Experimental Investigation of Structural Width Effects on Bore-Induced Scour Depth around Walls

The present study examines the influence of the width of a structural element on local scour induced by tsunami-like inundation using dam-break bores through a program of laboratory experiments. The effect of bore characteristics on the local scour depth is also investigated. Based on the flow dynamics involved in the sediment transport processes, the authors initially hypothesized that the scour depth at the front face may primarily be driven by downward flow and horseshoe vortices, and that it would not vary significantly with structure width. Moreover, greater variation in scour depth was anticipated to occur at the upstream corners, where both horseshoe and lateral vortices contribute to the scour process. To test these expectations, time series of scour depth progression at the center of the front face and the upstream corners of the structural element were obtained using video cameras installed inside the structure. The results indicate that the scour depth at the upstream corner is less sensitive to the width of the structure, whereas the scour depth at the center of the front face is significantly influenced by the width. It is also demonstrated that the maximum scour depth recorded around the structure occurs at the upstream corners of the structure. An important finding of this study is that the final (residual) scour depth observed around the structure is shallower than the maximum scour depth observed during the inundation phase, highlighting the need to conduct further laboratory experiments to better understand the mechanisms of local scour development, rather than relying solely on post-tsunami field surveys.