on Monday.

M. Fakhrudin MT, a hydrologist from the Indonesian Institute of Sciences, said that placing the reservoir at a depth of 100 meters could worsen the quality of the city’s groundwater.

“The project could damage the underground layer that functions to remove pollutants from rainwater,” he said, adding that the cost of the project outweighed its benefits.

“Technically speaking, the underground reservoir could reduce flooding. But it needs further studies. The price of Rp 4.37 trillion is too expensive,” he was quoted by Antara as saying.

He said that the ongoing project to construct percolation pits throughout the city was a more effective way to avoid water problems.

“With the pits, all rainwater can go underground,” he said, adding that the pits cost only around Rp 250,000 each.

“If the administration set up two million pits, it would need only Rp 400 billion, or ten percent of (what the) proposed reservoir (would cost),” he said.

The administration and central government are currently encouraging the establishment of percolation pits in the city following the recent floods that inundated around 70 percent of Jakarta.

The administration has issued a decree requiring building owners to set up pits based on the roof widths, but few have been constructed due to poor law enforcement.

Of the average two billion cubic meters of rain that falls on Jakarta each year, only 170 million becomes groundwater.

sumber: http://www.thejakartapost.com/detailcity.asp?fileid=20070305.C01&irec=0