Authorities have identified a significant slope collapse as the main cause of the Matai’an Creek barrier lake breach. According to the Forestry and Nature Conservation Agency, several mountain slope collapses occurred, with the largest measuring 403 meters. This slope collapse played a critical role in the overflow that triggered flooding.
A detailed analysis by the agency’s Aerial Survey and Remote Sensing Branch (ASRS) revealed extensive terrain changes from the upstream mountains to the downstream creek bed. Using pre-event topographic data from the Ministry of the Interior, the ASRS compared the landscape before and after the breach. The most severe slope collapse took place near the top of the barrier lake.
Furthermore, large amounts of earth and rock accumulated in the midstream and downstream sections of the creek. This buildup raised creek bed levels by 40 to 50 meters, significantly altering the region’s topography. The findings came from a digital elevation model produced using Light Detection and Ranging (LiDAR) technology. The airborne LiDAR scan took place on September 25, two days after the breach.
The breach resulted from heavy rains brought by Typhoon Ragasa. The flooding caused by the lake overflow has been devastating, with 18 confirmed deaths and six people still missing. Rescue and recovery efforts remain ongoing, overseen by the Central Emergency Operation Center (CEOC).
Officials noted there are no signs of abnormalities in the lake dam structure or its water flow. However, the region continues to face risks due to large amounts of mud and sand clogging the downstream creek. Because of this, the CEOC has maintained a red alert for the area.
Meanwhile, reconstruction work is underway in Guangfu Township, the most affected location. Approximately 800 meters of levee repairs have been completed so far. This work accounts for nearly 28 percent of the total planned levee reconstruction. In conclusion, the slope collapse was a critical factor in the Matai’an Creek lake breach. Authorities continue to monitor the situation closely as recovery efforts proceed.
