Combined measurements of velocity and concentration in experimental turbidity currents

Three different sets of experimental turbidity currents were run in which velocity and concentration were measured simultaneously, for several different heights above the bed. One set with cohesive sediment had an initial volumetric concentration of 16% kaolinite, and the other two sets with non-cohesive sediment had concentrations of 28% and 4% silica flour. Velocity was measured at 104-122 Hz using an Ultrasonic Doppler Velocimetry Profiler and concentration was measured at 10 Hz using an Ultrasonic High Concentration Meter. The similarity of changes in velocity and concentration at the same measurement heights are described and it is shown that the similarity depends on flow concentration and position in the flow. The measurements are analysed using cross-correlations and wavelet analysis. Velocity measurements are compared with analytical solutions for flow around a semisphere and flow around a half body. Measurements and analyses indicate that turbulence is diminished by stratification, decoupling of regions where turbulence is generated and by reduction of vertical flow in the turbidity currents.