Form and stability of step‐pool channels: Research progress

[1] Research examining the hydraulics, morphology, and stability of step-pool mountain streams has blossomed in the last decade, resulting in more than a dozen dissertations. These, along with other research projects, have transformed our understanding of step-pool channels. Contributions have been made toward understanding depositional step formation and destruction, scour downstream of steps, step-pool hydraulics, and the effect of sediment transport on step stability. We propose that depositional steps exist in a jammed state whereby the boulders are structurally arranged within the channel and thereby stabilize it. Once a step has formed, a scour pool with a characteristic length and depth develops downstream, creating a zone where additional steps are unlikely to occur. Downstream of the scour hole, steps are more likely to occur as the high energy associated with the plunge pool has dissipated. Data suggest that the presence of cobbles or boulders limits pool scour as well as the degree to which well-defined, channel-spanning step-pools form. We propose a state-space for step-pools in which conditions for a step to form include (1) the ratio between width and boulder diameter (the jamming ratio), (2) the ratio between applied shear stress and the stress needed to mobilize the bed (relative Shields number), and (3) the ratio between bed material supply and discharge (bed sediment concentration). Available data suggest this model is plausible. Emerging critical research questions are discussed.

[1]  F. Swanson,et al.  Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon , 1990 .

[2]  B. C. Mcdonald,et al.  An experimental flume study on the formation of transverse ribs , 1978 .

[3]  V Ferro,et al.  Scour on Alluvial Bed Downstream of Grade-Control Structures , 2004 .

[4]  Bao De-Song,et al.  Critical phenomenon of granular flow on a conveyor belt. , 2003, Physical review. E, Statistical, nonlinear, and soft matter physics.

[5]  D. Montgomery,et al.  Channel-reach morphology in mountain drainage basins , 1997 .

[6]  Roberto Gaudio,et al.  Morphological effects of bed sills in degrading rivers , 2000 .

[7]  Luis A. Giménez-Curto,et al.  Highest natural bed forms , 2003 .

[8]  Tamotsu Takahashi,et al.  Mechanical Characteristics of Debris Flow , 1978 .

[9]  R. Kellerhals.  RUNOFF ROUTING THROUGH STEEP NATURAL CHANNELS , 1970 .

[10]  M. Church,et al.  Channel morphology, gradient profiles and bed stresses during flood in a step-pool channel , 2001 .

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

[12]  Ferro,et al.  Fenomeni di erosione localizzata a valle di opere trasversali: integrazioni tra indagini di campo e di laboratorio , 2005 .

[13]  P. Julien,et al.  SCOUR DOWNSTREAM OF GRADE-CONTROL STRUCTURES , 1991 .

[14]  Mario Aristide Lenzi,et al.  Interference processes on scouring at bed sills , 2003 .

[15]  Conditions for geometric similarity of coarse stream-bed roughness , 1987 .

[16]  Mario Aristide Lenzi,et al.  Local scouring at grade‐control structures in alluvial mountain rivers , 2003 .

[17]  P. Mason,et al.  Free jet scour below dams and flip buckets , 1985 .

[18]  M. Church,et al.  Experiments on surface structure and partial sediment transport on a gravel bed , 2000 .

[19]  André Robert,et al.  Boundary roughness in coarse-grained channels , 1990 .

[20]  Peter J. Mason.  Effects of Air Entrainment on Plunge Pool Scour , 1989 .

[21]  Shinji Egashira,et al.  Flow resistance and sediment transportation in streams with step-pool bed morphology , 1991 .

[22]  A. Chin.  Step pools in stream channels , 1989 .

[23]  J. Warburton.  Observations of Bed Load Transport and Channel Bed Changes in a Proglacial Mountain Stream , 1992 .

[24]  M. Cates,et al.  Jamming, Force Chains, and Fragile Matter , 1998, cond-mat/9803197.

[25]  A simplified cascade model for transverse stone-ribs in gravelly streams , 1983, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[26]  Pierre Y. Julien,et al.  Mechanics of jet scour downstream of a headcut , 1993 .

[27]  E. Wohl,et al.  Toward a theory for step pools in stream channels , 2005 .

[28]  N. Rajaratnam,et al.  Submerged flow regimes of rectangular sharp-crested weirs , 1996 .

[29]  J. Aberle,et al.  The influence of roughness structure on flow resistance on steep slopes , 2003 .

[30]  Andrea Marion,et al.  Analysis of small‐scale gravel bed topography during armoring , 2003 .

[31]  M. A. Lenzi.  Displacement and transport of marked pebbles, cobbles and boulders during floods in a steep mountain stream , 2004 .

[32]  E. Wohl,et al.  Controls on Bedload Movement in a Subalpine Stream of the Colorado Rocky Mountains, U.S.A. , 1994 .

[33]  N. M. Aziz,et al.  Sediment transport on steep slopes , 1986 .

[34]  P. Wilcock,et al.  Characteristic dimensions of the step‐pool bed configuration: An experimental study , 2005 .

[35]  D. M. Thompson,et al.  Velocity characteristics along a small step–pool channel , 2000 .

[36]  Luca Solari,et al.  Influence of macro-roughness arrangement on flow resistance , 2004 .

[37]  Joseph F. Atkinson,et al.  Step-Pool Streams: An Adjustment to Maximum Flow Resistance , 1995 .

