Bubble Image Velocimetry technique applied to wave overtopping flow characterization - challenges and opportunities

This study employs the Bubble Image Velocimetry (BIV) technique to characterise the flow velocity of individual extreme waves that overtop sea dikes. Physical experiments were conducted in the small-scale wave flume at the Marine Engineering Laboratory (LIM) of the Universitat Politècnica de Catalunya – BarcelonaTech (UPC). The primary objective was to develop more precise models for forecasting wave overtopping of structures with an emergent toe, which are typically found on sandy beaches and commonly utilised as promenades in urbanised coastal environments. The NewWave theory was employed to simulate extreme individual wave overtopping in a realistic random sea state: the utilisation of focused wave groups, as opposed to long-duration irregular wave time series, offers a number of advantages, including improved experimental repeatability and enhanced measurement capabilities due to greater temporal resolution. The present study examines the potential of employing the BIV technique for non-intrusive measurements and offers preliminary insights into the characterisation of overtopping flow velocity for the selected structure. The study demonstrates that overtopping flow fields are highly non-uniform, which challenges the assumptions of simplified models such as Boussinesq or non-linear shallow-water models. The BIV technique is therefore crucial in capturing the complex spatial and temporal variations in flow velocity.