Jakarta is built in a lowland area that was once a sea and was formed by the sedimentation of soil collected from the mountains around the Bandung Basin up to Bogor during the Holocene and Pliocene ages.
By
JOSAPHAT TETUKO SRI SUMANTYO
·5 minutes read
Until now, sedimentation in the western and eastern parts of Jakarta Bay continues to occur. The distance the coastline protrudes into the sea will increase, and someday Jakarta Bay will become land. The main deposits that have formed this land, according to a Geological Research Center map, are alluvium, floodplain sediments, coastal ridge sediments and Banten tuffs, meaning floods have played an important role in the formation of this region since long ago. Therefore, the "annual nature party" in the form of floods provides a gift in the form of the land we call Jakarta today.
Old maps from the 1800s belonging to the writer\'s personal collection show that the northern parts of Jakarta were still swamps. Some parts of Jakarta that carry the name "Pulo" reportedly used to be islands and later became part of the mainland due to sedimentation. The physical characteristics of swampy land means it naturally has poor absorption, meaning that flooding has been an annual event since the founding of the city as Jayakarta in the Sunda Kepala region when Fatahillah of the Sultanate of Cirebon succeeded in driving the Portuguese army out of the area on June 22, 1527.
This port was located in Penjaringan village, Penjaringan district, North Jakarta. Although the name of the area has changed from Jayakarta (1527-1619) to Batavia/Batauia, Jaccatra (1619-1942), Djakarta (1942-1972) and Jakarta (1972-present), floods still occur every year.
The conventional way is no longer adequate
In 1611, Vereenigde Oostindische Compagnie (VOC) obtained permission to open a trading office in Jayakarta and expanded the office next to the estuary east of the Ciliwung River into an office complex, with warehouses and Dutch residences, where Jan Pieterszoon Coen was the governor general (1618-1623). Coen avoided annual flooding by building a high stone wall. Coen also built a number of canals and tunnels on the Ciliwung River to avoid flooding in his area. The West Flood Canal (Manggarai Flood Gate up to Muara Angke) was built by Governor General Johan Paul van Limburg Stirum in 1920 after a great flood in 1918.
After independence, the Indonesian government began to concentrate on the problem of flooding in 1965. Governor Ali Sadikin built reservoirs and new canals, namely the Cengkareng and Cakung channels. However, another major flood occurred in 1976. The next major floods occurred in 2002 and 2007 under the leadership of Sutiyoso (1997-2007). During Governor Joko Widodo\'s era river normalization started to be carried out and the function of the city’s reservoirs was improved. During the administration of Basuki Tjahaja Purnama there was a major flood in 2015. Five years later, in the Anies Baswedan era, in early 2020 there was another big flood in Jakarta.
This five-year cycle of major flooding requires intelligent thinking to solve. After each major flood, the city has a five-year window to prepare for the next flood. The natural absorption of the soil cannot be relied upon. According to a map of the earth\'s surface published by the Geospatial Information Agency (BIG), nearly 80 percent of Jakarta is covered with concrete, asphalt and swampland. In the rainy season, the soil is quickly saturated, resulting in flooding.
If this excess water can be contained, then flooding can be avoided.
If we look closer at the annual data, we can see that the areas inundated with 1 to 3 meters of water are always the same, becoming temporary reservoirs. If this excess water can be contained, then flooding can be avoided.
At present, the local government’s management of waste water channels is inadequate. Bad drainage can result in clogging during the floods. Flood and sewage water mixes so that all members of the community, regardless of their economic level, bear the risk. It is time for the regional government to start managing underground wastewater and industrial waste treatment. When using optical satellite imagery, Jakarta Bay looks like a giant septic tank.
Survival reservoirs
Other capital cities in the world have their own methods for dealing with flooding according to the characteristics of their regions. Jakarta, which is basically marshland, has a very poor natural absorption capacity during the rainy season. This is made worse by the limited surface area.
So far, each governor has constructed canals to normalize or naturalize the width and flow of major rivers through the capital city so the water can flow out to sea. This has been unable to drastically reduce flooding in the capital city. Therefore, a fast absorbing system needs to be made in accordance with the increase in rainwater during extreme rainy seasons by building a survival reservoirs.
The conventional reservoirs that already exist in Jakarta do not have a significant effect on flood-affected locations because they are located far from these areas. The high cost of land acquisition for building dams in the city is also a particular obstacle. Therefore, we can make underground reservoirs just below the locations affected by flooding. This process can utilize the same technology used to make the MRT.
Underground reservoirs can be used to absorb water quickly so that the surface is protected from floods. The collected water can also be used as a source of drinking water and by the park service in the dry season to water nature strips, and even someday for agriculture in the city, nurseries and other uses.
The government is currently concentrated on the management of underground facilities. The BIG has also started mapping underground utilities to prevent future accidents. The management of industrial and residential waste is also a necessity to avoid property damage and health risks from flooding. Underground reservoirs can be used in other cities affected by floods and land subsistence, such as Semarang, Surabaya and Bandung. Flood waters can be a blessing water if we manage them with a touch of Indonesian thought and technology.
Josaphat Tetuko Sri Sumantyo,Professor and Head of the Remote Sensing Department, Chiba University, Japan; Member of the Board of Experts of Habibie Program Alumni Association (IABIE)