Critical specific stream power in gravel-bed rivers

Abstract

Experiments with marked pebbles were carried out on different sized rivers of the Belgian Ardenne (catchment areas varying from less than 1 km 2 to 2700 km 2 ). Specific stream power required to cause bedload movement was evaluated and critical values were obtained. Three types of relationship between critical specific stream power (x 0 ) and grain size (D) were established. The values for x 0 in the largest river (the Ourthe) were the lowest and were close to the values obtained for mountainous rivers carrying large boulders. In medium sized rivers (catchment area between 40 and 500 km 2 ), the critical unit stream power was higher. It is likely that it is due to the bedform's greater resistance. This resistance would use up some of the energy that can cause movement and transport of bedload. The amount of resistance of the bedform can be expressed as bedform shear stress (sW), determined by the relationship between grain shear stress (sV-that determines movement and transport of the bedload) and the total shear stress (s). This ratio varies between 0.4 and 0.5 in the medium sized rivers, compared to 0.7 in the Ourthe. In headwater streams (less than 20 km 2 ), there is greater loss of energy due to bedform resistance (sV/sb0.3). Critical specific stream power is higher in this third type of river than in the other two. D

Understanding the influence of slope on the threshold of coarse grain motion: Revisiting critical stream power

“…The empirical relationships collected by Petit et al (2005) ) where the velocity required to entrain a 223 particle to the power of 6 is linearly related to the volume of that sediment particle (Vanoni, 1975). Based on 224 …”

“…The first, and perhaps most significant, is that it is too complex for practical application given that 203 it requires the flow depth at the threshold of motion (Petit et al, 2005). This requires not only knowledge of 204 local flow properties, but also application of an iterative procedure to determine the critical flow depth in 205 question.…”

“…Partly as a result of this limitation, Petit et al (2005) set out to determine a relationship for the stream power 209 per unit bed area required to initiate bed-load movement in three types of rivers in the Belgian Ardenne 210 region. The river types were determined based on an arbitrary classification into large (catchment area > 500 211 km 2 ), medium (40 km 2 < catchment area < 500 km 2 ), and small/headwater streams (catchment area < 40 212 km 2 ).…”

Residual Doses in Recent Alluvial Sediments From the Ardenne (S Belgium)

“…They have quite a marked slope (varying from 0.001 m/m for larger rivers to 0.02 m/m for headwater streams), and generally develop meanders in narrow floodplains. The specific stream power of these rivers, for the bankfull discharge, is comprised between 25 and 150 W/m² (Petit et al, 2005). Their bedload consists mainly of phyllites, quartzites, schists and sandstones from the Cambrian and Eodevonian periods.…”

Long-term bedload mobility in gravel-bed rivers using iron slag as a tracer

“…The size and travel distance of mobilized grains can be estimated using painted pebbles (Leopold et al, 1966;Billi, 1988;Petit et al, 2005a), tracers containing iron or magnets (Hassan, 1990;Schmidt and Ergenzinger, 1992;Gintz et al, 1996;Ferguson et al, 2002), PIT-tag (Lamarre et al, 2005;Rollet et al, 2008) or active (radio) tracers (Ergenzinger et al, 1989;Busskamp and Hasholt, 1996;MacNamara and Borden, 2004). These methods evaluate bedload mobility over a relatively short timescale.…”