Re-suspension of bed sediment in a small stream – results from two flushing experiments

Abstract

Streams draining small watersheds often exhibit multiple peaking sedigraphs associated with single peaking hydrographs. The process reasons of the multiple sediment peaks are not fully understood but they may be related to the activation of different sediment sources such as the streambed itself where deposited sediments from previous events may be available for resuspension. To understand resuspension of stream bed sediments at the reach scale we artificially flooded the small stream of the HOAL Petzenkirchen catchment in Austria by pumping sediment-free water into the stream. Two short floods were produced and flow, sediment and bromide concentrations were measured at three sites with high temporal resolution. Hydrologically, the two flood events were almost identical. The peak flows decreased from 57 to 7.9 L s⁻¹ and the flow volumes decreased from 17 to 11.3 m³ along the 590 m reach of the stream. However, a considerably smaller sediment load was resuspended and transported during the second flood due to depletion of stream bed sediments. The exception was the middle section of the stream where more sediment was transported during the second flood event which can be explained by differences between flow velocity and wave celerity and the resulting displacement of sediments within the stream. The results indicate that the first peak of the sedigraphs of natural events in this stream is indeed caused by the resuspension of streambed sediments, accounting for up to six percent of the total sediment load depending on total flow volume

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

“…The processes producing A8 events are difficult to decipher, although the enhanced SSC at low discharges on the rising limb of the hydrograph is likely a result of event water prominence and more specifically, within-channel sediment sources that are readily mobilised during the initial stages of the event (Eder et al, 2014). Such event characteristics…”

“…are likely a result of rapid remobilisation of material deposited during the recession period of the previous event (Bull, 1997;Eder et al, 2014). Factor analysis has indicated that the occurrence of these events at Stations A and B is preceded by a combination of fluvial quiescence and relatively high air temperatures.…”

“…Small scale experiments, in which the pollutant transport processes are controlled, have successfully produced the expected hysteresis dynamics, offering support for this indirect approach (e.g. Chanat et al, 2002;Eder et al, 2014). Analysis of the process dynamics of multiple contaminants using this hysteresis framework enables commonalities in transport systems to be assessed, and maximum information to be extracted about pollutant and catchment response to hydrological events (e.g.…”

Identification of prevailing storm runoff generation mechanisms in an intensively cultivated catchment

“…The artificial waves (uniform discharge of 40 l s -1 , volume of 16 m 3 ) were introduced into the channel 450 m upstream of the gauging station. The aim was to monitor the flood wave transformation and the sediment transport within the channel in a way similar to Eder et al (2014). On the basis of the results, it was concluded that the channel does contain sediment from previous erosion events that can be mobilized by even a slight increase of discharge.…”

“…On a recession limb of a hydrograph, the sediment concentration decreases. The reason is that mobile fine-grained particles are quickly flushed from the stream bed, and the flowing water does not have sufficient kinetic energy to carry heavier particles over a long distance (Dostál et al, 2013;Eder et al 2014). …”