A note on acoustic measurements of turbulence, suspended sediment, and bed forms in mobile-bed experiments

Abstract

Mobile-bed laboratory measurements allow observation of interactions between turbulent sediment-laden flows and irregular, non-stationary bed topography. Water in mobile-bed experiments is typically clouded by suspended particles, complicating the use of optical and laser based measurement techniques. In such conditions, acoustic techniques can be used to measure turbulence, suspended sediment transport, and bed topography; however, these procedures also have unique challenges. Here, the effect of suspended particles on acoustic Doppler turbulence measurement, the effect of particle size on acoustic measurement of suspended-sediments, and a method for statistically describing bed topography (measured acoustically or otherwise) are addressed. It is found that suspended particles have a small effect on Reynolds stresses measured with an acoustic Doppler velocimeter and that those effects could be minimized by excluding data collected with the highest and lowest acoustic amplitudes. The effect of particle size on acoustic backscatter amplitude is most strongly pronounced for particles smaller than 0.3 mm. Semivariogram analysis is shown to be a viable method for analyzing complex bed topography produced by mobile-bed experiments.