Study of Breach Characteristics and Scour Pattern for Overtopping Induced River Dyke Breach

Pawan Bhattarai, Hajime Nakagawa, Kenji Kawaike, Hao Zhang

Wednesday 1 july 2015

11:45 - 12:00h at Africa (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 9F. Engineering - River

Every year flood discharge induced over topping flow through river dykes causes large damage to society, the environment and infrastructure. Although several researches have been conducted to understand embankment dam failure, there has been little focus on river dyke breaches. The dynamic lateral widening of the breach process, resulting flow and sediment hydro-graphs and the scour beneath or downstream of dyke are poorly understood. Therefore, elaborate laboratory tests were conducted to investigate the dynamic lateral widening process, breach characteristics and scour process. The experimental model is constructed in Ujigawa open laboratory, DPRI, Kyoto University, Japan. The 1 m long and 15 cm high homogeneous non-cohesive dyke is prepared along the 4 m long river flume placed parallel to the river flow and a small pilot channel is made at the center of the dyke to initiate the widening process. The entire process was recorded optically using video and three-dimensional cameras for detailed analysis of the breaching phenomena and the discharge of flow and sediments are measured downstream of dyke by collecting box method. For the determination of scour process, the foundation and the downstream bed are also made movable and equilibrium scour patterns are observed for two scenarios by laser measurement. The result indicates the important effect of particle size on the dynamic lateral widening process, breach discharge and the scour pattern. The result shows the impact of particle size on the widening process, resulting hydro-graph and scour pattern. Finer Sediment sizes show resistance to erosion and failure as well as higher scour at the foundation whereas coarser particles show opposite characteristics. The maximum scour depth is seen to follow approximately linear relation with the sediment size and the location of such scour is observed within the center of dyke towards the toe.