Floods and Underground Reservoirs
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.
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.