Flow hydrodynamics and scour around bridge pier during tsunami propagation in coastal rivers

Tsunami propagating into a coastal river can severely damage hydraulic structures including bridge piers as reported during past tsunami events. Hence, in the present study, laboratory experiments are performed initially by generating tsunami bores on to a wet bed in a 24m long, 0.8m wide wave flume and later in a 12mx0.5mx0.465m recirculating channel to maintain a time scale of 1:6 required as per Froude scaling to observe reliable scour depth at the pier model. Three-dimensional flow velocities (using rigid bed) and scour patterns, depths (using mobile bed) around a circular bridge pier model were obtained to understand the scour process. Finally, the scour depth due to tsunami bore is compared to empirical steady flow scour estimations. Therefore, the present study proposes new scour design standards for bridge piers or vertical evacuation towers which are already inundated by the first wave of tsunami.