Field velocimetry for sediment transport studies in water and air

Rates of sediment transport predicted by models differ significantly from field observations in both aeolian and underwater environments.Refinement of predictive models requires high quality ground truth data to discern if the discrepancy between models and field observations lie in a given model's ability to properly represent the physics of motion, or if our field observations are inadequately sampling the sediment transport process.Identifying the sources of error can only partially be achieved in a laboratory wind tunnels or wave flumes.The limited length and scale of turbulence recreated in wind tunnels do not follow those of natural boundary layer conditions that exist on a windy beach.Similarly, wave amplitudes and spectral content resulting in seabed sediment transport can only be recreated in limited scope in a wave flume or oscillating water column.Ruggedised point measurement tools are available for measuring fluid velocities in a field environment but are of limited spatial and temporal resolution.Here we describe the adaptation of two high resolution full field velocimetry techniques that fully transition laboratory methods to quantify sediment transport by wind and waves for use in field environments.To measure subaqueous sediment transport, we developed a Stereo Time Resolved Particle Image Velocimetry (SPIV) system that utilizes submersible enclosures for remote operation in an undersea environment at depths of up to 15 meters for a period of several weeks.The system was deployed off the coast of O'ahu near the Makai Research pier.To measure sediment transport by wind in a natural boundary layer, we developed a Time Resolved Volumetric Velocimetry system based on Shake-the-Box 4D Particle Tracking (STBPT).We deployed this system on a secure beach at NASA Wallops Flight Facility in Wallops Island, Virginia.Adapting valuable and sensitive equipment to measure sediment transport by waves and wind in an outdoor environment presents substantial technical and logistical challenges.This paper will describe the two systems mentioned above including design considerations, technical 1019 Lecture spciale innovations, experiences gleaned from the measurement campaigns and examples of data obtained.