Assessment of suspended sediment transport in four alpine watersheds (France): influence of the climatic regime

Abstract

International audienceHigh-frequency water discharge and suspended sediment concentration (SSC) databases were collected for 3 years on four contrasted watersheds: the Asse and the Bléone (two Mediterranean rainfall regime watersheds) and the Romanche and the Ferrand (two rainfall-snowmelt regime watersheds). SSCs were calculated from turbidity recordings (1-h time step), converted into SSC values. The rating curve was calculated by means of simultaneous SSC measurement taken by water sampling and turbidity recording. Violent storms during springtime and autumn were responsible for suspended sediment transport on the Asse and the Bléone rivers. On the Ferrand and the Romanche, a large share of suspended sediment transport was also caused by local storms, but 30% of annual fluxes results from snowmelt or icemelt which occurred from April to October. On each watershed, SSC up to 50 g l-1 were observed. Annual specific fluxes ranged from 450 to 800 t km-2 year-1 and 40-80% of annual suspended sediment fluxes occurred within 2% of the time. These general indicators clearly demonstrate the intensity of suspended sediment transport on these types of watersheds. Suspended sediment fluxes proved to be highly variable at the annual scale (inter-annual variability of specific fluxes) as well as at the event scale (through a hysteresis loop in the SSC/Q relationship) on these watersheds. In both cases, water discharge and precipitations were the main processes involved in suspended sediment production and transport. The temporal and spatial variability of hydro-meteorological processes on the watershed provides a better understanding of suspended sediment dynamics

Dominant mechanisms for the delivery of fine sediment and phosphorus to fluvial networks draining grassland dominated headwater catchments

“…The rapid response of SSC to hydrological forcing implies that the SS sources are readily accessible with the majority of SS being generated from areas proximal to the channel (Bača, 2008;Lefrançois et al, 2007;Rodríguez-Blanco et al, 2010). These sediment sources include: bed material (Arnborg et al, 1967;Bogen, 1980), bank material (Langlois et al, 2005;Seeger et al, 2004;Smith and Dragovich, 2009) and hydrologically connected areas close to the channel which respond rapidly at the onset of a storm (Mano et al, 2009;Reid et al, 2007). Factor analysis has illustrated that these event dynamics have no threshold of initiation and may occur across the full range of environmental conditions observed.…”

Suspended sediment behavior in a coastal dry-summer subtropical catchment: Effects of hydrologic preconditions

“…Sediment and water supply to the channel are controlled by the same major factors, namely precipitation distribution and intensity, basin structure (relief, substrate composition), and basin preconditions (moisture levels, vegetation states, disturbance states) (Wischmeier and Smith, 1978;Syvitski et al, 2000;Lana-Renault et al, 2007;Mano et al, 2009). Increased shear stress during floods can erode channel margins, scour away stabilizing structures such as vegetation, and activate landslide snouts adjacent to the channel in upper basin areas, all of which can lead to increased channel bank and hillslope sediment delivery (Kelsey, 1980;Benda and Dunne, 1997;Poesen and Hooke, 1997;Korup, 2012).…”

Assessment of intermediate fine sediment storage in a braided river reach (southern French Prealps)

“…These areas generally show very high suspended sediment yields (SSYs) (Milliman and Syvitski, 1992;Hicks et al, 2000;Lenzi et al, 2003;Mathys et al, 2003;Meybeck et al, 2003;Liebault et al, 2005;Mano et al, 2009) and therefore they govern the temporal variability of fine sediment delivery in lowland fluvial systems. In these areas, the main issues involve hydroelectricity production, problems with reservoir silting but also the quantity and quality of water resources.…”