Coastal and offshore structures
This chapter deals with the scour induced by wave and current action near pipelines, piles, vertical breakwaters, coastal defences and other submerged structures. The use of granular materials, such as riprap, for scour protection has a long tradition in both river and coastal engineering. Scour near coastal and offshore structures may be caused by currents and waves and may be either short-term or long term. J. L. Chao & P. V. Hennessy provide an order-of-magnitude estimate of the maximum scour depth under offshore pipelines that is due to currents only. Studies of scour around structures with more than one pile indicate that the formation of ripples is an important phenomenon. The general pattern of erosion depends on the wave and current direction with respect to the structure. Some additional information about scour prediction in the vicinity of coastal structures can be found in K. W. Pilarczyk & R. B. Zeidler.