New lake formed by landslide in Taitung County, but Safety concerns about possible dam burst

The Taitung Forest District Management Office is monitoring a barrier lake formed after a landslide blocked a section of the upper reaches of the Danan River in Taitung county, and is warning residents and visitors to stay out of the riverbed below the newly-formed natural dam.

Residents of Dongxing Village, Beinan Township, Taitung County, alerted authorities after water in the Danan Stream had a sudden significant decrease in water flow on February 5. A subsequent investigation revealed that a landslide had occurred 12 kilometers upstream of the village, forming a landslide dam, also known as a barrier lake.

Taitung Forest District Management Office made an emergency survey on February 6, with the Disaster Prevention Research Center of Chenggong University taking drone aerial photography.

Residents in downstream communities became concerned on February 7 when a turbid water flow began to return to the stream, possibly signaling an impending dam rupture.

An aerial survey conducted from a helicopter yesterday, February 8 confirmed the preliminary judgement that downstream communities were in no immediate danger.

The survey found that rock and soil from a landslide had formed a dam around 25 meters wide, 20 meters high, and 50 meters long. Water storage capacity was estimated at about 25,000 cubic meters.

barrier lake formed by landslide, February 5, 2021
Rock and soil from a landslide had formed a dam around 25 meters wide, 20 meters high, and 50 meters long after a landslide February 5, 2021. Picture: Taitung Forest District Office.

The Taitung Forest District Management Office and the Disaster Prevention Center concluded that the barrier lake location was quite distant from the downstream communities, the amount of accumulated water was not large, and the downstream side had begun to seep. Therefore, there was no immediate danger to the villages.

However, signs need to be erected, and patrols initiated to prevent people entering vulnerable areas of the riverbed downstream of the barrier lake for the time being.

Dongxing Village is the home of the Taromak Tribe of the Rukai indigenous people, and the area is a popular destination for river tracers.

Satellite images will be used to monitor changes in the barrier lake, and the relevant information will be sent to the county government and Beinan Township Office.

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