Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the bedload‐suspended load relationship

Abstract

Suspended load transport can strongly impact ecosystems, dam filling and water resources. However, contrary to bedload, the use of physically based predicting equations is very challenging because of the complexity of interactions between suspended load and the river system. Through the analysis of extensive data sets, we investigated extent to which one or several river bed or flow parameters could be used as a proxy for quantifying suspended fluxes in gravel bed rivers. For this purpose, we gathered in the literature nearly 2400 instantaneous field measurements collected in 56 gravel bed rivers. Among all standard dimensionless parameters tested, the strongest correlation was observed between the suspended sediment concentration and the dimensionless bedload rate. An empirical relation between these two parameters was calibrated. Used with a reach average bedload transport formula, the approach allowed to successfully reproduce suspended fluxes measured during major flood events in seven gravel bed alpine rivers, morphodynamically active and distant from hillslope sources. These results are discussed in light of the complexity of the processes potentially influencing suspended load in a mountainous context. The approach proposed in this paper will never replace direct field measurements, which can be considered the only confident method to assess sediment fluxes in alpine streams; however, it can increment existing panel tools that help river managers to estimate even rough but not unrealistic suspended fluxes when measurements are totally absent. © 2019 John Wiley & Sons, Ltd.

The Dynamics of Suspended Sediment in a Typical Alpine Alluvial River Reach: Insight From a Seasonal Survey

“…Cross sections were surveyed 4 times in the downstream reach (S1 to S4, dashed white lines). The top left panel shows the relation between sediment sources configuration (eroded area vs river bed area distribution along the channel path) and an hysteresis index (between the suspended sediment concentration (SSC) and the discharge at the event scale) for the Séveraisse and 10 other Alpine catchments presented in Misset, Recking, Navratil, et al (2019). Low values of the source configuration index indicate large river beds and distant eroded areas, while high values indicate close eroded areas and narrow river beds.…”

Using Continuous Turbidity and Seismic Measurements to Unravel Sediment Provenance and Interaction Between Suspended and Bedload Transport in an Alpine Catchment

“…The observed suspension‐gravel bed interactions are consistent with several flume and scarce field results. Previous studies show that fine particles infiltrate in the gravel matrix even for very low Rouse numbers and stay in the subsurface until the surface coarse bed particles are mobilized (Diplas, 1994; Frostick et al., 1984; Krishnappan & Engel, 2006), so that a relationship between suspended load and bedload is observed in gravel bedded streams (Meunier et al., 2006; Misset, Recking, Legout, Valsangkar, et al., 2019; Misset, Recking, Navratil, et al., 2019; Park & Hunt, 2017; Turowski et al., 2010). Also, in addition to the strong relationship between turbidity and seismicity, a weak relationship during the summer periods, when most high turbidity peaks occur, provides an indication of the origin of suspended sediment ( bed related vs. hillslope related ).…”

Interactions entre flux en suspension et lit d’une riviere alluviale alpine – cas de La Séveraisse

“…L'activation de différentes sources de sédiment devient alors un élément central qui, en plus de la capacité de transport de l'écoulement, contrôle les flux en suspension véritablement transportés. Ainsi, de précédentes études suggèrent que la mobilité des rivières à galets (et le relargage de sédiments fins associé) contrôle de manière significative la disponibilité des sédiments fins transportés en suspension (Meunier et al, 2006 ;Misset et al, 2021 ;Misset et al, 2019b ;Park and Hunt, 2017 ;Turowski et al, 2010). Cette hypothèse est cohérente avec les fortes interactions suspension/lit et les évolutions concomitantes des flux par suspension et par charriage observées sur la Séveraisse.…”

“…Cette hypothèse est cohérente avec les fortes interactions suspension/lit et les évolutions concomitantes des flux par suspension et par charriage observées sur la Séveraisse. Sur la base de cette réflexion, une relation entre charriage et suspension a été proposée par Misset et al (2019b). Cette relation qui caractérise l'apport en sédiments fins liés à la mobilisation du lit est comparée sur la Figure 5 à deux relations (Bagnold 1966 ;Celik et Rodi 1991) caractérisant la capacité de l'écoulement à maintenir une certaine concentration en suspension, pour la période de mesure de mai-juin 2018 (Figure 5).…”

“…Ainsi, de nouvelles approches de modélisation pourraient combiner les deux types d'équations. Il serait ainsi possible de « borner » en partie supérieure la relation suspension/débit par une équation déterminant la capacité de l'écoulement à maintenir en suspension (type Bagnold ou Celik et Rodi) et en partie inférieure par une relation caractérisant l'apport minimum des sources (type Misset et al 2019b). Ce genre d'approche permettrait d'établir des scénarios selon l'activation ou l'inactivation de différentes sources sédimentaires.…”