Experimental investigation of turbulence generated by wave interactions in the nearshore using particle image velocimetry

Measuring velocity fields in the coastal nearshore region is difficult due to water level fluctuations, high wave energy, drastic accelerations, and bubble interference with instruments. While point measurements exist in this region, little is known about the behavior of turbulence generated by breaking waves. This study uses a mobile, minimally invasive particle image velocimetry (PIV) setup to investigate the wave-breaking region of a large fixed-bed flume (1:30 slope). A streamlined acrylic box depressed and stabilized the free surface below the breaking waves, allowing a laser light sheet to illuminate particles, which were captured by a high-speed camera. We investigated bore-backwash and breaker-backwash interactions at multiple locations for solitary waves, double solitary waves, and monochromatic waves. Data were collected using traditional PIV (f_s= 100 Hz, Δt = 2.25 ms) and time-resolved PIV (f_s = 333 Hz), capturing both the fastest parts of the flow and flow accelerations, respectively. Bubbles were created as waves collapsed, obscuring particles in some frames. Ongoing analysis explores whether the bubbles passively follow the flow and can serve as tracers to maintain continuous velocity fields for turbulence analysis. This work aims to improve our understanding of turbulence in the wave breaking region and its role in nearshore processes. This small-scale yet highly energetic process is poorly understood but is critical to predicting mechanisms of sediment transport.