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19 January 2009

Floods in Jakarta

West Java is known as the land of two seasons, the rainy season which lasts from November to May and the dry season which lasts from June to October. The administrative area, which is named DKI Jakarta, is now 662 km2 has ten rivers running through it is located on delta comprising three main rivers, the Ciliwung, the Pasanggrahan and the Sunter rivers which annually flood during the monsoon period.
Until the middle of the last century, the Ciliwung river, which is 128 km long, has a 385 km2 basin area and about 75% is outside Jakarta, was the main cause of floods in Jakarta. All flood control works constructed before then were aimed to cope with floods from that river. When a vast tea plantation estate was opened in the upstream part of the Ciliwung river basin, large-scale work was implemented in 1924. A floodway was constructed to divert nearly 300 m3/sec floods westward, out of the city area. Later on the original river channel was reduced in size and connected to some drainage channels which help to carry some of the remaining flood burden into the sea.
The region regularly experiences severe floods such as in 1996,2002 and 2007. The problem of floods in Jakarta came to the forefront after two consecutive severe floods in 1996 , 2002 and 2007. The damage was colossal when floods of severe magnitude. In January 2002 and 2007, the flood inundated 60% of the land area last for about six days and affected thousands of people, and an estimated damage of billions of rupiah. In 1996, the flood was less severe; nevertheless the flood-affected area was about 30% of the land area.
Interception of flood flows from all rivers before entering lowland areas (i.e. the proper city area at the time) was planed by two floodways. The Western Floodway was meant to be an extension of a floodway constructed in 1924 which intercepts the Ciliwung, Cideng and Krukut rivers. The extension was intended to cope with the Grogol, Sekretaris and Angke rivers as well. The Eastern Floodway was aimed to intercept all other remaining rivers (Cipinang, Sunter, Buaran, Jatikramat and Cakung). The floodways were planned to contain 100-year floods, i.e. 290–525 m3/sec for the Western Floodway and 101–340 m3/sec for the Eastern Floodway.

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