Measuring flow velocity and sediment transport with an acoustic Doppler current profiler

An acoustic Doppler current profiler (aDcp) measures three-dimensional velocity profiles within the water column using the Doppler shift principle, whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration. The aDcp offers many advantages over traditional single-point current meters and sediment samplers, including deployment from a moving launch, a single instrument for both velocity and sediment transport measurements, profiles of three-dimensional velocity and suspended sediment and the ability to map an entire flow field. Limitations of aDcps include a large sampling diameter close to the bed, coarse measurement of vertical velocity, fragmented bottom track records, a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport, and sensitivity of the acoustic backscatter to particle size.