The influence of underwater embankment properties on breaching failures

Flow slides are underwater slope failures that occur in fine sandy deposits at many river and coastal locations. They occur when large amounts of sediment move down an underwater slope in a relatively short time. This can be triggered by a variety of factors including erosion by tidal flow, local changes in water pressure, or human interventions such as dredging. Flow slides can remove an entire dike or dune section, which poses a severe threat to flood defences and human life. In the Netherlands there is much research on this subject because two thirds of the country are vulnerable to flooding. Despite the case histories of known flow-slide events, the processes operating during an active flow slide are not well understood. Flow slides are difficult to observe and monitor: the events start underwater and are only noticed once the failure reaches the subaerial bank. For this reason, though the final geometries of the flow slides are well known, the trigger mechanism and the actual development of the slides over time have seldom been witnessed. This dissertation provides a deeper understanding of flow-slide processes, focusing on the properties of embankments and their influence on the type of failure. This aim was accomplished using different approaches, a 2D flume tank and the Eurotank basin, demonstrating, and quantifying the processes that contribute to the phenomenon.