Impact of banquette structures on a sandy beach profile: Laboratory experiments

A novel experiment using a mimic banquette is presented. This study investigates the morphodynamic effects of different banquette configurations on a sandy beach under erosive wave conditions. Following a six-hour exposure to irregular waves with significant heights of 0.6 metres, different banquette configurations were tested to assess their role in coastal protection. Wave height evolution, bar parameters, total sediment transport and shoreline position were used to evaluate the coastal protection efficiency of the banquette. The results of the study indicate that all banquette structures effectively reduced the flow of water towards the upper beach, limiting run-up and mitigating backshore erosion compared to a beach without protection. Larger banquettes provided greater stability by forming an active berm that restricted water passage, allowing minimal infiltration. In contrast, smaller banquettes, which allowed overtopping, influenced localized erosion and accretion near the shoreline, while still protecting the upper beach. Morphological changes were primarily observed near the shoreline, while sand profiles in the offshore bar region remained stable due to minimal variations in incident wave heights. Banquette structures also induced wave reflections at their toe, increasing localized erosion, particularly for those preventing overtopping. The findings demonstrate the effectiveness of banquette structures in reducing coastal erosion, with performance variations depending on the size and overtopping capacity. The study offers valuable insights for the optimization of coastal protection strategies, guiding the design of nature-based defences to mitigate erosion impacts on sandy shorelines.