Rainfall Makes Cheonggye Stream Toxic

Contaminants, including oil residue and dirt, flowed into the Cheonggye Stream on the morning of June 8, when it rained regionally for 30 minutes.

Citizens voiced concerns about the stream maintenance, as a 6.5-millimeter rainfall caused a large fish kill.

The Seoul Metropolitan City (SMC) admitted faulty stream maintenance, saying, “We have no countermeasures against rain for a short period like the one on June 8, while continued rain can resolve pollutants.”

When it rains more than four millimeters per 10 minutes, gates of rainwater pipes, which contain rainwater to prevent surrounding areas from being inundated, are automatically opened.

If the rain stops just after the gates are opened, contaminants that flowed into the Cheonggye Stream are carried down, affecting fish.

On June 8, when it rained 4.5 millimeters per 10 minutes, among 249 water gates, 10 gates up the pipes had been opened.

Kim Seok-jong, head of the Cheonggye Stream Maintenance Center, said, “There was no problem with fish in the Cheonggye Stream on June 10 and 11 when it rained around 40 millimeters in Seoul. It is an issue that fish died en masse due to rain which was neither heavy nor small.”

The SMC is planning to announce a measure to minimize damage to fish sooner. The criteria for water gate opening may be intensified from four millimeters per 10 minutes to five or six millimeters so that the water gates do not open for a medium rain. Simulations are underway to determine the appropriate number.

Dong-Ki Sung esprit@donga.com