TAIPEI (Taiwan News) — In a wide-ranging interview, National Taiwan University civil engineering professor Colin Stark discussed the risks and remediation efforts surrounding landslide dams in Hualien County, which have drawn public attention following recent disasters.

Stark said the best way to analyze such events is through what engineers call a classic one-dimensional “dam break” problem, in which a dam is considered to fail instantaneously and fluid dynamics are used to calculate the downstream impact.

Researchers from Stark’s program were tasked with conducting such an analysis of the Mataian Creek landslide lake, delivering their findings just four days before the catastrophic failure earlier this month.

“There was a very recent reassessment of the flood risk. It was extremely accurate and timely, made just days before the failure,” Stark said. “So the science worked.”

He said researchers calculated a peak discharge of 15,500 cubic meters per second, which proved accurate given the area’s friction and geological characteristics. For comparison, flows of about 1,000 cubic meters per second are already considered hazardous.

“The real question is why people still die,” he said. “The forecasts were right, there was time to act, but local governments often report that people were ‘evacuated’ when in reality they were just warned. That’s a huge difference.”

Stark explained that landslide dams are inherently unstable because they are composed of loose material such as boulders, sand, and mud. Many natural dams fail during heavy rain as erosion carves channels through the structure, producing sudden and dangerous downstream floods.

“Landslide dams like this usually don’t last very long,” Stark said. “If they’re created during storms, they tend to wash away during the same storm unless they’re extremely large. But big ones from major earthquakes or typhoons can stick around for a long time — though they’re always unstable.”

Controlled drainage preferred

As for mitigation, Stark said controlled excavation, such as cutting a drainage channel over the top of the dam to gradually lower water levels, is the safest and most effective approach.

“The typical strategy is to cut a drainage channel over the top of the dam so the water can flow out gradually,” he said. “You want to drain the lake in a controlled way, not have it suddenly spill over the top.”

However, such efforts are challenging due to the remote terrain. “You need excavators and heavy machinery, but access is really difficult,” he said. “It can take days just to build roads to reach the site.”

Stark said overtopping, when rising water begins to flow over a dam’s crest, represents the most dangerous moment.

“Once a dam starts to overtop, that’s the most dangerous time,” he said. “The water begins cutting into the top and eroding the downstream face, that’s when collapse usually happens. People sometimes think overtopping is good, that the water is just spilling out, but it’s not. Once it overtops, the erosion happens very quickly.”

Explosives not a solution

Stark cautioned strongly against using explosives to clear debris, describing it as an unnecessarily risky and counterproductive measure.

“Dynamiting it would be a terrible idea,” he said. “That’s the rough equivalent of dropping a nuclear bomb into a hurricane. It sounds dramatic, but it doesn’t solve the problem. It just throws debris everywhere and risks triggering an uncontrolled flood wave.”

He added that precision blasting is not a substitute for careful, staged drainage and heavy excavation work.

“The sensible approach is to evacuate everyone downstream and then drain the water gradually by cutting a channel,” he said. “You can’t stop property damage, but you can stop people from dying.”

Stark referenced the Vajont Dam disaster in Italy in 1963, when a massive landslide sent a flood wave over a dam and killed nearly 2,000 people. “The dam survived, but everything below it was wiped out,” he said.

Fragile dam structure requires action

Stark said catastrophic flooding risks have been reduced since the initial breach of the Mataian Creek barrier dam, though the structure remains fragile.

The dam is composed primarily of Miocene-era sedimentary rock, typical of the Central Mountain Range, making it weaker than other formations in the area.

By contrast, the Swallow Grotto barrier lake was formed within marble rock, which he said is far stronger and more resistant to failure. “The gorge is carved in marble, which is very strong rock, that’s why the walls are so steep and narrow,” he said. “The river cuts deeply, but the rock holds up. You don’t usually get big landslides in marble, though earthquakes can still loosen things.”