Temporal variability of suspended sediment sources in an alpine catchment combining river/rainfall monitoring and sediment fingerprinting

Abstract

Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905‐km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment. Sediment exports at the river catchment outlet (330 ± 100 t km‐2 yr‐1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra‐ and inter‐flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd.

Evaluating sampling efficiency when estimating sediment source contributions to suspended sediment in rivers by fingerprinting

“…On the other hand, event-based sampling also has important advantages in that they contain information on variation in sediment sources over time, both within and between events (Collins et al, 2001;Minella et al, 2008). This is especially true for small drainage basins, where sediment is emitted within events and there is interest in knowing how the emission of sediment varies within and between events (Collins et al, 2001;Minella et al, 2008;Navratil et al, 2012). In such catchments, it may be important to define the minimum number of samples needed to describe variability of the process adequately, whilst optimizing monitoring and laboratory costs.…”

Diel turbidity cycles in a headwater stream: evidence of nocturnal bioturbation?

“…These range from seasonal variations in SPM concentration driven by changing antecedent soil moisture conditions (Meybeck et al 1999;Halliday et al 2014) to hourly fluctuations driven by episodic high-energy, high-flow storm events which can mobilise large volumes of material through the initiation of rapid land-to-river surface sediment transfers (Navratil et al 2012;Cooper et al 2015). Intriguingly, recent research in North America and Europe has also found evidence of distinct diel cycles in fluvial SPM concentrations (Gillain 2005;Loperfido et al 2010).…”

A high space–time resolution dataset linking meteorological forcing and hydro-sedimentary response in a mesoscale Mediterranean catchment (Auzon) of the Ardèche region, France

“…At least five devices were available at the same time from 15 November 2011 (see Table A2 in Appendix A for the period of operation of the instruments). Moreover, a 2-D video disdrometer (2-D VD) was deployed at Le Pradel (south of the Gazel catchment) in autumn 2012 and 2013 for an inter-comparison of measurements (Raupach and Berne, 2015). All Parsivels except Saint-Etienne de Fontbellon and Pradel-Grainage are colocated with rain gauges from the network described in the next paragraph (Fig.…”

“…4). The correction technique described by Raupach and Berne (2015) using the 2-D VD as a reference disdrometer has been applied to Parsivel data, improving the consistency of recorded drop size distribution (DSD) moments.…”

“…Therefore, flash floods usually impact basins less than 1000 km 2 (Marchi et al, 2010). In mediumscale Mediterranean catchments, the control exerted by the amount of rainfall and its intensity and variability on the generation of runoff and the erosional processes operating at different scales is of major importance (Navratil et al, 2012;Marra et al, 2014;Tuset et al, 2016). Assisting stakeholders in implementing efficient soil conservation and river management measures implies understanding the processes and the factors that control surface runoff, developing modelling approaches able to provide reliable flow separations, localizing sediment sources and sinks, and predicting the space-time dynamics of sediment and associated contaminant within the catchment.…”