Bridge piers submerged in rivers and seas are among the structural elements most exposed to hydraulic effects, as they are continuously subjected to flow forces, waves, and water currents. Scour is considered one of the primary causes of bridge failures in waterways, as it leads to the loss of soil surrounding the foundations and reduces their load-bearing capacity. Local scour occurs when flowing water strikes the face of a pier, generating a downflow that moves toward the channel bed and then develops into a horseshoe vortex. This vortex erodes sediments around the pier foundation, forming a scour hole. The depth of scour is influenced by flow velocity, water depth, pier shape and width, and the characteristics of the bed sediments. In addition to local scour, general scour occurs as a result of changes in the bed elevation of the watercourse. Contraction scour, on the other hand, develops when the flow section is narrowed by the bridge and its piers, resulting in increased flow velocity and consequently greater sediment-transport capacity. In marine environments, additional forces such as wave loads and tidal currents affect pier stability and may increase scour depth. The effects of water are not limited to scour. Submerged bridge piers are also exposed to chemical attack and reinforcement corrosion caused by chlorides and sulfates present in saline water. In addition, impact loads may result from vessels and floating objects, while debris accumulation increases the lateral pressure acting on the pier and may intensify the risk of scour. To mitigate these risks, modern engineering practices employ protective measures such as riprap, concrete mattresses, and increasing the depth of piles. Streamlined pier shapes are also adopted to reduce the intensity of vortices around the structure. Furthermore, sonar devices and scour monitoring sensors are used to monitor changes in the channel bed, while Computational Fluid Dynamics (CFD) numerical modeling, using software such as ANSYS Fluent, is employed to analyze the distribution of flow velocities and pressures around bridge piers. In conclusion, understanding the effects of water on submerged bridge piers and predicting scour depth during the design stage, together with regular monitoring and preventive maintenance, are fundamental to ensuring bridge safety and maintaining their functionality throughout their service life. Presented by: Assistant Lecturer Farah Hameed Abdulkhader M.Sc. in Civil Engineering Source: Arneson, L.A. et al. Evaluating Scour at Bridges (HEC-18), FHWA-HIF-12-003, 2012.