Experiments on Tsunami-induced scour at circular and rectangular onshore structures

An experimental study of the scour development around circular and rectangular structures exposed to tsunami-induced flows is presented. Tsunami waves of different periods (147 s, 49 s, and 20 s) are generated in a flume at 1:50 Froude-scaled to analyse the scour processes around these structures. This study demonstrates how the geometry of the structure significantly impacts the scour depths. The results show that the rectangular structure experiences the maximum scour depth compared to square and circular structures, reaching approximately 0.16 m, this is primarily due to a strong vortex caused by the lateral boundary separation and greater blockage ratio. The evolution of scour depth was found to be time-dependent, with the maximum depth achieved early in the inundation phase and slumping observed towards the end of inundation, reducing the final scour depth by approximately one-third.

The analysis of the sediment’s angle of repose in scour processes shows that over-steepened slopes exceeding the natural angle (31°) were observed, reaching maximum slope angles of 84° on the side face and 70° on the front face of rectangular structures. Scour depths depended not on the magnitude of Shields parameter but rather on the duration for which the Shields parameter exceeded its critical threshold ($\theta >{\theta }_{cr}$). This research advances our understanding of scour mechanisms acting on different coastal structures, emphasising the influence of wave parameters, structural geometry, and sediment dynamics on scour mechanisms, offering a foundation for developing improved design guidelines for coastal infrastructure resilience against tsunami-induced scour.