Abstract
Abstract. Hydromorphodynamic models are powerful tools for predicting the potential mobilization and transport of sediment in river ecosystems. Recent studies have shown that they are able to predict suspended sediment matter concentration in small river systems satisfactorily. However, hydro-sedimentary modelling exercises often neglect suspended sediment properties (e.g. sediment densities and grain-size distribution), which are known to directly control sediment dynamics in the water column during flood events. The main objective of this study is to assess whether a better representation of such properties leads to an improved performance in the model. The modelling approach utilizes a fully coupled hydromorphodynamic model based on TELEMAC-3D (v7p1) and an enhanced version of the sediment transport module SISYPHE (based on v7p1), which allows for a refined sediment representation (i.e. 10-class sediment mixtures instead of 2-class mixtures and distributed sediment density instead of uniform). The proposed developments of the SISYPHE model enable us to evaluate and discuss the added value of sediment representation refinement for improving sediment transport and riverbed evolution predictions. To this end, we used several model set-ups to evaluate the influence of sediment grain-size distribution, sediment density, and suspended sediment concentration at the upstream boundary on model predictions. As a test case, we simulated a flood event in a small-scale river, the Orne river in north-eastern France. Depending on the model set-up, the results show substantial discrepancies in terms of simulated bathymetry evolutions. Moreover, the model based on an enhanced configuration of the sediment grain-size distribution (10 classes of particle sizes) and with distinct densities per class outperforms the standard SISYPHE configuration, with only two sediment grain-size classes, in terms of simulated suspended sediment concentration.
Highlights
In the last 2 centuries, many areas have undergone rather fast demographic, industrial and urban development
The modelling approach utilizes a fully coupled hydromorphodynamic model based on TELEMAC-3D (v7p1) and an enhanced version of the sediment transport module SISYPHE, which allows for a refined sediment representation (i.e. 10-class sediment mixtures instead of 2-class mixtures and distributed sediment density instead of uniform)
This study evaluates the influence of the sediment grain-size distribution, the sediment density, and the upstream suspended sediment concentration (SSC) representation in sediment transport and morphodynamic modelling
Summary
In the last 2 centuries, many areas have undergone rather fast demographic, industrial and urban development This intense land occupancy has affected the quality of surface waters, which became the receptacle of anthropogenic effluents from various origins (Whitman, 1998; Heise and Förstner, 2006, 2007; Grabowski et al, 2011). As a consequence of these past effluent emissions, riverbed sediments often remain contaminated, part of the settled material has been dredged and removed (Kanbar et al, 2017). The remobilization of these riverbed sediments during flood events can subsequently affect water quality and contaminate floodplains (Carter et al, 2006; Hissler and Probst, 2006) and requires. There is, a clear need to predict the potential resuspension and transport of sediment in these heavily polluted river systems
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