Applicability of acoustic Doppler devices for flow velocity measurements and discharge estimation in flows with sediment transport

- We tested the effect of sediment transport on velocity measurement by acoustic Doppler.
- Analysis was based on field observations and flume experiments in Spain, Israel and the UK.
- Flow velocity was slightly underestimated with high suspended sediment concentrations.
- Flow velocity was significantly underestimated in the presence of coarse bedload particles.
- Starflow was found to be a valuable tool for discharge determination.

SummaryAcoustic Doppler devices (Unidata Starflow) have been deployed for velocity measurements and discharge estimates in five contrasted open-channel flow environments, with particular attention given to the influence of sediment transport on instrument performance. The analysis is based on both field observations and flume experiments. These confirm the ability of the Starflow to provide reliable discharge time-series, but point out its limitations when sediment is being transported. (i) After calibration of the instrument by the Index Velocity Method, the deviation from reference discharge measurements was < 20% at the 95% confidence level. (ii) In ungauged conditions at high flows, the Starflow was particularly useful in providing velocity data for approximating measurements of discharge. (iii) However, channel and flume experiments revealed the effects of mobilised sediment on velocity estimates: coarse particles (⩾ 150 μm) transported by way of saltation or as bedload caused a significant underestimation of velocity by as much as 50%; a slight underestimation (10-15%) was also observed when significant quantities of fine particles (⩽150 μm) were transported in suspension; this underestimation was shown to reach 20-30% when suspended sediment concentrations were very high (c. 50-100 g L−1).