The amount of water and sediment that rushed from the barrier lake was too much for the barriers protecting Guangfu Township, an official said.
A barrier lake on the Mataian River (馬太鞍溪) overflowed on Tuesday not due to hydroengineering faults, but primarily because of the unexpected volume of water and mud, Ministry of Economic Affairs Water Resources Agency Director-General Lin Yuan-peng (林元鵬) said in Hualien County’s Guangfu Township (光復) yesterday, where the Executive Yuan’s Forward Coordination Task Force was inspecting the damage.
The task force found a 300m opening in a southern section of the barrier blocking the lake, which was presumably the primary outlet of the lake, Lin said.
Debris from the Mataian Bridge, which was destroyed in the flood, obstructed the flow of the water, leading to multiple breaches of the dike between the river and the town, he said.
After the government was made aware of the barrier lake, which formed in July, it launched operations to mitigate the effects should it break, including stacking sandbags and removing nearly 400,000 tonnes of earth from the riverbed, he said.
However, the volume of water released, as well as the sediment it carried, was too much for the barriers protecting the town, Lin said.
Reporters asked Lin if three open levees had caused the flooding of the town.
He said that the levees were opened to drain water from urban areas and the severity of the flooding was primarily due to the dike being topped.
Separately, former minister of the interior Lee Hong-yuan (李鴻源), who specialized in water resources, said that he was approached by Minister of the Interior Liu Shyh-fang (劉世芳) two weeks ago to convene a team to help monitor the risks posed by the barrier lake.
Lee said that his team was tasked with facilitating the evacuation of 8,000 people, a plan based on simulation data, and urged other residents to also vacate the area,
The region remains at high risk of flooding for at least another week, he added.
Had the Ministry of the Interior not acted according to the data, the damage and death toll would have been far greater, Lee said.
Asked whether destroying the barrier that formed the lake would be a solution, he said that such an operation would be impossible, tantamount to blowing up an entire mountain.
There is no standard for handling barrier lakes, which pose significant threats in most countries, he said, adding that in many situations, mitigation efforts are unable to resolve problems born of natural forces.
Meanwhile, Liu on Sunday spoke with Executive Yuan Secretary-General Xavier Chang (張惇涵), which was when the decision was made that residents along the Mataian River should be evacuated, a source said.
The Forestry and Nature Conservation Agency and the National Fire Agency had contacted the Hualien County Government nine and 10 times respectively to urge it to expedite the evacuation, the source said.
When President William Lai (賴清德) visited the Hualien Emergency Operation Center on Monday, he instructed local governments to work with the central government to “ensure that evacuation of the Mataian River area when necessary,” the source said.
Moreover, Premier Cho Jung-tai (卓榮泰) had facilitated evacuation plans for the area and asked the Hualien County Government to enact them, they added.
The emergency operation center had remained on a Category 2 alert and only raised it to Category 1 after the water topped the dike, they said.
The 14 people known to have died at the time were in areas that the Central Emergency Operation Center had designated for forced evacuation, the source added.
