Title: recent situation of land subsidence and countermeasures in jakarta
Abstract: As the capital city of Indonesia, Jakarta has a population of about 10,171,000 people (government statistics of Indonesia in 2015) and is rapidly developing as an economic and political center. Meanwhile, with over-abstraction of the groundwater as one cause, land subsidence of more than 2 m has occurred in the northern part of the capital Jakarta since 2000. This is considered to be mainly due to over-abstraction of the groundwater at factories or buildings, accompanied by recent economic growth and population concentration in the capital. Especially, the tendency is remarkable in lowlands in the northern part where economic activity concentrates, and in some areas damage such as sea water flooding at high tide is becoming obvious. Based on 1925, the land subsidence rate in 2015 is 3 to 4 m, and the land subsidence of 5 cm or more per year has occurred. It is subsiding at a rate rarely seen in the world. Land subsidence is occurring in a wide range including the center of Jakarta, resulting in enhancing flood risks such as floods and storm surges, increasing flood damage, bringing inhibition of civic life such as stagnation of logistics. The impact on the economy is great. Countermeasures against land subsidence will require not only monitoring, but also many measures such as restriction of groundwater abstraction, developing alternative water sources, promoting adaptation measures. In order to establish a system in which related government organizations cooperatively promote these countermeasures under one action plan, the followings are needed; 1. To propose effective mitigation measures to stop land subsidence and to conduct rough cost estimation of the measures, 2. To investigate risks of land subsidence and to estimate the costs of adaptation measures, 3. To raise awareness about countermeasures against land subsidence among stakeholders, and 4. To promote the activities for implementing countermeasures. Under these circumstances, the Government of the Republic of Indonesia (hereinafter referred to as “GOI”) requested Japanese Technical Cooperation, and Japan International Cooperation Agency (hereinafter referred to as “JICA”) commenced the technical cooperation project named “the Project for Promoting Countermeasures against Land Subsidence in Jakarta” in May, 2018. In the Project, InSAR (Interferometric Synthetic Aperture Radar) analysis was conducted to monitor the land subsidence in the recent years. For the analysis, L-band InSAR data obtained by the satellite named ALOS (2007-2010) and ALOS-2 (2014-2018) was used. Land subsidence is still continuing in particular areas and even 10 cm/year level of subsidence was found from the analysis of recent years. In 2007 - 2010, markedly subsiding part was seen in the northern and the northwest part. On the other hand, in the second half of the analysis period, or 2014-2018, there is a tendency for the subsidence in the northern part to calm down, but the northwestern part shows a constant subsidence tendency. It seems that the subsidence which has been seen in a part of the northwest is calming from 2014 to 2018, but it seems that the subsidence area was seen in the DKI boundary part in the northwest and the area in the eastern suburbs (Sugarajaya district, near Bekasi district). Especially, the DKI boundary part in the northwest overlap with the period when the third terminal of Soekarno-Hatta International Airport started operation from 2014, and so the result suggests that the new subsidence is caused by groundwater pumping due to the increase in the construction of the airport hotel etc. Land subsidence monitoring wells are constructed in the Project. Based on the InSAR analysis results and discussions with the Counterpart, two locations are selected in Cengkareng and Cakung. As a structure, the double tube type is applied which is generally used in Tokyo considering its advantages that there is no mechanical or electric devices required resulting high durability. Based on the results of test borings three wells with different depth are constructed in each location in order to observe the layers which causes land subsidence (shrinkage happened). During the test boring, it is found that groundwater level becomes lower when drilling depth reaches 100 to 150m in Cengkareng site while it becomes lower and lower at 80m depth and at 160m depth. It may indicate the aquifers where groundwater is abstracted most. The construction works are conducted with intensive supervision by the Project Team and the counterpart and the world’s first construction method is applied through the discussion among the contractor, the supervisor and the counterpart. Beside the activities mentioned above, holistic approach is applied for the Project, and some pilot activities are on-going in the selected critical zones based on the discussion in Joint Coordination Meeting. And at the end of Project, action plan and implementing framework are expected to be formulated. (End)
Publication Year: 2020
Publication Date: 2020-01-03
Language: en
Type: article
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