Analysis of the development of the dam breach and flow field distribution during overtopping processes

A lot of flow causes a series of disasters and significant change of fluvial forms in the downstream area after the dam breach. Therefore, understanding the basic characteristics of the dam breach is a crucial issue. A field-scale experiment is conducted to investigate the relationship between the development process of the dam breach and the distribution of the flow velocity. Pneumatic water gauges are combined with Unmanned Aerial Vehicle (UAV) and digital elevation model (DEM) to obtain the water volume of the reservoir. The variation of water volume is used to analyze the discharge of the breach process. In addition, a new sensor, which is uniformly embedded in the each section of the dam, is invented to measure the variation of water depth in time distribution. Multiple UAVs are used to uninterruptedly measure DEMs of the dam breach during the entire experiment. Three-dimensional surface velocity distribution is obtained by Particle Tracking Velocimetry method (PTV) from these DEM data. The results show that the phenomenon of headwater erosion appears many times when the dam break. The surface velocity is dominated by the streamwise and vertical direction during the headwater erosion. Moreover, the highest velocity also occurs in the period of headwater erosion. The high-velocity flow causes the breach collapses from both sides to widen the available section for passing water. After comparing relationships among the outflow discharge, flow velocity, and breach area, the variation of outflow discharge is mainly controlled by the breach area.