Jakarta Strives to Achieve Flood Control Target

KOMPAS/PRIYOMBODO

Aerial photo of the Brigif dam construction project in the Jagakarsa area, South Jakarta, Wednesday (2/11/2022). This dam is expected to be able to withstand the overflow of water from the Salak river which flows from Depok and Tanah Baru.

JAKARTA, KOMPAS — Jakarta has so far been striving hard to intensify the development of flood control infrastructure. In the Jakarta flood control scheme drawn up by the Jakarta Water Resources Office, the rate of water discharge into the capital city reaches 3,389 cubic meters per second.

The capacity of the existing flood control infrastructure of Jakarta is now only 1,141 cbm per second. This capacity of the existing infrastructure is part of the design of the flood control infrastructure under construction and targeted to manage 2,357 cbm per second.

“There’s still a difference of 1,032 cbm per second [from the target of infrastructure development in the total of water inflow] that has to be contained. It is planned to be collected by means of reservoirs or basins. Their precise locations are being studied,” said head of the flood control and drainage planning division, Jakarta Water Resources Office, Maman Supratman, on Friday (3/2/2023).

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With reference to the Jakarta flood control scheme, the upstream area as far as Manggarai optimally serves as a water parking location. There are also the East Flood Canal and West Flood Canal in the basin area as well as polders (water retention pools) around the downstream area.

This overall control from upstream to downstream is suited to the geographic condition of Jakarta. Based on the provincial ecoregion map of the Jakarta Environment Office of 2014, the capital is divided into a marine plain, which is a muddy tidal area (vulnerable to flooding), a beach ridge, and a lowland between beaches (vulnerable to inundation).

There is also a fluvial plain comprising marshy land (prone to inundation and flooding) and fluvio-marine land (prone to inundation, tidal overflow and flooding) in Jakarta’s middle part northward. Lastly, there is a volcanic plain and an undulating sloping plain from the center southward.

Canals have failed due to the topography level of Jakarta so the water cannot flow. Sedimentation and heaping waste block the flow of water.

Restu Gunawan in his book Gagalnya Sistem Kanal Pengendalian Banjir Jakarta dari Masa ke Masa (The Failure of Jakarta’s Flood Control Canal System Over Time, 2010), mentions the micro and macro systems as the key to flood control for almost a century. In the macro system, the building of canals, polders and water collection reservoirs is chosen.

Nevertheless, canals have failed due to the topography level of Jakarta so the water cannot flow. Sedimentation and heaping waste block the flow of water.

The canal system can only reduce the burden of flooding momentarily. When rainfall is high and more frequent, the water holding capacity is exceeded, giving rise to greater threat and bigger losses. The polder system is also problematic. The areas already designated as polders are crowded with settlements.

KOMPAS/PRIYOMBODO

An excavator dredges sedimentation mud in the Melati Reservoir, Tanah Abang, Central Jakarta, Wednesday (21/12/2022). The DKI Jakarta government is dredging rivers and reservoirs as a measure to anticipate flooding during the rainy season.

Water parking

Realizing the weakness of canals and the problem faced by polders, Jakarta implemented its 942 program, covering the development of 9 polders and 4 reservoirs and the revitalization of 2 rivers. This flood control project has been underway since November 2021 with its target of completion set in March 2023.

The nine polders are built in Kelapa Gading, Pulomas, Muara Angke, Teluk Gong, Mangga Dua, Green Garden, Marunda, Kamal and Tipala-Adhyaksa. The reservoir development is undertaken in Pondok Ranggon, Brigif, Lebak Bulus and Wirajasa or Pilar Jati, while revitalization involves Besar River’s Museum Bahari canal diversion and the building of diversion infrastructure of downstream Ciliwung River-Pasar Baru.

“Reservoirs are designed to reduce floods from upstream. Every [reservoir] point has its own flood reduction capacity,” said Maman.

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An example is the Brigif Reservoir for water parking from the Krukut River. When rainfall is 250 millimeters per day, flood reduction is designed at 15.3 percent. This estimate is based on the discharge rate and water flow calculations. For instance, at the discharge rate of 1,000 cbm, the parking water is around 153 cbm. The remainder flows into Kemang, Bendungan Hilir and the West Flood Canal.

With this fact, in spite of the additional reservoirs, floods cannot yet be drastically reduced. Moreover, the condition of drainage in Jakarta remains at the capacity of the daily average rainfall of 100 mm. Unsurprisingly, big floods occurred in Jakarta when extreme rainfall reached 377 mm in 2020 and 260 mm in 2021.

Holistic

In order to halt the race between infrastructure and water excess, Jakarta is developing a roadmap for flood control in a holistic way. Now the entire infrastructure is being evaluated to obtain data on its necessity or capacity and cost estimation. “There should be balance, integration between rivers and water parking,” said Maman.

Restu Gunawan described flood control in Jakarta as improving as time went by. “[Yet] it has mostly been focused on Ciliwung. In fact, Jakarta is traversed by 13 rivers and now the coverage of floods is expanding in Greater Jakarta. This should be properly handled,” he added. (Z08)

This article was translated by Aris Prawira.