3rd AUN/SEED-Net Regional Conference on Natural Disaster (RCND2015) 25 - 26 September 2015, De La Salle University, Manila, Philippines
ASSESSMENT OF NATURAL HAZARDS AFFECTING THE DELTA CITY OF JAKARTA H.Z. ABIDIN1, H. ANDREAS1, I. GUMILAR1, T.P. SIDIQ1 and J.J. BRINKMAN2 1 Geodesy Research Group, Institute of Technology Bandung, Jl. Ganesha 10, Bandung, Indonesia, E-mail :
[email protected] 2 Deltares, Delft, Netherlands
Contributions Jakarta is the capital city of Indonesia with a population of about 10.2 million people, inhabiting an area of about 660 square-km. It is located within a deltaic plain and passes by 13 natural and artificial rivers flowing through it to Java sea. In the last three decades, urban development of Jakarta has grown very rapidly in the sectors of industry, trade, transportation, real estate and many others. This rapid urban development has caused several negative externalities, such as: extensive conversion of prime agricultural areas into residential and industrial areas, significant disturbance to main ecological function of the upland of Jakarta area as a water recharge area for Jakarta city, and increase in groundwater extraction due to development of industrial activities and the high population increase. In turns Jakarta is then prone toward a few natural hazards mainly land subsidence and flooding. The recent larges flooding in Jakarta occurred in 1996, 2002, 2007, 2013, 2014 and 2015. The results obtained from leveling surveys, GPS surveys and InSAR technique over the period between 1982 and 2014 show that land subsidence in Jakarta has spatial and temporal variations. In general the typical observed subsidence rates are about 3 to 10 cm/year, and can be up to 20-25 cm/year at certain location and certain period, as shown in Table 1. Table 1. Observed land subsidence rates in Jakarta; after (1) No.
Method
1
Leveling Surveys
2 3
GPS Surveys InSAR
Subsidence Rates (cm/year) Min - Max Typical 1-9 3-7 1 - 25 3 - 10 1 - 28 4 - 10 1 - 12 3 - 10
Observation Period 1982 - 1991 1991 - 1997 1997 - 2014 2006 - 2010
In general, the impacts of land subsidence in can usually be seen in the forms of cracking of permanent constructions and roads, changes in river canal and drain flow systems, wider expansion of coastal and/or inland flooding areas, and malfunction of drainage system. Several areas along the coast of Jakarta already have experienced tidal flooding during high tide periods. These coastal flooding usually occurs in the areas with relatively large subsidence rates. Subsidence in the areas along the rivers which are flowing throughout Jakarta, will also worsen the impacts of riverine flooding. The changes in river canal and drain flow systems and malfunction of drainage system due to land subsidence will also aggravate the flooding. If the land subsidence affected areas as derived by Leveling, GPS and InSAR are compared with the flooded areas in Jakarta (2), it can realized that there are some spatial correlations between land subsidence and flooding affected areas. Example shown in Figure 1 shows that the water depths in the flooded areas during 2007 flooding are also spatially coincided with magnitudes of land subsidence in the period of 2000 to 2011. However, more quantitative picture of the correlation between land subsidence and flooding in Jakarta still needs to be elaborated and modeled.
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Water depth (m) of 2007 Flooding
GPS-derived subsidence (2000-2011)
Figure 1. Spatial correlation between GPS-derived land subsidence (2000-2011) and flooding area in Jakarta (2007), after (2) The losses due to these natural hazards in Jakarta are indeed enormous. Related infrastructural, social and environmental costs due to direct and indirect impacts of land subsidence are economically quite significant, and can not be under estimated in sustainable urban development. In this regard for example, the planning, development and maintenance costs of building and infrastructures in the affected areas are usually much higher than the normal situation. The collateral impact of coastal subsidence in Jakarta, in the form of coastal flooding during high tides is also quite damaging (2). This repeated coastal flooding in several areas along the coast, will deteriorates the structure and function of building and infrastructures, badly influences the quality of living environment and life (e.g. health and sanitation condition), and also disrupts economic and social activities in the affected areas. Inland subsidence should also has an impact on inland flooding phenomena in Jakarta (3), since it will theoretically lead to expanded coverage and deeper water depth of flooded (inundated) areas (2). The losses due to inland flooding in Jakarta are also significant since it affects many economic related activities in the city and surrounding regions. Keywords: Jakarta, Urban Development, Land Subsidence, Flooding, Leveling, GPS, InSAR References 1. 2. 3.
H.Z. Abidin, H. Andreas, I. Gumilar, and B.D. Yuwono, Proceedings of the XXV FIG Congress, Kuala Lumpur, Malaysia, 16-21 June 2014. H.Z. Abidin, H. Andreas, I. Gumilar, and I. R. R. Wibowo. Proceedings of IAHS, Vol. 370, 15-20, 2015. P. Texier, Disaster Prevention and Management, 17(3), 358-372, 2008.
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