This paper synthesizes the literature on steppools, with particular reference to theory construction and explanatory models. The paper proceeds from a discussion of the fundamental aspects of steppools to a clarification of terminology.
Alluvial architecture in headwater streams with special emphasis on step-pool topography
Channel geometry ; Idaho ; Longitudinal section ; Mountain ; River bed ; Slope gradient ; Statistics ; Stream ; Topography ; United States of America
This study sought to develop a better understanding of channel types in mountainous watersheds with an emphasis placed on step-pool reaches. Specifically the AA. sought to determine the stream gradients associated with various types of self-formed
channel architecture (pool-riffle, plane bed, step-pool and cascades) and to develop relationships which could be used in predicting step-pool geometry and in understanding formative mechanisms.
Pool and riffle characteristics in relation to channel gradient
California ; Channel geometry ; Fluvial processes ; Geomorphometry ; Longitudinal section ; United States
The channel gradients, along three rivers in coastal northern California, discussed in this paper are higher than those often reported for channels with pool-riffle, rather sequences. However, the AA. have designated these as pool-riffle, than step
-pool, channels, because of the presence of a strong lateral flow component, and the lack of well-organized bed-steps spanning the entire channel width.
In this paper, natural step-pool geometry is compared with steep alluvial channels where grade-control structures such as check-dams and bed sills make the stream profile resemble a natural stepped stream. In order to test the hypothesis
lend support to an upstream-forced cascade model for step-pool formation, where the energy of falling jets controls the geometry of the pools, and is therefore regarded as the most important scaling-independent variable.
that natural pools are analogous to pools formed below grade-control works with respect to their dimensions, shape and formative dynamics, 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern Italian Alps. The results
body of literature applies what has been learned about steppools toward managing and restoring steepchannels.
This paper synthesizes the recent literature on steppools, with particular reference to theory construction and progress made over the past decade and a half. Four groups of contribution are identified. The first focuses on understanding
morphological relations in order to seek causal mechanisms. The second emphasizes processes that result from the step-pool configuration. The third is a group of integrative studies that seek broader explanations for steppools sequences. The fourth and growing
The morphologic structure of step-pools in mountain streams
California ; Channel geometry ; Discharge ; Fluvial dynamics ; Grain size distribution ; Longitudinal section ; Model ; Mountain ; River bed ; Stream ; United States of America
The purpose of this paper is to report a field-based investigation on the geometric structure of step-pools in the Santa Monica Mountain streams. The step-pool morphology is evaluated empirically in light of variations in a downstream direction
. To that end, a conceptual model of process-form linkages is proposed, whereby the step-pool morphology is produced by positive relationships between wavelength and discharge, and between height and particle size.
Characteristics of log and clast bed-steps in step-pool streams of northwestern Montana, USA
The role of log and clast steps was studied in 53 step-pool reaches in 32 streams in northwestern Montana. In each reach, 20 consecutive steps were sampled. No significant difference exists between clast and log steps with regard to step spacing
and step height. This suggested either that 1) woody debris is mobile in even the smallest channels in the study area, or 2) channel flows arrange clast steps around immobile woody debris. Calculations of flow resistance suggest that most steps serve
to maximize flow resistance. These results support the second hypothesis, that the height and spacing of clast steps are adjusted around immobile log steps to maintain consistent step characteristics.
, with discharge in step-poolchannels; to compare these findings with standard predictive equations using a roughness height; and to see how the parameter values which optimise the fit of appropriate resistance equations relate to measured bed properties.
The AA. present hydraulic measurements and calculations from 6 step-pool reaches of natural streams and from flume experiments dynamically similar to the prototypes. They aim to determine how rapidly flow resistance decreases, and velocity increases
Channel bed steps and pool shapes along Soda Creek, Three Sisters Wilderness, Oregon
Field study of bedrock step-pool systems along the upper reaches of Soda Creek shows strong correlation between several form variables (shape) and channel slope. Although step height and step length showed no regular spacing and variable correlation
with channel slope, length to height ratios demonstrated strong negative correlations. Correlations between step height to length ratios and channel slope varied between 3 lithologies (basalt, andesite, dacite). The frequency of pool shape classes did not vary
Step-pool formation models and associated step spacing
Multi-scale characterization and evolution of channel forms in gravel-bed rivers
Channel geometry ; Experimentation ; Gravel ; Longitudinal section ; Model ; River bed ; Stream
This research presents flume studies designed to identify the processes responsible for step-pool formation. The experimental design includes a broad range of flow rates and sediment transport rates to address questions of how the step-pool bedform
develops and the channel conditions most likely to produce step sequences. The experimental design included flow rates that created active transport and deposition of all sediment sizes, including the step-forming grains. This research evaluates the pre
In this paper the results of the flume study are presented that focus on bed morphology and the generation of step-poolchannels. In contrat to a number of other flume studies, the generation and configuration of steps and pools was studied
formation and the analysis of planform step types depending on stream power both suggest that steepchannels have a potential for self-stabilization by modifying the step-pool structure towards a geometry that provides maximum flow resistance and maximum bed
did not contribute to the generation of the step structures. However, the data of the presented study fits well into the region of antidune formation proposed by Kennedy for sand-bed rivers. The considerations of the Kennedy region of antidune
Velocity characteristics along a small step-poolchannel
Channel geometry ; Colorado ; Discharge ; Fluvial hydrology ; Longitudinal section ; Mountain ; River bed ; Stream ; Stream flow ; Turbulence ; United States of America
This paper summarizes measurements of velocity along 3 reaches of a small mountain channel with step-pool bedforms. Data analyses focused on characteristics of velocity profiles, and on correlations between velocity characteristics and the potential
to be less effective energy dissipators than the wake-generated turbulence and form drag of step-pool bedforms.
