Influence of dam failure flow on water level in dam and the underwater breach topography

Due to the young geology, unique climates, and location in the Pacific Rim seismic zone, complex sediment disasters frequently occur in Taiwan.  After the Chi-Chi earthquake in 1999, more than ten landslide dams appeared in the mountain regions with disaster potential to the neighbor.  The process of landslide dam breach is complex, often accompanied by abundant sediment and floods that cause damage to the downstream environment.  Therefore, analyzing the landslide dam breach process is an important subject.

The study area is located in Landau Creek in Huisun Forest, Nantou County.  Landao Creek is a tributary of the Beigang River, a potential debris flow torrent.  The soil and rocks on site were used to build a natural dam for the dam failure experiment.  The process of dam failure was recorded with cameras and UAVs.  In order to understand the relationships between the dam and the water level, some water pressure gages were set inside the dam and in upstream to measure the water pressure over time.  Because it is difficult to observe the change of the underwater breach with the naked eye during the dam failure process, triaxial sensors were placed in the dam body to determine the change of dam breach by recording the time when the sensors were scoured away from their original position.  The analysis showed that the groundwater level gradually increased during the dam failure, and the downward trend would slow down over time.  The underwater breach shape was similar to a parabolic or trapezoid shape.