Preliminary Assessment of Scalar Transport across the Sediment-Water Interface of Rippled Beds

Sylvia Rodriguez-Abudo1, Juan Carlos Vargas Martinez2, Edwin Aponte2 and Brandon Santaliz3, (1)University of Puerto Rico Mayaguez, Department of Engineering Sciences and Materials, Mayaguez, United States, (2)University of Puerto Rico Mayaguez, Department of Mechanical Engineering, Mayaguez, United States, (3)University of Puerto Rico-Mayaguez, Department of Mechanical Engineering, United States
Abstract:
Important biogeochemical, ecological, and potentially hazardous processes occur at the sediment-water interface (SWI) in coastal benthic boundary layers. Resolving the transport of substances across the SWI requires a fundamental understanding of the physics governing advection and diffusion processes in this environment. Parameterizing these processes in the nearshore is not a trivial task, as the combined effect of unsteady wave forcing and bedform-induced coherent motions result in fluxes of momentum that can drastically vary in time and space. Moreover, the presence of non-uniform mass sources can provide additional across-ripple variability, further complicating the depiction of scalar fluxes in this setting. Characterizing these processes with common acoustic techniques can be challenging, as point/profile measurements are unable to provide a depiction of the instantaneous intra-ripple dynamics. New laboratory observations of the velocity and scalar fields at unprecedented intra-ripple resolution aim at elucidating the complex mixing structure resulting from the combined effect of unsteady hydrodynamic forcing and bedform-induced turbulence. An oscillating boundary layer apparatus consisting of a sediment tray controlled by a stepper motor has been built at UPRM’s wave flume facility for this purpose. This effort presents preliminary data obtained from laser-based non-invasive techniques consisting of a combined Particle Image Velocimetry (PIV)/Planar Laser Induced Fluorescence (PLIF) system, all oscillating with the moving frame. Near-bed velocity field are resolved with the PIV, while scalar concentrations are quantified with the PLIF and rhodamine dye in order to assess the bedform-induced turbulent structures and their connection to scalar fluxes. The knowledge gathered through this study will aid in the development of parameterizations of mass transport in coastal benthic boundary layers including contaminants, nutrients, and biogeochemical processes.
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