Surveying three-dimensional perspectives of the flow structure around the bridge pile depending on the vegetation pattern distribution

Abstract

Modeling techniques have enabled us to understand how to protect vital infrastructures using nature-based solutions. In this research, we demonstrated that by selecting a specific vegetation pattern distribution upstream of the pile as a nature-based solution, we could reduce the amount of scouring around the bridge piles. This is essential to avoid the negative impacts that occur after landslides, flash floods, or mudflows close to populated areas. This solution can mitigate the global problem of bridge failure. To achieve this goal, an Acoustic Doppler Velocimetry device (ADV) was used to measure the velocity components in an experimental channel with a 90 cm width, 15 meters long, and 60 cm high. Two different widths of vegetation were used: the overall vegetation, with a 90 cm width, and the patched one, with a 10 cm width, positioned upstream of the bridge pile. In the case of using patched vegetation, a 36% reduction was observed in the amount of scouring around the bridge pile compared to the free-vegetation case, showing the positive effect of using vegetation to reduce scouring. In both cases, the amount of negative Reynolds shear stresses decreased when the presence of vegetation was registered. Using octant analysis, the overall vegetation was shown to convert internal events into external ones in front of the pile. However, in the case of using patched vegetation, internal events were also observed in addition to external events. Patchy vegetation changed the transverse direction of outward vortices from internal to external. In the presence of patchy vegetation, the dominance of the inward event decreased sharply. The presence of vegetation in the flow path affected some bursting events and, as a result, reduced scouring. The results showed that each of the used vegetation models has a different effect on bursting events, and these events can affect the amount of scouring hole depth.