Exploring the bifurcation between sedimentation versus scour onset below pipelines in unidirectional currents

The onset of tunnel scour beneath offshore pipelines has been previously documented to result from a phenomenon known as piping, in which the hydrodynamic pressure difference across a pipeline causes a sufficient pressure gradient within the soil under the pipe to result in floatation or suspension of downstream sediment particles. The change in propensity for onset of tunnel scour due to sedimentation around the pipe has also been previously noted. This paper explores the potential for predicting the cumulative sedimentation around a pipeline in unidirectional currents using a more fundamental approach than has previously been described in the literature. The results of this approach are compared to model pipeline experiments to see how well the predictions explain the observed changes in sedimentation and the associated effects of sedimentation on the potential for tunnel scour.