Scour below Pipelines in Waves

This paper presents the results of an experimental investigation on scour below pipelines exposed to waves. The effect of lee‐wake of the pipe is the key element in the scour process, and it is demonstrated that the Keulegan‐Carpenter number is the main parameter that governs the equilibrium scour depth. Based on the presently available data, a design equation is established, relating the equilibrium scour depth to the Keulegan‐Carpenter number for the live‐bed situation and for a pipe in contact with the bed. The latter equation indicates that the equilibrium scour depth normalized with the pipe diameter is proportional to the square root of the Keulegan‐Carpenter number, the proportionality constant being 0.1. The effect of Shields parameter on the final scour depth is found to be quite weak. It is also found that the surface roughness of the pipe imposes practically no influence on the scour process. The pipe position with respect to the bed appears to be an important parameter in determining the equilibrium scour depth.