Combining Individual Scour Components to Determine Total Scour

The impact of lateral flow contraction on the rock plucking process under sub‐critical flow conditions

“…The 17 experimental cases and the measurement results are summarized in Table 2. To understand rock plucking under lateral flow contraction, parameterizing the role of turbulence around the bluff structure (oscillating horseshoe vortex, increased Reynolds stress in the vicinity of the structure, and increased vorticity due to the horseshoe vortex and separated shear flow) is a formidable task (Chua et al, 2019; Fang et al, 2017; Stoesser et al, 2008; Sturm et al, 2018). However, at the most basic level, it has been hypothesized that the contribution of the turbulence is an increase in TKE at the bed that provides the energy for initiation of rock motion and sustained rock plucking, because TKE is an indicator that accounts for the impact of local turbulence generated by the local vortex structure and the separated shear zone around an instream structure (Chrisohoides et al, 2003; Hong et al, 2015; Lacey & Rennie, 2012; Lefebvre et al, 2014).…”

“…The elevated level of TKE associated with local flow acceleration and local turbulent structures near the obstruction is interconnected with the degree of flow contraction between the approach and contraction sections (Chua et al, 2019; Hong & Abid, 2019; Melville et al, 2021; Sturm et al, 2018). Thus, it has been hypothesized that the value of in Table 2 may itself vary with the effect of flow contraction.…”

“…Forming along the structure in the flow direction behind the separation point was a flow recirculation area that originated from the separation point and expanded in the transverse direction as it moved in the downstream direction. Along the boundary of the recirculation area, a reaction between slow‐ and fast‐moving flow within and outside of the recirculation area, respectively, was responsible for the formation of a strong shear layer (Sturm et al, 2018). Shear flow that curves away from a structure at the point of separation experiences increasing velocities, cross‐stream velocity gradients, and higher turbulent energy over the defined area (Chua et al, 2019; Melville et al, 2021; Yang et al, 2021).…”

“…Under severe flow contraction, the block was prone to plucking quickly because the higher value of TKE max / resulted in a larger amount of prompt upward displacement, a critical element in the initiation of rock plucking (Bollaert & Schleiss, 2003; Lamb et al, 2015; Li et al, 2016). With a sufficient amount of upward displacement, the block was able to escape by dynamic impulsion induced from fast‐moving flow around the structure (Sturm et al, 2018). The results shown in Figure 11 indicate that rock plucking occurs near the obstruction even under lower value of centreline shear stress because of local amplification of the stress near the edge of the obstruction induced by turbulent flow structures.…”

Local Scour at Complex Bridge Piers in Close Proximity under Clear-Water and Live-Bed Flow Regime

“…As a result of the insufficient knowledge, people usually tend to design with large safety redundancy when dealing with real engineering practices, leading to excessive cost and push the original budget much higher. In addition, it is also worth mentioning that the interaction between bridge piers and other bridge foundation components, e.g., the abutments, has also been studied by Oben-Nyarko and Ettema [29] and Sturm et al [30,31]. They found that the extent and depth of the abutment's scour hole is much greater than that of a nearby pier and thus the scour aggravation caused by pier proximity is usually negligible.…”