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

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.