Jakarta Floods Not Only Due to Damaged Peaks

This article was previously published in Kompas Daily on Friday, February 5, 2021. Because the flood disaster has hit Jakarta and its surroundings again, this investigative report is published again. The goal is for all parties to realize that this disaster needs serious handling.

JAKARTA, KOMPAS - Nearly all catchment areas of the Ciliwung River Basin have suffered damage from upstream to downstream. The Puncak area, located in Bogor Regency, West Java, which has long been considered a contributor to Jakarta's floodwaters, turns out to account for 8 percent of Jakarta's flooding. The remainder of Jakarta's flooding originates from issues in the middle to downstream zones of the river basin.

During the period of 2013-2018, based on the mapping of critical land conducted by the Watershed and Forest Management Agency (BPDAS-HL) Citarum Ciliwung, critical land in the water catchment area of the Ciliwung River has increasingly expanded and deteriorated.

In 2013, the critical land in the upstream watershed was recorded at 63 hectares, with moderately critical land covering approximately 7,400 hectares. Five years later, in 2018, the central part of the upstream zone located in the Puncak area, encompassing Megamendung and Cisarua sub-districts, had become severely critical, with an area of no less than 4,600 hectares, nearly half the size of the two sub-districts.

Similarly, in the central zone of the watershed, stretching from Katulampa Dam to Cijantung, East Jakarta, the condition has also deteriorated. Several locations in that zone were found to have started becoming somewhat critical in 2018.

According to IPB University hydrology expert, Hidayat Pawitan, it is not quite right to say that the Jakarta floods were caused by upstream problems in Puncak.

This is because the upstream zone of the Ciliwung River Basin (DAS) covers an area of 146 square kilometers or approximately 15,000 hectares. Meanwhile, the middle and downstream zones cover an area of 200 square kilometers or approximately 22,000 hectares. Almost all zones of the river basin have undergone land-use changes, which are now dominated by physical structures.

Areas that have transformed into urban regions, according to Hidayat, generally have a surface water runoff coefficient above 90 percent, meaning the soil's water absorption capacity is reduced to just 10 percent.

"From upstream to Katulampa, the area is 146 square kilometers. After Katulampa, there are still 200 square kilometers (middle and downstream zones) and that is more than half (of the upstream zone). So, what actually causes flooding (in Jakarta) is from Katulampa to downstream, the land use is all developed, all urbanized," he said in Jakarta, early December last year.

The land cover map along the watershed area of the Ciliwung River Basin from upstream to downstream, during the period of 1996-2016, shows rapid settlement growth in the middle and downstream zones of the basin. Settlements have also grown rapidly in the upstream zone but still leave areas of dryland agriculture, rice fields, plantations, and forests.

The study conducted by the Surakarta Research Center for Forestry Technology and Watershed Management (BPTKPDAS), Ministry of Environment and Forestry, shows that water runoff from the upstream zone contributes 8 percent to Jakarta's flooding, while the middle watershed zone contributes 9 percent.

The total contribution of Jakarta's floods from the Ciliwung River Basin and its surrounding areas is 24 percent. The rest of Jakarta's flood contributions come from the Kali Angke River Basin (19 percent), the Kali Krukut River Basin (13 percent), and the rest from inadequate drainage.

Head of BPDAS-HL Citarum Ciliwung Pina Ekalipta said that environmental damage in the Ciliwung watershed is already severe. As long as economic interests defeat ecology, the improvement of the Ciliwung watershed will always face obstacles.

To control flooding in Jakarta, the Sukamahi Dam is currently being built in Gadog, Bogor Regency. The dam has a capacity of 1.68 million cubic meters so it can reduce water shipments to Jakarta by up to 29 cubic meters per second.

Director General of Land and Spatial Control and Regulation, Ministry of Agrarian Affairs and Spatial Planning/BPN Budi Situmorang, who is part of the Bopunjur Project Management Officer (PMO), said that the Sukamahi Dam does not have a conservation function because it is more about controlling the water discharge from Puncak to Jakarta.

Chairman of the Indonesian Forest Care Foundation Transtoto Handadhari reminded that Jakarta and Puncak must be made into one watershed management. Because, the watershed is a unity of topography and ecosystem. Environmental improvement and repair must be simultaneous from upstream to downstream.