Flood hydraulics due to cascade landslide dam failure

Landslide dams are usually unconsolidated and when they act to impound water, they are subjected to failure that triggers catastrophic flooding downstream. However, the flood hydraulics due to landslide dam failure has remained poorly understood and cannot be reliably predicted at present. Inevitably, this militates against effective flood risk management in areas prone to landslides. Extending the recent investigation of a single landslide dam failure and the resulting flood, here, we present an experimental and computational study on the flood flow induced by cascade landslide dam failure. A total of 12 runs of experiments are conducted in a flume of 80 m x 1.2 m x 0.8 m, with differing inflow discharge and dam composition. An array of 12 automatic water-level probes is deployed to measure the stage hydrographs along the flume. The coupled shallow water hydrodynamic model calibrated for cases of a single landslide dam failure is demonstrated to perform reasonably well for cascade landslide dam failure. Most notably, under appropriate conditions, the occurrence of streamwise progressive enhancement of the flood induced by cascade landslide dam failure is demonstrated. This features a higher risk of flooding downstream and therefore warrants careful consideration in flood risk management.