control variables bedform type, reach gradient and flow depth. To test the hypothesis that velocity characteristics are related to channel bedform types, ANOVA and ANCOVA tests were performed. The bed-generated turbulence and skin friction of runs appear
The AA. apply both spectral analysis and autoregressive integrated moving average (ARIMA) modeling, a parsimonious stochastic approach to 11 alluvial mountain step-pool streams for identifying their periodicities. They interpolate the original
procedure for identifying the periodicity of a step-pool sequence using spectral analysis with the differencing detrending method and multiple equal-space intervals is proposed. The identified periodicities might serve as an independent morphologic index
to infer hydraulic processes controlling the formation of the alluvial step-pools because they are significantly related to spill resistance of the alluvial step-pools.
Sediment routing hypothesis for pool-riffle maintenance
Bank erosion ; California ; Channel geometry ; Hydrodynamics ; Model ; Sediment load ; Sediment transport ; Spatial variation ; Step-poolchannel ; Stream ; Tracer ; United States of America
This paper provides evidence that sediment routing around pools is a key mechanism for pool-riffle maintenance in sinuous upland gravel-bed streams. A combination of clast tracing using passive integrated transponder (PIT) tagging and bedload traps
(positioned along the thalweg on the upstream riffle, pool entrance, pool exit and downstream riffle) are used to provide information on clast pathways and sediment sorting through a single pool-riffle unit. Computational fluid dynamics (CFD) is also used
to explore hydraulic variability and flow pathways. Clast tracing results provide a strong indication that clasts are not fed through pools, rather they are transported across point bar surfaces, or around bar edges. Spatial variations in bedload transport
were found throughout the pool-riffle unit. The pool entrance bedload trap was often found to be empty, when the others had filled, further supporting the notion that little or no sediment was fed into the pool. The pool exit slope trap would
Field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step-poolchannel
The aim was to develop a systematic methodology to rapidly survey, digitize and visualize bed and water surface topographies of 2 common types of natural jump regions (submerged and unsubmerged) in a bedrock step-poolchannel. In addition
the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels.
conditions are carried out and interpreted by means of a theoretical model. Finally, a criterion is obtained to estimate flow resistance developed by natural step-pool streams when a formative flow discharge occurs based on geometric quantities only.
The AA. investigate flow resistance developed by macro-roughness represented by pebbles positioned on a granular layer according to a regularly spaced stripe pattern on steep bed slopes. Flume experiments under various geometrical and hydraulic
The challenge of modeling pool–riffle morphologies in channels with different densities of large woody debris and boulders
Boulder ; Channel geometry ; Fluvial dynamics ; Habitat ; Longitudinal section ; Model ; New England ; Step-poolchannel ; Stream ; United States of America ; Woody debris
A Monte Carlo simulation approach and developmental computer model was created to predict pool formation, spacing and the percentage length covered by pools, riffles, scour holes and runs based on input data that include channel slope, width
that then controls local water-surface slopes, velocity patterns and the locations of pools and riffles. The spacing values of individual types and sizes of obstructions are modeled as log-normal distributions with separate distributions for each obstruction type
. Pools are assigned different probabilities of development depending on the obstruction type. The model accurately mimics some statistical attributes of pool spacing, and future versions of the model could be developed to improve overall predictive
The impact of exceptional events on erosion, bedload transport and channel stability in a step-poolchannel
times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step-pool morphology. The aim of this paper is to present observations of these exceptional events and discuss
Sediment transport in the Erlenbach, a small stream with step-pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return
the implications of boulder mobility on long-term channel stability.
The aim of this paper is to analyse data on transverse ribs, step-pools and riffle and pool sequences, measured by the authors on a few rivers in the Italian Alps and the northern Apennines. Open questions about the origin of these bedforms
in order to discriminate the fields of existence of the larger roughness transverse, cyclic elements of gravel bed rivers and to show that transverse ribs, step-pools and riffle and pool sequences are part of a coarse grained bedform continuum.
particle and channel width) is found as a relevant parameter in the development of the bedforms considered. The conditions and the interplays between the jamming factors and others parameters such as bedform wavelength and streambed gradient are considered
A revised velocity-reversal and sediment-sorting model for a high-gradient, pool-riffle stream
Carrying capacity ; Channel geometry ; Colorado ; Discharge ; Fluvial processes ; Grain size distribution ; Longitudinal section ; River bed ; Rocky Mountains ; Sediment transport ; Stream ; Stream flow ; Tracer ; United States of America
Sediment-sorting processes related to varying channel-bed morphology were investigated from April to November 1993 along a 1-km pool-riffle and step-pool reach of North Saint Vrain Creek, a small mountain stream in the Rocky Mountains of northern
Colorado. Measured cross-sectonal areas of flow and tracer particle deposition patterns were used to determine if water-surface slope and recirculating eddy-induced velocity reversals provide a viable pool-riffle sediment-sorting mechanism.