Author(s): Oriana Yon-Campaner; Maxime Lernould; Pierre-Alain Barraud; Guillaume Fromant; David Hurther

Linked Author(s):

Keywords: Wide-band ACVP; Two-phase sediment transport; Open channel flow; Bedload; Turbulence

Abstract: Benthic sediment transport in river and coastal waters shapes aquatic habitats, regulates nutrient and pollutant fluxes, and maintains the long-term ecohydraulic stability of fluvial, estuarine and deltaic systems. Accurate prediction of sediment transport flows—combining bedload and suspended load—is therefore essential for assessing habitat vulnerability and resilience to energetic flood events. Yet most existing experimental datasets were not obtained under such energetic conditions and rely on single-phase mixture approaches assuming negligible particle–fluid inertial lag (aside from settling velocity). These mixture -theory models (McTigue 1981; Guo and Julien 2001) and associated measurements (Revil-Baudard et al. 2015, 2016; Guta et al. 2022, 2024) limit our understanding of key benthic processes compared with recent two-phase fluid–particle modelling advances (Cheng et al. 2018; Salimi et al. 2021; Mathieu et al. 2022). As described by Finn and Li (2016), such geophysical sediment-laden flows involve turbulent two-way (dilute) and four-way (dense) couplings that remain poorly constrained experimentally. To address this gap, this study introduces new sediment -transport experiments performed under steady, uniform, hydraulically rough open-channel flows spanning a wide range of transport conditions. Part I presents the development and validation (section 2) of a novel multi-frequency (wide-band) Acoustic Concentration and Velocity Profiler (ACVP), designed to measure co-located velocity and particle concentration profiles at high spatio-temporal resolution. This instrument extends the spectral bandwidth of the ACVP technology originally proposed by Hurther et al. (2011) and Fromant et al. (2018). It combines ADVP and ABS technologies for turbulence-resolved velocity and particle concentration profiling across bedload and suspension layers. Its application to heavy particle-laden flows in the LEGI tilting flume is presented in section 3, using highly inertial 3 mm PMMA particles. The experimental protocol proposed by Guta et al. (2022) will be applied. Narrow and wide-band ACVP measurements will be compared to evaluate mixture-based and two- phase fluid–particle velocity estimates. Part II, presented separately by Reymond et al. (2026), applies the single- and multi-frequency ACVP technologies to new sand-transport experiments in the EPFL tilting flume under energetic open -channel flow conditions. Preliminary comparisons of mean velocity, turbulence, and sediment fluxes between light -weight particle and sand-laden flows are aimed on the longer term, with particular attention given to bedload-layer effects on the dynamics of the upper turbulent suspension layer, as previously identified by Revil-Baudard et al. (2015, 2016) and Guta et al. (2022, 2024).

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.238

Year: 2026