Seepage and rising water levels threaten landslide-formed dam in Taiwan’s Taroko Gorge

Authorities and geotechnical experts in Taiwan are closely monitoring an unstable natural dam that formed after a landslide in Taroko Gorge, Hualien County, warning that increasing seepage and rising water levels could trigger a potential failure.

The Forestry and Nature Conservation Administration’s (FNCA) Hualien Branch confirmed that the dam, which spans the Liwu River, is showing signs of structural weakness as seepage at its base intensifies. The newly created barrier lake behind the dam currently holds an estimated 2.7 million tonnes of water.

Officials said that overflow from the nearby Jinheng Tunnel and seepage through the dam’s lower layers have temporarily slowed further water accumulation. However, experts caution that continued heavy rainfall could accelerate erosion or overtopping, potentially causing a breach.

Li Meng-yen, chief coordinator of the Forward Coordination Post of the Central Emergency Operations Center, said the downstream river channel is wide enough to handle moderate overflow, lowering the immediate flood risk. Nevertheless, residents near the gorge have been evacuated and instructed to stay clear of the Liwu River corridor.

The dam body consists mainly of marble and granite fragments with limited silt content, making it less prone to sudden liquefaction or collapse compared with other sediment-rich natural dams such as the Mataian Creek barrier lake. Engineering teams from National Cheng Kung University and National Yang Ming Chiao Tung University have been deployed to conduct on-site stability and seepage analyses.

The FNCA and Directorate General of Highways have initiated construction of an 80-meter access road from the old Provincial Highway 8 to the Yanzikou Trail, allowing excavators and monitoring instruments to reach the site. Progress has been hindered by steep terrain and recurring rockfalls, and work crews are performing safety inspections before excavation begins. Authorities expect road access to be completed within three days, after which controlled excavation of the dam material can start.

Preliminary measurements place the landslide dam’s height at 54 meters, with a total deposit volume of about 400,000 cubic meters of rock. Its storage capacity of 2.7 million tonnes represents roughly 0.2 percent of the capacity of the Mataian Creek barrier lake.

Officials emphasize that while the risk of catastrophic failure remains moderate, continuous rainfall or seismic activity could alter conditions rapidly. Monitoring instruments are being installed to track water pressure, seepage rate, and deformation of the dam body in real time.