Wave-Current Turbulence over Nature Rough Seabeds (Iii)

Hydrodynamics and turbulence play an important role in modeling and monitoring the geological, biogeochemical, and biological processes in nearshore environments. It is difficult to have a quantitative study due to the complex process of wave-current interaction and flow and three-dimensional topography interaction. Because of the difficulty of measuring turbulent kinetic energy in a wavy environment, most studies have confined to study the dissipation rate of turbulent kinetic energy in the surface boundary layer or in the bottom boundary layer in the last two decades, or study the turbulent kinetic energy budget in current-alone flows without effects of waves. Based on the up-to-date literature review and our recent efforts, wave-current turbulence in nature rough seabed of coastal environments are largely unexplored. As a result, we propose to study the wave-current turbulence over nature rough seabed in fields. In the recent published and submitted works, we have shown the ability and experiences to perform high-quality field experiments to observe the turbulence in shallow waters in the challenging coastal zone where waves and currents coexist. In the proposal, field experiments and data analysis will be conducted to explore the mechanisms driving the turbulent mixing over the nature rough seabed over coral reefs at Hobihu and DongSha atoll. The results from the two field sites will be compared. A suite of instruments including pressure sensor, velocimetry, wind sensor, and video camera will be deployed along a line in the cross-shore direction to measure the wind, waves, currents, turbulence, and wave breaking over these reefs. Field experimental data observed from the coral-reef experiments at Hobihu and DongSha atoll will be analyzed. In summary, this proposal is seeking to investigate the following scientific questions: Hobihu coral-reef experiment: (1) Length scale of turbulent eddies in a shallow coral reef, (2) Flow structure and drag parameterization above and within coral-reef colonies, (3) Effects of heterogeneous distribution of coral colonies on form-drag dissipation. DongSha experiment: (1) Vertical structures of flow and turbulence in sparse coral bommies in DongSha atoll.