Internal structure of intense collisional bedload transport

Abstract

Intense bed load refers to a regime which is responsible of most of sediment transport in torrents and rivers during floods. Even if restricted to uniform steady conditions and well sorted particles, the liquid and solid phases interact in a rather complex way over the plane mobile bed. We focus on flow conditions where the sediment grains in the flow are supported by mutual contacts, primarily collisions, and not by the fluid turbulence. Nonetheless, the turbulent liquid stresses are important everywhere, but the top of the bed, and may not be neglected. Being particles and fluid reciprocally affecting at various scale, mechanical interpretations are challenging and not consolidated, yet. In this picture, it is clear that experimental evidences provide a fundamental, still lacking, piece of information.We contribute with new experiments in a tilting flume to face this need. Compared to previous laboratory tests, we apply various measuring techniques, getting to a robust validation of the acquired dataset. We exploited stereoscopic imaging techniques to capture the solid concentration and the three components of grain velocity, and extract the velocity fluctuations from the local mean values. Measured velocity distributions are independently checked by using an Ultrasonic Doppler Velocimetry technique.With all the needed quantities available, we exploited the constitutive relations based on the kinetic theory for granular flow, to highlight how the comparison between predictions and measurements works, deploying some accuracy deficiencies in the measurement and/or interpretation limits. Our results also address the attention to interfaces that separate layers affected by different rheological mechanisms. Along with pure experimental and theoretical aspects, we grasp the chance to use the data to check how the relations involving global quantities (discharges, friction factor, bed slope, flow depth), so common in hydraulic practice, work when the sediment transport is intense.

Modelling Intense Combined Load Transport in Open Channel

“…Our previous work was concerned with intense transport of contact load dominated by intergranular collisions. We built our experimental database of results for contact-load transport of lightweight sediments in a laboratory tilting flume [24][25][26] and used it to test constitutive relations of the classical kinetic theory and the extended kinetic theory at conditions typical for intense contact-load transport [25]. Selected constitutive relations based on the classical kinetic theory were employed in a collisional transport model for intense bed load in open-channel flow [27].…”

River, Coastal and Estuarine Morphodynamics Selected papers from the 10th anniversary of the RCEM Symposium

“…(), Matoušek et al . () and Porcile et al . () show how laboratory experiments can be used to unravel physical processes at quite different spatial and temporal scales and in different environments.…”

“…Matoušek et al . () explore experimentally the internal structure of intense collisional bedload transport, applying various measuring techniques (stereoscopic imaging techniques, ultrasonic Doppler velocimetry) to get a robust validation of the acquired dataset. Eventually, the collected data are used to assess how relations involving global quantities (discharge, friction factor, bed slope, flow depth), commonly used in hydraulic practice, perform in the presence of intense sediment transport rates.…”

“…The 17 collected contributions include four state-of-science papers concerning the most recent advances in computational morphodynamic modelling of coupled flow-bed-sediment systems (Shimizu et al, 2019), a critical analysis of existing data on vegetation-flow-sediment interactions obtained through both laboratory experiments and field campaigns (Tinoco et al, 2020), a review of existing moving-boundary theories of shorelines with two extensions to allow inclusion of firstorder effects of waves and tides (Voller et al, 2020), and an overall assessment of the role played by wave forcing on the hydro-morphodynamics in shallow nearshore areas and at river mouths (Brocchini, 2019). The other 13 papers cover different topics about morphodynamics, spanning multiple environments, tackling concepts and processes with the aid of refined theoretical and numerical tools (Redolfi et al, 2019;Tambroni et al, 2019), grounding the results on laboratory data (Finotello et al, 2019;Geng et al, 2019;Matoušek et al, 2019, Porcile et al, 2020 and field observations (Fogarin et al, 2019;Tommasini et al, 2019), and making use of interdisciplinary approaches (Calvani et al, 2019;Chen et al, 2019;Pivato et al, 2019;van de Vijsel et al, 2020) also to develop new conceptualizations (Schlömer et al, 2020).…”

“…The bar pattern emerging from numerical simulations is found to have consistent features with those observed in the field, suggesting 2020) show how laboratory experiments can be used to unravel physical processes at quite different spatial and temporal scales and in different environments. Matoušek et al (2019) explore experimentally the internal structure of intense collisional bedload transport, applying various measuring techniques (stereoscopic imaging techniques, ultrasonic Doppler velocimetry) to get a robust validation of the acquired dataset. Eventually, the collected data are used to assess how relations involving global quantities (discharge, friction factor, bed slope, flow depth), commonly used in hydraulic practice, perform in the presence of intense sediment transport rates.…”