Start and end of bedload transport in gravel‐bed streams

[1] The threshold of incipient bedload motion, expressed either as a critical force or as a critical water discharge, is a key parameter in bedload transport prediction. Measuring the threshold of motion is difficult, and reliable data from natural streams are rare. By recording the vibrations triggered by bedload particles when moving over a steel plate mounted in the channel bed, we determined the time at start and end of bedload transport in four streams, where discharge is continuously monitored. The threshold discharge scatters over approximately one order of magnitude for each stream, reinforcing previous observations that critical discharge is characterized by a distribution of values. We interpret a strong correlation between the discharge at the start of transport and the discharge at the end of transport of the previous event to reflect temporal changes in bed structure and consequent effects on the driving and resisting forces acting on the bed.

[1]  P. Molnar,et al.  The influence of landsliding on sediment supply and channel change in a steep mountain catchment , 2006 .

[2]  W. Dietrich,et al.  Sediment supply and the development of the coarse surface layer in gravel-bedded rivers , 1989, Nature.

[3]  Karl-Heinz Schmidt,et al.  FREQUENCY AND MAGNITUDE OF BEDLOAD TRANSPORT IN A MOUNTAIN RIVER , 1996 .

[4]  A. Badoux,et al.  The impact of exceptional events on erosion, bedload transport and channel stability in a step‐pool channel , 2009 .

[5]  Jens M. Turowski,et al.  Measuring the Statistics of Bedload Transport Using Indirect Sensors , 2010 .

[6]  Stuart N. Lane,et al.  The timing and magnitude of coarse sediment transport events within an upland, temperate gravel-bed river , 2007 .

[7]  J. S. Barton,et al.  Monitoring Coarse Bedload Transport with Passive Acoustic Instrumentation : A Field Study , 2010 .

[8]  J. Smith,et al.  Calculations of the critical shear stress for motion of uniform and heterogeneous sediments , 1987 .

[9]  W. Dietrich,et al.  A mechanistic model for river incision into bedrock by saltating bed load , 2004 .

[10]  H. Einstein,et al.  The Bed-Load Function for Sediment Transportation in Open Channel Flows , 1950 .

[11]  R. Marston.  Land, Life, and Environmental Change in Mountains , 2008 .

[12]  André Zimmermann,et al.  Form and stability of step‐pool channels: Research progress , 2007 .

[13]  R. Ferguson.  Critical discharge for entrainment of poorly sorted gravel , 1994 .

[14]  A. Badoux,et al.  One hundred years of mountain hydrology in Switzerland by the WSL , 2006 .

[15]  F. Schlunegger,et al.  Pleistocene/Holocene climate change, re‐establishment of fluvial drainage network and increase in relief in the Swiss Alps , 2003 .

[16]  P. Wilcock.  Flow competence: A criticism of a classic concept , 1992 .

[17]  Dieter Rickenmann,et al.  Comparison of bed load transport in torrents and gravel bed streams , 2001 .

[18]  P. Burlando,et al.  Analysis of changes in the step-pool morphology and channel profile of a steep mountain stream following a large flood , 2010 .

[19]  R. Luque.  Erosion And Transport Of Bed-Load Sediment , 1976 .

[20]  J. Bathurst.  Critical conditions for bed material movement in steep, boulder-bed streams , 1987 .

[21]  F. Comiti,et al.  When does bedload transport begin in steep boulder‐bed streams? , 2006 .

[22]  D. Lague,et al.  Distribution of erosion across bedrock channels , 2008 .

[23]  W. Dietrich,et al.  Is the critical Shields stress for incipient sediment motion dependent on channel‐bed slope? , 2007 .

[24]  P. Komar.  Selective grain entrainment by a current from a bed of mixed sizes; a reanalysis , 1987 .

[25]  D. Rickenmann,et al.  Continuous measurement of sediment transport in the Erlenbach stream using piezoelectric bedload impact sensors , 2007 .

[26]  A. Jensen,et al.  The functional relationship between peak spring floods and survival and growth of juvenile Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta) , 1999 .

[27]  D. Rickenmann,et al.  Calibration of piezoelectric bedload impact sensors in the Pitzbach mountain stream , 2008 .

[28]  Anthony J. Grass,et al.  Initial Instability of Fine Bed Sand , 1970 .

[29]  W. Dietrich,et al.  The variability of critical shear stress, friction angle, and grain protrusion in water-worked sediments , 1990 .

[30]  Jens M. Turowski,et al.  Tools and cover effects in bedload transport observations in the Pitzbach, Austria , 2009 .

[31]  Ellen Wohl,et al.  Linking Theory and Practice for Restoration of Step-Pool Streams , 2009, Environmental management.

[32]  G. Parker.  Surface-based bedload transport relation for gravel rivers , 1990 .

[33]  M. Church,et al.  An assessment of bed load sediment transport formulae for gravel bed rivers , 1989 .

[34]  D. Montgomery,et al.  A systematic analysis of eight decades of incipient motion studies, with special reference to gravel‐bedded rivers , 1997 .

[35]  P. Carling,et al.  An instrument to record sediment movement in bedrock channels , 2003 .

[36]  W. Dietrich,et al.  Friction angle measurements on a naturally formed gravel streambed: Implications for critical boundary shear stress , 1992 .

[37]  Luca Mao,et al.  Magnitude‐frequency analysis of bed load data in an Alpine boulder bed stream , 2004 .