[38]  R. Ferguson,et al.  Velocity and flow resistance in step-pool streams , 2002 .

[39]  P. J. Whiting,et al.  Alluvial architecture in headwater streams with special emphasis on step-pool topography , 2000 .

[40]  M. E. Cates,et al.  Jamming and stress propagation in particulate matter , 1999 .

[41]  William S. Platts,et al.  MORPHOLOGICAL FEATURES OF SMALL STREAMS: SIGNIFICANCE AND FUNCTION , 1986 .

[42]  André Robert,et al.  Statistical properties of sediment bed profiles in alluvial channels , 1988 .

[43]  P. Komar,et al.  Applications of grain-pivoting and sliding analyses to selective entrapment of gravel and to flow-competence evaluations , 1988 .

[44]  Luis A. Giménez-Curto,et al.  Oscillating turbulent flow over very rough surfaces , 1996 .

[45]  I. Banerjee,et al.  Sediments and Bed Forms on a Braided Outwash Plain , 1971 .

[46]  A. Chin.  The morphologic structure of step–pools in mountain streams , 1999 .

[47]  E. Wohl,et al.  Channel bed-steps along Nahal Yael, Negev desert, Israel , 1994 .

[48]  Mario Aristide Lenzi,et al.  Effect of sill spacing and sediment size grading on scouring at grade‐control structures , 2004 .

[49]  E. J. Hickin,et al.  Step-pool and cascade morphology, Mosquito Creek, British Columbia: a test of four analytical techniques , 2002 .

[50]  P. Burlando,et al.  Spatial organization in the step‐pool structure of a steep mountain stream (Vogelbach, Switzerland) , 2006 .

[51]  M. Church,et al.  Quantifying variability in stream channel morphology , 2003 .

[52]  Vladimir Nikora,et al.  On gravel‐bed roughness characterization , 1998 .

[53]  E. Wohl,et al.  Field measurements of three-dimensional hydraulics in a step-pool channel , 2007 .

[54]  Kazuyoshi Hasegawa,et al.  ROLES OF HETEROGENEOUS PROPERTY OF BED MATERIALS FOR THE FORMATION OF STEP-POOL SYSTEMS IN MOUNTAIN STREAMS , 1998 .

[55]  M. A. Lenzi.  Step–pool evolution in the Rio Cordon, northeastern Italy , 2001 .

[56]  Peter R. Wilcock,et al.  Reply to comment by Luis A. Giménez-Curto and Miguel A. Corniero Lera on “Characteristic dimensions of the step-pool bed configuration: An experimental study” , 2006 .

[57]  Kazuo Ashida,et al.  Sediment Yield and Transport on a Mountainous Small Watershed , 1976 .

[58]  F. Comiti,et al.  Effective discharge for sediment transport in a mountain river: Computational approaches and geomorphic effectiveness , 2006 .

[59]  Mario Aristide Lenzi,et al.  Dimensions of standing waves at steps in mountain rivers , 2006 .

[60]  E. Wohl,et al.  Characteristics of log and clast bed-steps in step-pool streams of northwestern Montana, USA , 1997 .

[61]  E. Wohl,et al.  Flow resistance dynamics in step‐pool channels: 2. Partitioning between grain, spill, and woody debris resistance , 2006 .

[62]  F. Comiti,et al.  Morphological effects of local scouring in step–pool streams , 2005 .

[63]  Michael Church,et al.  Stabilizing self‐organized structures in gravel‐bed stream channels: Field and experimental observations , 1998 .

[64]  J. Whittaker,et al.  Origin of step-pool systems in mountain streams , 1982 .

[65]  S. Bennett.  Effect of slope on the growth and migration of headcuts in rills , 1999 .

[66]  P. K. Mohanty,et al.  Flume Studies of Flow in Steep, Rough Channels , 1960 .

[67]  Mario Aristide Lenzi,et al.  Local scouring and morphological adjustments in steep channels with check-dam sequences , 2003 .

[68]  Vincenzo D'Agostino,et al.  Bedload transport in the instrumented catchment of the Rio Cordon , 1999 .

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

[70]  E. Wohl,et al.  Large woody debris and flow resistance in step-pool channels, Cascade Range, Washington , 2003 .

[71]  G. Grant.  Hydraulics and sediment transport dynamics controlling step-pool formation in high gradient streams: A flume experiment , 1994 .

[72]  A. Robert.  Fractal properties of simulated bed profiles in coarse-grained channels , 1991 .

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

[74]  P. Wilcock,et al.  Experimental study of incipient motion in mixed‐size sediment , 1988 .

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

[76]  Dieter Rickenmann,et al.  Bedload transport capacity of slurry flows at steep slopes , 1990 .

[77]  M. Church.  Geomorphic thresholds in riverine landscapes , 2002 .

[78]  Gordon E. Grant,et al.  Critical flow constrains flow hydraulics in mobile‐bed streams: A new hypothesis , 1997 .

[79]  G. Pasternack,et al.  TDR measurements of hydraulic jump aeration in the South Fork of the American River, California , 2002 .

[80]  Nallamuthu Rajaratnam,et al.  Impinging jet and surface flow regimes at drop , 1998 .

[81]  Steven R. Abt,et al.  Drop Height Influence on Outlet Scour , 1994 .