Estimating sand concentrations using ADCP‐based acoustic inversion in a large fluvial system characterized by bi‐modal suspended‐sediment distributions

Abstract

Quantifying sediment flux within rivers is a challenge for many disciplines due, mainly, to difficulties inherent to traditional sediment sampling methods. These methods are operationally complex, high cost, and high risk. Additionally, the resulting data provide a low spatial and temporal resolution estimate of the total sediment flux, which has impeded advances in the understanding of the hydro‐geomorphic characteristics of rivers. Acoustic technologies have been recognized as a leading tool for increasing the resolution of sediment data by relating their echo intensity level measurements to suspended sediment. Further effort is required to robustly test and develop these techniques across a wide range of conditions found in natural river systems. This article aims to evaluate the application of acoustic inversion techniques using commercially available, down‐looking acoustic Doppler current profilers (ADCPs) in quantifying suspended sediment in a large sand bed river with varying bi‐modal particle size distributions, wash load and suspended‐sand ratios, and water stages. To achieve this objective, suspended sediment was physically sampled along the Paraná River, Argentina, under various hydro‐sedimentological regimes. Two ADCPs emitting different sound frequencies were used to simultaneously profile echo intensity level within the water column. Using the sonar equation, calibrations were determined between suspended‐sand concentrations and acoustic backscatter to solve the inverse problem. The study also analyzed the roles played by each term of the sonar equation, such as ADCP frequency, power supply, instrument constants, and particle size distributions typically found in sand bed rivers, on sediment attenuation and backscatter. Calibrations were successfully developed between corrected backscatter and suspended‐sand concentrations for all sites and ADCP frequencies, resulting in mean suspended‐sand concentration estimates within about 40% of the mean sampled concentrations. Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant across evaluations, suggesting that they could be applied to other sand bed rivers. © 2018 John Wiley & Sons, Ltd.

Application of Multifrequency Acoustic Inversions Using Three Horizontally Profiling ADCPs

“…• Figure S2 • Figure S3 • Figure S4 Correspondence to: D. Haught, dwhealdo@usgs.gov channels, so they provide some degree of spatial integration that is not possible with at-a-point optical instruments, although in wide rivers, hADCPs may ensonify only a fraction of the river width, requiring index relations to be developed between the hADCP response and sediment fluxes in the channel (Szupiany et al, 2019;Venditti et al, 2016).…”

“…Coupling observations of concentration, velocity, and/or discharge data provide an opportunity to estimate sediment fluxes. hADCPs measure profiles across river channels, so they provide some degree of spatial integration that is not possible with at‐a‐point optical instruments, although in wide rivers, hADCPs may ensonify only a fraction of the river width, requiring index relations to be developed between the hADCP response and sediment fluxes in the channel (Szupiany et al, ; Venditti et al, ).…”

Applying ADCPs for Long‐Term Monitoring of SSC in Rivers

“…Other than these technological issues, the acoustic methods proposed so far for SSC evaluation in rivers by means of ADCP do not consider organic matter, whereas relevant efforts were produced to account for PSD change. For example, (i) Wright et al (2010) discriminated silt-clay concentration from suspended sand using H-ADCP with horizontal aligned beams; (ii) Moore et al (2012) used H-ADCP for the monitoring of SSC during flood also suggesting multifrequency approach (i.e., an array of H-ADCP working at different frequencies) to eventually account for PSD change during flood; (iii) Guerrero et al (2013) used two ADCPs working at different frequencies on the same water column to provide profiles of SSC and corresponding mean diameter of suspended sand from the riverbed; and (iv) Szupiany et al (2019) estimated sand concentrations using ADCP by empirically decoupling the attenuation effect due to clay-silt concentration. All those methods considered the inorganic particles as the only reason for scattering and attenuation.…”

“…SSC monitoring stations are usually based in optical turbidity meters, however, more recently, the acoustic Doppler current profiler (ADCP) has become an extremely popular device for SSC assessment in rivers (Moore et al, ; Guerrero et al, ; Sassi et al, ; Szupiany et al, ; Venditti et al, ; Wright et al, ). This success was mainly due to the fact that the echoes profiling into the water column is a by‐product of flow discharge measurement by an ADCP.…”

Integrating suspended sediment flux in large alluvial river channels: Application of a synoptic Rouse-based model to the Irrawaddy and Salween rivers

“…2. Because it relies on the Rouse equation, it does not require the explicit calibration of the ADCP sonar equation (Kostaschuk et al, 2005;Darby et al, 2016;Szupiany et al, 2019) and different ADCP instruments can be used to obtain flow velocity measurements during different field campaigns. 3.…”