Measuring Bedload Sediment Transport with an Acoustic Doppler Velocity Profiler

Abstract

International audienceAcoustic Doppler velocity profilers (ADVP) measure the velocity simultaneously in a linear array of bins. They have been successfully used in the past to measure three-dimensional turbulent flow and the dynamics of suspended sediment. The capability of ADVP systems to measure bedload sediment flux remains uncertain. The main outstanding question relates to the physical meaning of the velocity measured in the region where bedload sediment transport occurs. The main hypothesis of the paper, that the ADVP measures the velocity of the moving bedload particles, is validated in laboratory experiments that range from weak to intense bedload transport. First, a detailed analysis of the raw return signals recorded by the ADVP reveals a clear footprint of the bedload sediment particles, demonstrating that these are the main scattering sources. Second, time-averaged and temporal fluctuations of bedload transport derived from high-speed videography are in good agreement with ADVP estimates. Third, ADVP based estimates of bedload velocity and thickness of the bedload layer comply with semi-theoretical expressions based on previous results. An ADVP configuration optimized for bedload measurements is found to perform only marginally better than the standard configuration for flow measurements, indicating that the standard ADVP configuration can be used for sediment flux investigations. Data treatment procedures are developed that identify the immobile-bed surface, the layers of rolling/sliding and saltating bedload particles, and the thickness of the bedload layer. Combining ADVP measurements of the bedload velocity with measurements of particle concentration provided by existing technology would provide the sediment flux

Bedload Velocity and Backscattering Strength from Mobile Sediment Bed: A Laboratory Investigation Comparing Bistatic Versus Monostatic Acoustic Configuration

“…The cell deformation at the end of the measurement range (R) the bistatic geometry provides an equal spatial distribution of the pulse scattering, eventually permitting profiling of the bedload velocities through the active layer, without significant influence of the immobile bed below [13].…”

“…In the last few decades, various videography techniques have been developed to investigate the behavior of bedload particles, mostly on a small scale and in controlled conditions, involving analyzing individual particle tracks and velocities [6][7][8][9], denoted as particle tracking velocimetry (PTV). Additional image processing techniques, such as optical flow and image differencing, have been successfully applied to calculate mobile bed velocity, the surface concentration of mobile particles, and even the shape of particles in reasonably set-up conditions [10][11][12][13][14]. However, image processing techniques are limited to laboratory applications due to light conditions, small sampling areas, large data storage requirements, and relatively difficult installation.…”

“…Bistatic systems, often referred to as acoustic Doppler velocity profilers (ADVP), can deliver detailed velocity profiles close to the bed and estimate the concentration of the material resuspended above the bed [28]. Another laboratory study demonstrated that ADVPs could depict several cells of bedload velocities inside the active layer [13]. Consequently, bistatic acoustic systems allow detailed measurements of bedload transport characteristics, clearly distinguishing between the volume scattering of mobile particles and the surface scattering of the immobile sediment bed.…”

Pulse Coherent Doppler Profiler Measurement of Bedload Transport

“…These results do however raise the potential for measuring the bedload component of transport building on the established methods for suspended load measurements. Indeed, such bedload measurements have provided encouraging results in recent laboratory studies utilizing purpose-built sonar systems (Blanckaert et al, 2017;Froman et al, 2018Froman et al, , 2019Naqshband et al, 2017;Revil-Baudard et al, 2015Stark et al, 2014;P. Thorne et al, 2018).…”

Localized scour around setback abutment in compound channel

“…For larger water depth, the flow velocity was measured using ADVP which could be used to measure instantaneous components of velocities in three dimensional directions with a high accuracy of ± 0.5%. Many researchers such as Song et al (1994), Rennie et al (2002), Chen (2014) and Blanckaert (2017) had used ADVP to measure velocity, turbulence and coherent structure of flow. The Acoustic Doppler Velocimeter profiler (ADVP) was a cheaper instrument for velocity measurements compared to Particle Image Velocimeter (PIV) (Emadzadeh, 2014).…”