Scour Effects on Coastal Defense Structures. Examples from the Portuguese West Coast

Abstract

Different types of coastal defense structures are used to protect shoreline against coastal erosion and flooding. Many of these structures were built on sand or soil material that can be easily removed or eroded by the action of waves, currents or combined waves and currents. The loss of bed material, either from beneath the structure or nearby the structure, can occur rapidly, over short time spans (during a storm event), or gradually, during a lengthy time span (months to years), [1]. In both cases, scour can significantly affect the structure functionality and stability and, in some situations, may lead to an imminent collapse and failure of some sections or all the coastal defense structure. The physical processes involved in scour are quite complex and usually are significantly influenced by the characteristics of the structure, the local wave climate and water depth, the currents regime and the bed material characteristics in the vicinity of the structure. Because scour related damages on coastal structures is often difficult and expensive to repair, the possibility of damage resulting from scour should be addressed during its project. Regarding this issue some limitations of available design guidance are pointed out [2]. During the structure lifetime periodic inspections should be carried out. In this paper, several scour related damages on coastal defense structures located on the highly energetic Portuguese West coast will be reported and analyzed. The (potential) mechanisms of failure will be identified and possible measures to reduce the consequences of that phenomenon will be presented.