Where does local scour typically occur?

Local scour typically occurs around an obstruction placed within the stream, such as bridge piers or pilings. This phenomenon happens because the presence of the obstruction disrupts the flow of water, leading to increased velocities and turbulence around the structure. As water moves around the obstruction, it can create eddies and low-pressure zones that remove sediment from the streambed, resulting in localized erosion. Understanding this process is crucial for bridge inspections and assessments, as ongoing scour can compromise the structural integrity of the bridge.

While obstructions like bridge piers commonly contribute to local scour, areas away from the channel edges typically experience less pronounced scouring effects. High sediment deposition areas generally align with regions of lower flow velocity, which do not facilitate the conditions necessary for local scour. Finally, while scouring may occur at the deepest part of the river, it is not classified as local scour unless it is specifically due to an obstruction enhancing that flow pattern. Thus, the focus on obstructions is key to understanding where and why local scour occurs.