Relative velocities of discharge and sediment waves for the River Severn, UK

Abstract

It is generally accepted that the celerity of a discharge wave exceeds that of a floodwave. The discharge wave is the initial wavefront (shown by an increase in stage at a particular site), whereas the floodwave refers to the body of water moving downstream. Yet, few studies have investigated the varying relationship between discharge and suspended sediment concentration as floods propagate downstream. This paper examines the relative velocities of the discharge and sediment waves for natural flood events on the River Severn, UK. Four monitoring stations were established within the upper 35 km reach of the River Severn (drainage basin area 380 km 2 ). Discharge was monitored using fixed structures, and suspended sediment concentrations were monitored at similar locations using Partech IR40C turbidity meters. Results showed discharge wave celerity increased with flood magnitude, but relationships were more complex for sediment wave celerity. Sediment wave celerity was greater than discharge wave celerity, and is attributed to the dominant source of sediment, which is most probably bank erosion. Les vitesses relatives des ondes d'écoulement d'eau et de sédiment de la Severn (Royaume-Uni)Résumé On admet généralement que la vitesse d'une onde d'écoulement est supérieure à celle d'une onde de crue. Cependant, peu d'études ont examiné la relation variable entre l'écoulement de l'eau et la concentration des matières en suspension lorsqu'une onde de crue se propage vers l'aval. Cet article étudie les vitesses relatives des ondes d'écoulement et de transport de sédiments pour des crues naturelles de la Severn (Royaume-Uni). On a mis en place quatre stations de mesure sur les 35 km du bief supérieur de la Severn (la surface du bassin versant étant de 380 km 2 ). On a mesuré le débit grâce à des installations fixes, et on a mesuré les concentrations des matières en suspension aux mêmes lieux à l'aide de compteurs de turbidité Partech IR40C. Les résultats ont montré que la vitesse de l'onde augmentait avec l'intensité de la crue, mais les relations étaient plus complexes en ce qui concerne la vitesse des ondes de sédiments. La vitesse des ondes de sédiments est plus grande que la vitesse des ondes d'écoulement, ce qui a été attribué à l'origine principale des sédiments qui est, selon toute probabilité, l'érosion des berges.

Hydrological and sediment transport dynamics of flushing flows: implications for management in large Mediterranean Rivers

“…Such high suspended sediment transport capacity is seen as a direct consequence of the flashiness of the hydrograph that optimize the effectiveness of the flushing flow by washing out fine sediments from riverbed, macrophytes and channel banks. Similar hypotheses and observations were reported by Bull (1997). The high suspended sediment transport capacity may play an important role in informing future management practices for sediment supply to the lowermost part of the river and its delta.…”

Secular Sediment Waves, Channel Bed Waves, and Legacy Sediment

“…The history of the sediment wave concept is reviewed by revisiting Gilbert’s (1917) type locale and a distinction between sediment and bed waves is made. The fluvial features and processes described here are not the same as marine bedforms described as sediment waves (Wynn and Stow 2002) or changes in sediment concentrations observed during a storm (Bull 1997).…”

The Fine‐Sediment Cascade

“…Anticlockwise or negative hysteresis occurs less frequently and has been associated with cases where sediment sources are distant from the point of measurement (Heidel, 1956) or where sediment is derived from bank collapse following the flood peak (Sarma, 1986;Ashbridge, 1995) or mobilized from the bed following biofilm break-up (Lawler et al, 2006). For larger catchments, other factors need to be considered such as the downstream propagation of the flood wave (Petts et al, 1985;Bull, 1997), the timing of water and sediment inputs from tributary streams (Smith et al, 2003a), size of temporary storage within the river channel (Asselman, 1999) and the relative velocity of the water and the sediment.…”