Wave overtopping II

Recently, there has been a rise in the combination of green/hybrid solutions to coastal protection, but effects of natural systems on overtopping performance is uncertain. Accounting for numerous factors related to climate change, coastal protection systems have become vital for the survivability of coastal communities. Recently, large-scale (1:2) experiments were conducted at the Oregon State University Wave Research Laboratory throughout the summer of 2023 to measure the effects of mangroves on reducing overtopping of a coastal bulkhead or revetment. Experiments conducted at the United States Naval Academy in fall, 2023 will further investigate the overtopping performance of mangrove forests by replicating the OSU experiments at a 1:8 scale. The motive to conduct similar experiments at a smaller scale is to further understand the scaling requirement to formulate engineering guidelines, and to determine whether predictive equations can be accurately applied for these reduced scale tests.

This study investigates the flow velocity of extreme waves overtopping promenades. Using bubble image velocimetry (BIV), experiments were conducted in the scaled-down wave flume CIEMito at Universitat Politècnica de Catalunya. Post-processing of collected images determined flow velocities. The aim is to improve predictive models for wave overtopping onto structures with emergent toes found on sandy beaches, commonly used as promenades or waterfronts in urban coastal areas. Simulating extreme wave overflow in real random sea conditions, the NewWave theory correlates wave form and sea state attributes. Utilizing focused wave groups offers benefits including enhanced experiment replication, better measurement capabilities, and no wave absorption. One scenario from varying wave forces, tides, and coasts is presented-reflecting the Mediterranean Sea's micro-tidal environment with steep foreshores. The feasibility of non-intrusive methods like BIV for evaluating overflow flow velocity is explored, and initial findings are reported.

Many low-lying coastal urban areas in north-western Europe rely on a hybrid beach-dike coastal defense system against flooding, which consists of a low-crested impermeable sea dike and a long (nourished) beach in front that functions as a very/extremely shallow foreshore during storm conditions. Along the cross-section of this hybrid coastal defense system, storm waves are forced to undergo many transformation processes before they finally overtop the dike. Field measurements of all these processes at the same time are very challenging but necessary (i.e., no scale nor model effects), and crucial to evaluate design methodologies. This paper presents the field setup and the design features of an innovative research dike at Raversijde (RDR), unique in the world, which measures wave transformations, wave overtopping and impact; including a performance analysis of the RDR based on the first measured storms during winters '22-'23 and '23-'24.