Dune erosion and beach evolution under monochromatic waves: An experimental study

Supervisors: Ana M Ferreira, Ryan Mulligan (Queen’s University, Kingston, Canada)
According to the Nature Conservation International Union (2006), 60% of the world’s population or 3.8 billion of people live less than 100 km from the coast. With this number increasing year after year, buildings and infrastructures are constructed closer and closer to the shoreline. To understand sediment erosion/accretion phenomenon in detail and to prevent the threat of coastal hazards to society, research into coastal processed is needed. Dune/beach systems are really complex and play the role of natural defence against flooding, for example, from extreme events, coupled with high waves and storm surges. Several studies have been conducted to help understand the impact of storms on the coasts for different conditions, the present report supplements the work of Berard, (2014) to examine dune erosion, using a 35.5 m long, 0.9 m wide and 1.2 m deep flume at the Queen’s University Coastal Engineering Research Laboratory (QUCERL). Using regular (monochromatic) waves that propagate toward a 0.65 m high sand dune, erosion under two different regimes (overwash and inundation) that correspond to different water level elevations are investigated. Observations were collected using six wave probes located along the flume, and bathymetric measurements were collected at selected times using a laser line. In previous experiments, erosion in the overwash regime was investigated. This study is the first to examine the process of dune erosion in the inundation regime in laboratory. The results for the both regimes indicate a continuous retreat of the dune crest but also the formation migration of sand bars formed by the eroded dune material. In the case of the inundation regime, erosion rates are much higher and final beach profiles are very different than for the overwash regime, suggesting that the behaviour of the dune/beach system is very different under extremely high surface waves and storm surges.