Bart Schultz
In a contribution to Flevolands Geheugen, I wrote about another polder in Jakarta, the Kelapa Gading Polder. This time one of the most famous of the 31 polders in Jakarta, the Pluit Polder.
For about five years, I was involved in a joint Master's programme of UNESCO-IHE in Delft and Sriwijaya University in Palembang, Indonesia. This eighteen-month programme for Indonesian students was conducted partly in the Netherlands and partly in Indonesia. Students were required to write their Master's thesis on a topic related to lowland development in Indonesia. Several theses focused on the polders in cities such as Jakarta, Surabaya, Semarang and Palembang.
All these polders are regularly affected by flooding. Furthermore, most polders are experiencing subsidence, often much faster than the sea level rise, which currently amounts to about three millimetres per year and could reach up to one centimetre per year. This subsidence is primarily caused by groundwater extraction for urban and industrial water supplies. In these cities, this subsidence often amounts to about ten centimetres per year, making the urban polders increasingly vulnerable.
The aforementioned problems certainly also exist in the Pluit Polder. One of our students wrote her master's thesis on water management and flood protection in this polder. The well-being of the Pluit Polder was also addressed in various Dutch-Indonesian workshops on lowland development, in which I have participated.
The surface level of the Pluit Polder is currently approximately between mean sea level and 2.5 metres below mean sea level. During spring tides, the water level in Jakarta Bay rises to approximately 60 centimetres above mean sea level. In 2008, 2009, 2010, 2013 and 2020, the polder was flooded due to breaches in the sea dikes during spring tides or due to extreme rainfall. It is therefore crucial that flood protection measures are properly maintained, raised and reinforced in a timely manner. Unfortunately, this is sometimes lacking.
The water management system in the Pluit Polder consists of open watercourses, a lake, a storage reservoir, inlet and outlet structures, and two pumping stations. Excess water from buildings and roads is temporarily stored in the Pluit Lake. From there, most of the water flows through a culvert with an outlet valve to the storage reservoir. Part of the water is pumped into the Muara Karang River alongside the polder. The water in the storage reservoir is pumped into Jakarta Bay. The storage reservoir has a surface area of 83 hectares, which represents 3% of the polder area. The total capacity of the Pluit Polder pumping stations is 53.3 cubic metres per second, which corresponds to a water layer over the polder of 20.8 centimetres per day.
Soil subsidence is therefore a significant problem for the Pluit Polder. With proper management and maintenance of the water management system, the existing water storage and pumping station capacity are sufficient. However, regular adjustments to the water management system and flood protection are crucial. This will require a continued joint effort and contribution from the government, businesses, and residents. Time will tell whether this will continue to be successful.
