Seoul Metropolitan Government's Water Reclamation Planning Division will equip existing manholes in some of the city's most flood vulnerable areas with nets and other screening devices to prevent people from falling into the holes if the manhole covers get swept away in severe flooding. Courtesy of the Seoul Metropolitan Government

By Ko Dong-hwan

The Seoul Metropolitan Government has decided to retrofit its manholes in the city with screens after they proved vulnerable to serious flooding during the recent floods earlier this week.

The Water Reclamation Planning Division under the city government's Water Circulation Safety Bureau said Friday that they will first retrofit manholes in city areas hit hardest by the severe disaster. When underground sewage tunnels overflowed during the torrential rains, the hydraulic pressure inside intensified, knocking open or even shooting into the air the cast-iron manhole covers that weigh 40 kilograms. As the streets flooded, some manhole covers were swept away by the water, and two people fell or were sucked into the open manholes.

This past Monday night, two siblings ― a man in his 40s and a woman in her 50s ― in the Seocho-dong area of Seoul's southern Seocho District were sucked into a manhole while walking on the knee-deep flooded road amid rainfall of 120 millimeters per hour.

Emergency rescuers searched for the siblings down the sewage tunnel using a submersible robot. The body of the man was found dead two days later, inside another manhole some 1.5 kilometers away from the original manhole he had fallen into. His sister was also found dead on Friday, in a stream near Dongjak Subway Station in Dongjak District, over five kilometers away from where she originally fell.

These deadly manhole incidents occurred despite the safety lock feature of the manhole covers, which was supposedly designed to keep the covers in place even under high water pressure from flooded underground sewage tunnels. But when the city saw 120 millimeters of precipitation per hour, the safety feature proved to be useless.

The city's water division said they will use nets or steel screens to block the spaces below manhole covers as a safety measure to prevent any fatal falls the next time the covers get blown off and swept away. The authority will start retrofitting the manholes within this year.

"The city areas prone to flooding will be the first to see their manholes improved. We expect the measure to prevent human casualties from manhole cover dislocation," said Han Jae-hyun, Seoul's deputy mayor for administrative affairs.

There are nearly 600,000 manholes scattered across Seoul alone. Six people are missing and 13 people have died during this week's torrential rains and flooding that lasted for days starting Aug. 8. A band of rain-saturated clouds first hit the country's capital region of Seoul, Incheon and Gyeonggi Province, then moved southward to the country's central regions of the Chungcheong provinces.