Equilibrium Profile of Current-Induced Scour Around Submarine Pipelines

Submarine pipelines installed on seabed disturb the local flow field and bring imbalance in local sediment transport that leads to scouring. Local scouring can leave the pipeline unsupported in significant distances. The free spans of the pipeline are susceptible to damages arising from environmental forces or human activities. This paper presents results of experimental investigations on the equilibrium profile of the local scouring around the pipe due to unidirectional current. New equations are proposed for the prediction of the scour depth and width before installation of the pipe. It is evident from the experimental results that the equilibrium depth of the current-induced scour is a function of pipe diameter and Shields number. Also scour width at upstream and downstream of the pipe and the total width of the scour are investigated. The results are simplified in the form of diagrams for prediction of the scour depth/width in practice based on flow velocity, bed roughness condition and size of the granular materials. The results can be used either for the design purposes or for the calibration of numerical models. One of the results of this work is that the scour width at downstream of the pipe is about 2.5 times of the width at upstream.