Measuring Suspended Sand Concentration in Rivers from Acoustic Backscatter: Current Possibilities and Limitations
Abstract
The use of sonars (e.g. Acoustic Doppler Current Profilers, ADCPs) is among the most promising alternatives to physical sampling for monitoring a suspension of sand particles in rivers. Accurate acoustic measurement of sand suspended sediment concentration (SSC) has already been achieved: i/ in marine science for monitoring sand suspensions near the ocean bottom; ii/ in laboratory flume experiments for monitoring sand SSC load. River applications are less advanced however. So far, quantitative methods require calibration data (i.e. physical sampling) and/or specific deployment conditions (i.e. suspension homogeneity along the acoustic beam, which is usually achieved in a side-looking horizontal deployment configuration). Based on various measurement campaigns in the Rhône River (France) using a multi-frequency sonar, we discuss some existing limitations to the development of a quantitative method designed for monitoring sand SSC in large rivers from the water surface, i.e. in a vertical (down-looking) deployment configuration. These limitations include instrument issues (power, frequencies, sensitivity, calibration), poor understanding of some physical processes (impact of air micro-bubbles, turbulence, small number of dominant scatterers), limited accuracy of sediment acoustic response modelling (backscatter and attenuation), performance of inversion methods and intrinsic environmental limitations (small particle target strength vs. high transmission losses). Whereas an efficient technique for quantifying river sand suspensions is not yet available, we finally present some interesting qualitative results that can already be extracted from sonar backscatter data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP31C2367V
- Keywords:
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- 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1856 River channels;
- HYDROLOGYDE: 1860 Streamflow;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY