Effectiveness and Limitation of Coastal Dykes in Jakarta: The Need for Prioritizing Actions against Land Subsidence

Abstract

Jakarta has been experiencing severe land subsidence over the last few decades. A questionnaire survey of local inhabitants revealed that seawater is already overtopping coastal dykes and flooding a vulnerable community along Jakarta's waterfront. The present study projects coastal floods around Jakarta until the year 2050 to understand the long term effectiveness of proposed dykes under continuing rapid land subsidence scenarios. This is done through a hydrodynamic model that considers land subsidence, sea-level rise, and tides. The analysis confirms that, if high enough, coastal dykes will help to prevent flooding, though their effectiveness will eventually disappear as land subsidence continues. For example, a 3-m dyke, which is expected to be sufficiently high to cope with present-day conditions, could completely lose its ability to stop floods by the year 2040. Moreover, higher dykes can also bring about other problems, because if they are overtopped, they actually prolong flooding, essentially trapping a higher volume of water inland. On the other hand, a small 1-m dyke can be expected to stop coastal floods if land subsidence can be stopped. This study demonstrates that actions to stop land subsidence would be the most effective countermeasure to mitigate coastal floods from the middle of the 21st century onwards, emphasizing the need to prioritize such actions among the range of countermeasures being proposed for Jakarta.

A review of structural approach to flood management in coastal megacities of developing nations: current research and future directions

“…Furthermore, a hydrodynamic modelling study by Takagi et al (2017), which aims to understand the long-term effectiveness of proposed dikes under continuing sea-level rise, tides and rapid land subsidence scenarios in Jakarta, shows that the effectiveness of using higher flood defence will gradually disappear over time. Xian et al (2018) raised concern that current flood mitigation measures need to be stepped up to account for the dynamics of future climate and sea level rise in coastal cities.…”

“…However, results from Yin et al (2015) show that hard engineering measures have limitations, and merely increasing the height of flood defences does not always address the problem, but rather transfer risks from one place to another, as water will backflow to upstream locations to cause increased water level and potential inundation in surrounding neighbourhoods. With sufficient evidence now highlighting the limitations of flood defences in CMDN, Takagi et al (2017) recommended that from the middle of the 21st century onwards, actions to stop land subsidence should top the list of the most effective countermeasures against coastal floods in cities such as Jakarta. This recommendation by Takagi et al (2017) is useful because it emphasises the need for future researchers, funding bodies and the governments of CMDN to work together to explore innovative and viable solutions to the problem of land subsidence.…”

“…With sufficient evidence now highlighting the limitations of flood defences in CMDN, Takagi et al (2017) recommended that from the middle of the 21st century onwards, actions to stop land subsidence should top the list of the most effective countermeasures against coastal floods in cities such as Jakarta. This recommendation by Takagi et al (2017) is useful because it emphasises the need for future researchers, funding bodies and the governments of CMDN to work together to explore innovative and viable solutions to the problem of land subsidence.…”

Survey Tool for Rapid Assessment of Socio-Economic Vulnerability of Fishing Communities in Vietnam to Climate Change

“…Exposure thresholds were identified by dividing the range of projection given at the national level into three ranges, with the actual exposure for each site being assessed based on local projections. However, instead of deriving the exposure thresholds of sea level rise from national projections, the three ranges of exposure were based on engineering judgement by the authors (based on studies on adaptation to ground subsidence, see [33][34][35]).…”

Port Adaptation to Sea Level Rise: Lessons From Present Examples of Land Subsidence

“…In order to better understand the consequences of future sea level rise the authors have analysed the effects of two instances land subsidence that have taken place in the 20 th and early 21 st century, and the adaptation measures that ports and other low-lying areas have adopted in the northern Japanese region of Tohoku following the 2011 Earthquake Tsunami, and Jakarta in Indonesia (where groundwater extraction has been inducing rates of subsidence of 10-20cm per year in several parts of the city, Takagi et al, 2017). To date, the authors are not aware of any other work that has systematically attempted to learn from real examples of land subsidence as a proxy to study the effects of SLR on ports, despite a number of calls for more research to be done on the subject (Becker et al, 2013).…”