hankyoreh

A view down the stairs of an apartment building in Seoul’s Gwanak District at which three people died when the torrential rains caused their semi-basement dwelling to flood on the night of Aug. 8. (Baek So-ah/The Hankyoreh)

The Seoul metropolitan government has decided to build deep rainwater tunnels in six neighborhoods of Seoul that are prone to regular flooding, including Gangnam District. The city is also moving to ban the construction of apartment buildings that include semi-basement units and to phase out current semi-basements over the next 20 years.

“I will be working to resume construction on the rainwater storage and drainage facilities in six flood-prone parts of the city, a project that was paused in 2011,” Seoul Mayor Oh Se-hoon said in a position statement on Wednesday.

Oh intends to build rainwater tunnels around Gwanghwamun and the Dorim Stream — including the area around Gangnam Station that was heavily damaged by flash flooding earlier this week — by 2027 and in the Sadang neighborhood of Dongjak District and in parts of Gangdong District and Yongsan District by 2030.

That project will involve upgrading sewers and building small rainwater reservoirs and rainwater pumping stations. Seoul estimates the project will cost 3 trillion won (US$2.3 billion).

“There was absolutely no flooding damage in the Yangcheon area, which has a rainwater storage and drainage facility that can process precipitation at a rate of 95-100 mm an hour and hold 320,000 tons [of rainwater]. Since the Gangnam area lacks such a facility, it’s only capable of processing precipitation at a rate of 85 mm an hour, which led to this large-scale flood damage. I will push ahead with the project even if it must be [funded by] the issuance of municipal bonds,” Oh said.

Rainwater tunnels are massive pipes that are buried below downtown areas to hold water during downpours while moving it away from the normal sewers. During an earlier stint as mayor, Oh had planned to install those facilities in seven parts of the city after a deadly landslide on Mount Umyeon in July 2011.

But his successor, Park Won-soon, adjusted all the projects except the one in the Sinwol neighborhood of Yangcheon District. Park had thought it would be more efficient to expand underground drainage facilities or build “smart tunnels” that could ordinarily serve as underground roadways but be converted to reservoirs during heavy rainfall.

“As we saw in Yangcheon District, we can expect such facilities to have the ability to reduce the scope of damage or reduce the duration of flooding,” said Lee Yeong-ju, a professor in the Department of Fire and Disaster Prevention at the University of Seoul.

But Park Chang-geun, a professor at Catholic Kwandong University and head of the Korea Water Society, pointed out that there was “almost no rain damage in Gwanghwamun,” an area that doesn’t have a rainwater tunnel.

“Furthermore, a smart tunnel is already being designed for the Sadang neighborhood, and it doesn’t make sense to build a separate rainwater tunnel. As for Gangnam Station, construction is already complete on a drainage tunnel that now just needs to be connected with outlets in the area. There will be plenty of time [to build a rainwater tunnel] after we’ve gauged the effectiveness [of the drainage tunnel],” Park said.

Seoul also rolled out safety measures for households living in semi-basement units. The measures say that building permits will no longer be granted for apartments that contain basement or semi-basement units.

“While a 2012 revision of the Building Act allowed officials to reject residential building permits for basement units in flood-prone areas, more than 40,000 basement and semi-basement units have been built since then. We need to keep people from living in basement and semi-basement units whether or not they’re in flood-prone areas,” the city government said.

Semi-basement units currently in use will be gradually eliminated over the next two decades. To accomplish that, the city will encourage the rezoning of residential basement units and give tenants an opportunity to move to public housing. Currently, there are around 200,000 basement and semi-basement housing units in Seoul.

The ruling People Power Party came out in support of Oh’s measures.

“Given the need to swiftly install the rainwater tunnels, we have strongly requested that the requisite funding be included in the budget bill for next year,” said Park Hyeung-soo, the party’s floor spokesperson, following deliberations between the party and the government on Wednesday.

By Jeon Jong-hwi, staff reporter

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