[2020 National Audit] "K-water's Inaccurate Rainfall Forecast... Missed Golden Time for Discharge"

[Image source=Yonhap News]

[Asia Economy Reporter Kim Bo-kyung] In August, large-scale flood damage occurred downstream of Yongdam Dam, Seomjin River Dam, and Hapcheon Dam, and the Korea Water Resources Corporation (K-water) has been criticized for missing the golden time for pre-release due to inaccurate internal rainfall forecasts.

Lee Soo-jin, a member of the National Assembly's Environment and Labor Committee from the Democratic Party of Korea, revealed on the 19th that this fact was uncovered after analyzing data submitted by K-water.

K-water forecasts rainfall for the following month and plans dam releases accordingly. According to the dam operation plan disclosed by Lee, K-water predicted rainfall in August as "very low" in early and mid-August and "very high" in late August, judging it would be generally similar to the average year. However, the actual rainfall in August was 401.6 mm, which was very high.

Ultimately, K-water predicted low rainfall until mid-August and did not sufficiently conduct pre-release of the dams. When the dam water levels rose sharply, large-scale releases were made, causing massive flood damage downstream of the dams.

According to the official letter requesting approval for changes in dam release plans sent by K-water's Geumgang Basin Headquarters to the Geumgang Flood Control Office, on August 7 at 9 a.m., K-water forecasted rainfall in the upstream area of Yongdam Dam for August 7?8 to be 110?170 mm. This was slightly below the Korea Meteorological Administration's forecast announced at 5 a.m. on August 7, which predicted total rainfall of 100?200 mm (over 300 mm in some areas) for the Jeonbuk region (upstream of Yongdam Dam) during the same period.

However, the actual rainfall was much higher: 312.6 mm in Jangsu, 433.5 mm in Jinan, and 383.0 mm in Donghyang, all in Jeonbuk, exceeding K-water's internal forecast. As a result, K-water missed the last golden time for pre-release at Yongdam Dam, and when the dam water level reached the planned flood level at noon on August 8, a large-scale release of water equivalent to 2,900 tons per second was conducted.

Lee said, "Due to K-water's inaccurate rainfall forecast, the golden time necessary for pre-release was missed, resulting in large-scale flood damage. K-water bears significant responsibility in this matter." He added, "It is necessary to strengthen the cooperation system among the Korea Meteorological Administration, K-water, and the Flood Control Office to achieve more accurate rainfall forecasts," emphasizing, "Especially during the flood season, a more detailed manual on dam pre-release standards and procedures must be established."