Analysis of the characteristics of the development of the dam breach during overtopping

Extreme rainfall events induce landslides and debris flows and large amounts of sediment could block river channels and form dam lakes. Floods release after dam breach cause serious disasters and change channel forms for downstream areas. Therefore, understanding the basic characteristics of the dam breach is a key issue for disaster mitigation.

Field dam breach experiments were conducted in the Landao Creek, Huisun Forest, Central Taiwan to investigate the characteristics of the development of breach during overtopping. The HTC01 sensors with accelerometers were placed inside the dam, and the characteristics of the signal generated by current flows were used to explore the process of dam breach. We also set pneumatic water gauges and capacity soil water content sensors to monitor the changes about water content and porosity. The grain size distribution of the dam was derived from in situ grain size sampling. Three-dimensional surface velocity distribution was obtained from image analysis. Combining these analyses could explore the shape of breach and the headward erosion rate.

The results indicate that the shape of breach tracked by the HTC01 sensors is similar to trapezoid. There was no obvious downward and lateral erosion in the initial stage of the breach. After the dam crest being completely eroded by the water flow, the downward erosion starts to develop until a certain extent, and then the lateral erosion begins. This erosion cycle repeats until the dam breach completed.