Session D2: Solid transport and bed load

Tuesday 1st of july – 16:30

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16:30

Monitoring the post-flood hydrogeomorphological dynamics of two rivers in the Saguenay region (Quebec)

AUTHORS

GILLET Maxime, BOIVIN Maxime, BÉRUBÉ Johan, VIN DESLAURIERS Janie, BUFFIN-BÉLANGER Thomas

Canada

Short Abstract: The Saguenay rivers were severely affected by the flood of July 1996. The intense hydrological response to this event resulted in changes to the morphology and sediment dynamics of the region’s rivers. In response to these new conditions, massive bank riprap was constructed, with a strong effect on hydrogeomorphological processes (HGM). The objective of this study will therefore be to characterize HGM dynamics pre- and post-flood by studying two Saguenay rivers that have undergone massive riprap and more precisely by analyzing the lateral and vertical mobility of river trajectories.The results allow us to characterize the sediment dynamics of these two rivers over the two periods. They show the impact of these constructions, which severely restrict the lateral migration of the streams and thus reduce their sediment input. This reduction in sediment input is compensated for by river incision. However, although the processes are similar, their intensities vary greatly, with lower rates for the river with the highest rate of riprap. This is due to the high sediment input of certain tributaries, which limit the overall deficit and are therefore essential to protect. This study underlines the impact of riprap on river dynamics and promotes the need for detailed knowledge of the processes involved in order to maximize restoration operations.

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16:50

Sediment transport in a Mediterranean mountain stream catchment: 7 years’ monitoring feedback and sediment fluxes modelling in climate change context (Roya River, Maritime Alps, France)

AUTHORS

CHAPUIS Margot, ADNÈS Cyriel, LOMBARD Florent, FOX Dennis

France

Short Abstract: As other rivers of the Mediterranean Riviera, the Roya is a characterized by hydrological extremes, high sediment fluxes and dense valley floor land use. The research undertaken in the catchment aimed at characterizing and quantifying sediment fluxes at catchment scale, to define a prospective modelling of sediment fluxes in climate change context. Field monitoring since 2016 notably included RFID tracking and passive seismic monitoring. A 1000 years-return period flood that occurred on 2020/10/02 was a unique opportunity to analyze the system trajectory after such an intense event. The average and maximum distances of sediment transport in relation with the duration of the study and the excess unit stream power confirm that the Roya is particularly dynamic. The post-flood trajectory suggests increased mobility but will be maintained only with sufficient hydrology in the next years. This extreme event enables to analyze sediment fluxes at catchment scale in climate change context while questioning the resilience rhythm of the system.

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17:10

Modelling sediment transport at network scale and implications for river management: the case of the Po River (Italy)

AUTHORS

DOOLAEGHE Diane, BOZZOLAN Elisa, SHRESTHA Sahansila, CECCHETTO Martina, SURIAN Nicola, BRENNA Andrea, BIZZI Simone

Italy

Short Abstract: With about 17 million inhabitants, the Po Plain hosts one of the most human-impacted rivers in Europe. Given the large population, it is crucial to understand and plan its trajectory, in terms of sediment fluxes and morphological changes. Information on sediment transport is very scarce and the last survey at the network-scale dates back to 2005-2006. A new sediment management plan is ongoing, but data on river bathymetry and sediment transport fluxes remain limited. In recent years, one of the largest restoration projects ever proposed in Italy was launched on the Po River, aiming to reopen over 15 secondary channels along its main stem. In this context, a better understanding of sediment dynamics across the Po River network is needed for a more effective management. This can be supported by the use of network-scale numerical models to make better-informed decisions. The present study applies the DCASCADE model to the Po River. We estimate sediment fluxes, budgets, and reach connectivity, and evaluate the sensitivity of uncertain model parameters. Despite lacking data for in-depth validation, the simulated fluxes are consistent with the last estimate carried out in 2005-2006. We further discuss plans for better validating the model, e.g. the use of recent morphological trajectories acquired from field measurements (DODs) and satellite images.

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17:30

Bedload and morphological active widths of gravel-bed rivers: variability among timescales

AUTHORS

BERNARD Thomas, PANDRIN Enrico, BERTOLDI Walter, CAPITO Lindsay, BIZZI Simone

Italy

Short Abstract: Active width, the portion of a river channel involved in sediment transport, is a crucial indicator of alluvial river dynamics, linking sediment transport to river morphological evolution. This study examines the temporal and spatial variability of bedload active width (BAW) and morphological active width (MAW) in gravel-bed rivers, by simulating different river types in the laboratory. The experiments simulated different river morphologies (braided, transitional, vagabond and alternating bar) with varying dimensionless stream powers. The results show that MAW systematically underestimates BAW by around 30%, whatever the river type, calling into question the assumptions for braided systems. Laboratory experiments also highlight the relationship between cumulative MAW and the time scale of analysis, in function of flood magnitude and duration. Analysis of morphological changes in the Tagliamento (Italy) and Sunwapta (Canada) rivers are consistent with laboratory observations, enabling quantitative analysis of morphological changes as a function of flood magnitude and duration. These perspectives improve understanding of sediment transport and river response to hydrological events, with implications for river management and flood risk assessment. Future work will explore non-stationary flow regimes and the effects of reduced confinement.

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17:50

The Rhone sediment observatory (OSR): a multi-partners platform for scientific and applied reserach on the Rhone river valley (France)

AUTHORS

RADAKOVITCH Olivier, COQUERY Marina, PIEGAY Hervé, MORANDI Bertrand

France

Short Abstract : The Rhône Sediment Observatory, created in 2009, involves an interdisciplinary research team (hydrology, hydraulics, geomorphology, geochemistry, geomatics, sedimentology) in strong interaction with river stakeholders. It aims to provide scientific knowledge for promoting a sustainable management of channel forms and sediment processes of this river, all along the main channel. A summary of the major findings after 16 years of research is proposed. They allowed to better characterize and explain the channel evolution of the last century, highlight aquatic and riparian habitat conditions, and assess channel sensitivity to changes. A network of monitoring stations is operating to continuously survey suspended particulate matter (SPM) concentrations, and to collect SPM samples for the analyses of their inorganic or organic contaminant contents. Fluxes of sediment and contaminants are calculated automatically from an open source database and an associated website accessible to scientific and stakeholders. Large events, including flash floods and sediment flushing, are also monitored at the river scale. Specific tools and protocols have been developed for monitoring sediment transfers, archiving data and sediment samples, and informing practitioners.