Impacts of Bridge Piers on Scour at Downstream River Training Structures: Submerged Weir as an Example

Abstract

River training structures are conventionally used to improve river stability and ecological conditions and to protect the upstream instream infrastructures from scour and erosion. A submerged weir is a typical river training structure usually built downstream of bridges for grade control. Flow over the weir can cause local scour, destabilizing both the structure and the trained river reach. It is therefore important for safe design to estimate the scour accurately and understand the effects of an upstream bridge pier on local scour at submerged weirs. This study describes experiments on the scour process at a submerged weir with an upstream bridge pier, varying the distance L between the two. In this study, 56 experiments were conducted using uniform coarse sand with a median grain size d 50 = 0.85 mm in a sediment-recirculating flume. For clear-water scour, the experiments showed that the bedform induced by the pier scour process creates a scour-and-fill process upstream of the submerged weir; and the upstream pier can also affect the scour downstream of the submerged weir, through two mechanisms: (i) upstream sediment replenishment and (ii) flow section constriction. The mechanisms (i) and (ii) can reduce and increase the downstream clear-water scour depth at the submerged weir, respectively. For live-bed scour, a pier upstream can reduce and increase the scour depth upstream and downstream of the submerged weir, respectively. Based on the experimental data, the dependence of the scour depth at the submerged weir on L is evaluated.

Numerical Analysis of Flow Behavior in a Rectangular Channel with Submerged Weirs

“…Submerged weirs are training structures with the function of improving navigability. These structures are also built to improve river stability and ecological conditions and to protect the upstream in-stream infrastructures from scour and erosion [14]. Previous studies attempted to analyse the flow behaviour above such training structures using CFD.…”

Sediment bed morphology in the wake of wall mounted deformable plate

“…The presence of distinctive 3D wake flows are often considered to be precursors for sedimentary bed morphology. Numerous studies have focused on the fundamental fluid-sediment interaction mechanisms for flow over finite square or circular cylinders [29,30]. McKenna Neuman conducted a series of experiments [10,31,32] on wind flow over short wall mounted obstacles of various geometries and concluded that local erosion patterns are correlated to the regions of coherent vortical structures.…”

Structural Properties of the Static Armor during Formation and Reestablishment in Gravel-Bed Rivers

“…The armor layer protects the riverbed and is important for the stability of the river channel. However, the flood control requirements can increase flow discharge and break the armor layer, inducing bed incision as well as scour at river banks or instream structures [1][2][3][4][5]. Stable armor layers commonly occur in poorly-sorted gravel-bed rivers when the imposed bed shear stress is less than the critical shear stress needed to initiate particle motion on the bed surface [6][7][8].…”