The Morphological Evolution of the Breach Channel by Prototype Field Experimental of Landslide Dam

Landslide dam breach release the large amounts of water and sediment, which cause dramatic change in downstream channels. In previous studies, data collection from the landslide dam breach could be obtained from two sources. One is monitoring field cases and another one is the small scale laboratory tests. However, the prototype field experiment combined the advantages of both. The dam breach was more similar to real event in this experiment, which improved the shortcomings of the lab test including too small scale, over-simplified and the boundary effect. On the other hand, it also solves the problems of the incomplete and unrepeatable data collection in the field cases investigation. Therefore, the evolution of channel morphology caused by hydrological processes of landslide dam breach was analyzed by using the pressure gauges, Acoustic Doppler Velocity Profiler (ADCP), photographic monitoring, topographic measurement of 3D Lidar in the Landao Creek, the Huisun Experimental Forest, Central Taiwan in this study. The peak outflow was affected mainly by the breach cross section. Therefore, the velocity of the breach cross section was measured by ADCP and its development was analyzed by the bathymetry function of ADCP combined with images analysis. The downstream sediment concentration affected by the sediment loss of the breach cross section was estimated by taking the water sample during the dam breaching. In addition, this study observed the deposition after breaching experiment, which was compared with the channel morphology after natural extreme hydrological events, by topographic measurement. The result of water sampling showed that the sediment concentration raised from 1.57% upstream to 6.13% downstream of the dam. A fourfold increase of sediment carrying capacity by flood caused serious deposition in downstream and the deposition height was about 10 cm.