Effects of a Rectangular Water-filled Canal on Bore Induced Horizontal Force Exerted on a Nearshore Structure

Following several extreme tsunami events such as the 2004 Indian Ocean Tsunami and the 2011 Tohoku Tsunami, which devastated coastal infrastructure in countries around the Indian and the Pacific shores, there has been an increased research effort into investigating tsunami-induced forces exerted on structures located near the coastline. Many researchers have investigated the mechanisms and characteristics of tsunami forces exerted on structures, and proposed mitigation countermeasures to reduce the impacts of tsunamis and subsequently minimize destruction. Forensic engineering post-tsunami field investigations have revealed that water-filled canals can reduce the inflow tsunami bore energy and act as an effective mitigation solution. However, studies on the effects of canals as mitigation countermeasures have been few and limited in scope, necessitating thus further research. This study presents a comprehensive experimental program conducted to investigate the effects of rectangular water-filled canal on mitigating tsunami horizontal force exerted on a square structural column. A rapid-release vertical gate was used to generate a tsunami-like hydraulic bore which propagated over a horizontal, dry, and smooth bed, further crossing over a rectangular water-filled canal, and subsequently impacting a vertical column. The time history of the bore depth at various locations along the flume, as well as the time history of horizontal force exerted onto the column were recorded. Moreover, bore propagation and interaction with the canal and column were analyzed using video-cameras positioned at different locations along the flume. Several parameters were found to affect the degree of force reduction, some of which were the water impoundment depth behind the gate which sets the characteristics of the bore, the canal width, and its depth. The obtained results indicate that the presence of a water-filled canal can significantly reduce the bore front velocity, and consequently, the maximum impact horizontal force exerted onto the column by more than 25%. These findings suggests that water-filled canals, as a potential solution, could effectively mitigate tsunami bores impact energy, reducing structural damage and potentially saving lives.