TAIPEI (Taiwan News) — The Water Resources Agency on Sunday defended the use of open levees along Hualien’s Mataian Creek, saying flooding in Guangfu Township in September 2025 was caused by extreme weather and a landslide dam breach, not the levee system, per CNA.
Critics had attributed the flooding to the intermittent, open-levee design, saying it may have worsened the disaster.
The agency said heavy rainfall from Typhoon Ragasa, combined with the collapse of a landslide dam on Matai'an Creek, led to the flooding. It stressed the incident was unrelated to the open-levee system.
In a press release, the agency said open levees are a common flood control method used in both Taiwan and Japan, where the system is known as “Kasumi-tei.” The design uses staggered embankments rather than a single continuous levee or channel.
The agency said the purpose of staggered levees is to allow floodwater to spill into nearby rice paddies and ponds instead of being forced into a single channel, which can cause rapid rises in water levels and flow intensity. By dispersing water into surrounding areas, pressure on the main channel is reduced, and floodwaters can return downstream more gradually after heavy rains subside.
The agency said the Guangfu levee along Mataian Creek was designed to withstand rainfall events expected once every 100 years. The open levee on the right bank meets this protection standard and was built in accordance with flood control plans. Its elevation aligns with designated flood levels and does not constitute a structural breach.
An assessment by the National Federation of Hydraulic Engineers of Taiwan found that overflow from the landslide dam breach reached 8,860 cubic meters per second, far exceeding the levee system’s protection capacity of 2,040 cubic meters per second, per the press release.
The agency said the surge was not a typical flood but a high-energy flow carrying large volumes of soil, sand, boulders, and debris. The resulting “super flood” destroyed Mataian Bridge and caused extensive damage to levees on both sides of the river. It said such an event could not have been prevented by the existing levee system or other man-made flood control infrastructure.
The agency added that sediment deposits following the breach raised the riverbed by an average of three to five meters, with total accumulation exceeding 10 million cubic meters, requiring significant resources to remove and prevent secondary disasters.
While respecting compensation claims from affected families, the agency said the disaster was primarily the result of extreme natural conditions and not related to the open-levee design. It urged the public to rely on accurate information and avoid spreading misinformation.
