On February 2, Park Won Soon, mayor of Seoul, visited a site replete with sinkholes in Tokyo, Japan. He said, “The financial self-reliance of Tokyo is similar to that of Seoul at around 80%, but Tokyo has been receiving approximately KRW 500 billion — 9.5% of its total budget — of financial support from the government since 2008, making it possible to renovate the entirety of the city’s antiquated sewer system, a root cause of sinkholes. Therefore, as Seoul City can not handle this issue without the government’s assistance, the Korean Government’s expansion of the scope of its subsidies is urgently required.”
As the Seoul Metropolitan Government (SMG) needs a total of KRW 4.05 trillion to renovate the deteriorated drainpipes, stretching about 3,700km, in areas with sinkholes, it is impossible to improve the sewer system within a short time; thus, the SMG is slated to first replace some 932km of drainpipes more than fifty years old. However, the SMG still needs financial assistance in the region of KRW 256 billion.
The budget necessary in 2015 is about KRW 230 billion, so the SMG asked for KRW 100 billion from the government, excluding Seoul City’s budget of KRW 130 billion, but only KRW 10 billion was allocated for renovations. In 2015, KRW 15 billion was earmarked, but KRW 5 billion was set aside for research on sewer systems; therefore, the budget for the renovation was merely KRW 10 billion.
As an attempt to come up with preventive measures, the SMG is planning to renovate antiquated drainpipes, purchase state-of-the-art exploration devices for underground exploratory activities, and use private exploration services (500km annually, 1,500km every three years).
<Tokyo’s large-scale renovation of its outdated drainpipes and exploration activities using cutting-edge devices…less than 1% possibility of sinkholes leading to accidents>
In the case of Tokyo, due to poorer geological conditions than Seoul, the effects of earthquakes, and deteriorated drainpipes, roughly 1,000 sinkholes used to be reported every year. However, the possibility of sinkholes leading to accidents is less than 1% now thanks to preventive measures, such as large-scale renovation of outdated drainpipes and exploration activities using state-of-the-art exploration devices.
About ten years ago, Tokyo analyzed the mechanism of sinkhole development and identified a considerable increase in the occurrence of submerged sinkholes resulting from drainpipes that were more than thirty years old. Tokyo City has since then been actively renovating its outdated sewer system to avoid the reality of the ‘fourteen times increase in sinkholes within fifty years’ prediction should renovations not be conducted properly.
After extensively renovating the antiquated drainpipes, the percentage of sinkholes occurring has dropped drastically from 48% in 1999 to 28% in 2009. The total budgetary amount allocated for the management of Tokyo’s sewer system is KRW 6.95 trillion in total, ten times higher than Seoul at KRW 691 billion.
<Seoul, half the antiquated drainpipes more than 30 years old are located in areas prone to sinkholes; thus, they require immediate renovation>
On the contrary, in Seoul, the total length of drainpipes is 10,392km (as of December 2013), and among them, drainpipes older than 30 years account for about 48.3% or 5,000km. In particular, 3,700km of outdated drainpipes are located in alluvial layer-areas that are prone to sinkhole formation; thus, these pipes must be immediately renovated. According to last year’s research on submerged sinkholes in Seoul, the number of yearly cases involving either large or small sinkholes is around 681 (as of July 2014), and among them, sinkholes occurring due to Seoul’s antiquated sewer system take up about 85%.
(Based on the sewer system statistics in December 31, 2013)
|Less than 10 years||10 years ~20 years||20 years ~30 years||More than
Mayor Park said, “As Seoul City has acquired cutting-edge exploration technology by signing an MOU on support for countering sinkholes with Tokyo, and if the renovation of outdated drainpipes is carried out as planned, the damage caused by sinkholes will be minimized as soon as possible.” He also stressed, “As the damage stemming from sinkholes is tantamount to that of a disaster, active support from the government in consideration of the local autonomy’s budget deficit is desperately needed.”