Scaling relationships between bed load volumes, transport distances, and stream power in steep mountain channels

Abstract

Bed load transport during storm events is both an agent of geomorphic change and a significant natural hazard in mountain regions. Thus, predicting bed load transport is a central challenge in fluvial geomorphology and natural hazard risk assessment. Bed load transport during storm events depends on the width and depth of bed scour, as well as the transport distances of individual sediment grains. We traced individual gravels in two steep mountain streams, the Erlenbach (Switzerland) and Rio Cordon (Italy), using magnetic and radio frequency identification tags, and measured their bed load transport rates using calibrated geophone bed load sensors in the Erlenbach and a bed load trap in the Rio Cordon. Tracer transport distances and bed load volumes exhibited approximate power law scaling with both the peak stream power and the cumulative stream energy of individual hydrologic events. Bed load volumes scaled much more steeply with peak stream power and cumulative stream energy than tracer transport distances did, and bed load volumes scaled as roughly the third power of transport distances. These observations imply that large bed load transport events become large primarily by scouring the bed deeper and wider, and only secondarily by transporting the mobilized sediment farther. Using the sediment continuity equation, we can estimate the mean effective thickness of the actively transported layer, averaged over the entire channel width and the duration of individual flow events. This active layer thickness also followed approximate power law scaling with peak stream power and cumulative stream energy and ranged up to 0.57 m in the Erlenbach, broadly consistent with independent measurements.

The role of log jams and exceptional flood events in mobilizing coarse particulate organic matter in a steep headwater stream

“…The overall average recovery rate of tracers during all six surveys amounted to 34 % with the rates of the individual surveys varying between 29 and 45 %. These values are similar to the rates observed in a study of bedload motion at the same site also using RFID equipment (Schneider et al, 2010(Schneider et al, , 2014. The tracer logs preferably deposited in log jams (Fig.…”

“…2) were tagged with radio frequency identification (RFID) transponders, a technique that has successfully been employed to monitor bedload (Lamarre et al, 2005;Schneider et al, 2010Schneider et al, , 2014 and woody debris (MacVicar et al, 2009;Schenk et al, 2013;Ravazzolo et al, 2015). The RFID glass transponders we used were 3.12 cm long, 0.38 cm in diameter, emitting at 134.2 kHz frequency, and were glued into holes drilled into the tracer logs.…”

Bedload transport controls bedrock erosion under sediment-starved conditions

“…There, the relative importance of the four sediment effects presumably is different from the measurement site, and the threshold of bedload motion is higher (cf. Schneider et al, 2014). Since we focus on the chute channel, it would not be plausible to use a threshold of motion from the alluvial section.…”

Assessing the Performance of In-Stream Restoration Projects Using Radio Frequency Identification (RFID) Transponders

“…For instance, a number of studies in mixed-gravel beds have demonstrated the prevalence of partial mobility [37][38][39][40], and characterized the relation between particle size and travel distance [41][42][43]. Tracking methods using Radio Frequency Identification (RFID) transponders have become common in the research community due to their advantages over other tracking technologies in terms of individualized particle displacement information, low cost, battery-free nature and robust design [44][45][46][47][48][49][50][51]. Sediment tracking has been used to assess some restoration projects [52][53][54] but its potential for testable hypotheses to assess restoration outcomes has yet to be fully realized.…”