Experimental Investigations of the Impact of Tsunami-Like Hydraulic Bores on a Square Vertical Structure. II: Local Scour | Journal of Waterway, Port, Coastal, and Ocean Engineering | Vol 149, No 1

AbstractThe effects of tsunami-like dam-break bores on the evolution of scour around a square structure were experimentally investigated for bores propagating over a saturated bed. The bores were generated using a rapid-release gate installed inside a hydraulic flume with a relatively wide range of still-to-impoundment depth ratios and two different bed slopes. The time history of the scour formation was recorded for the front and side walls of the structural model for both supercritical and subcritical hydraulic bores. The magnitude of the maximum scour for various test conditions was linked to the still-to-impoundment depth ratios and bed slopes. The time variations of scour rate and Shields parameter were generated from scour profiles and the results were then used to study the incipient motion of sand particles around the structural model concerning different tsunami-like bore heights and two bed slopes. The analysis of the presented experimental results revealed that the deepest scour hole and the greatest scour rate were observed for the case of the horizontal beds. On the other hand, the critical Shields number was smaller for the case of the inclined bed tests, causing the earlier erosion of bed materials in the inclined bed tests compared with the horizontal ones. These experimental results revealed that regardless of the bed slope, the front and side corners of the structural model had higher scour depths than the centers of the front and side walls. Furthermore, owing to subsequent deposition, the lowest ratio of the equilibrium scour depth to the maximum scour depth was observed in the side corner of the model, although this ratio was greater in the horizontal bed compared with the case of the inclined bed test. In addition, for both sub- and supercritical flows, the scour rate showed a directly linear correlation with an increasing still-to-impoundment depth ratio in the front and side corners.



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