Effects of Instrumented Bottom Tripods on Process Measurements

Abstract

Abstract The measurement and assessment of ocean bottom processes are important sources of information for understanding bedform evolution and sediment entrainment and for improving numerical models. Instrumented tripods have been used to investigate bottom boundary layer and sediment dynamics processes for several decades. In this paper, the effects of instrumented tripods on hydrodynamics and on the sea bed are investigated via numerical modeling and field data collected under moderate to strong tidal currents and mild surface waves. Under high currents, streamlines are modified and structure-induced vertical velocities are produced. To minimize this effect, a rotation of the three-dimensional current measurement under the frame is recommended. Acceleration of the flow under the frame is also significant (on the order of 10%–20%), which leads to an increase in bottom stress and can produce a large scour pit in energetic currents. Wave–structure interactions mainly increase turbulence near the frame. No significant wave effect has been observed near the bed, and scouring thus mostly relates to tidal currents.