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Journal ArticleDOI

Review of step-pool hydrodynamics in mountain streams:

24 Jun 2019-Vol. 43, Iss: 5, pp 607-626

Abstract: Step-pools are one of the major types of bed morphology prevalent in mountain streams. They have a unique flow structure as compared to low-gradient streams, in terms of large boundary elements and...
Topics: Turbulence (52%), STREAMS (51%)
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Journal Article
Abstract: An experiment was conducted to study the maximum flow resistance of step pool streams and the morphology of the steps formed from clastic materials. The step pool formation was qualitatively simulated to analyze numerically the formation process. A flume 4.88 mm long and .15 m wide was used and flow velocity measurements were done by electronically timing passage of salt plume down the flume. Observations showed that the natural step pool streams arranged the morphology to maximize flow resistance.

9 citations

Journal ArticleDOI
Charles M. Shobe1, Charles M. Shobe2, Jens M. Turowski2, Ron Nativ3  +4 moreInstitutions (6)
Abstract: A landscape’s sediment grain size distribution is the product of, and an important influence on, earth surface processes and landscape evolution. Grains can be large enough that the motion of a single grain, infrequently mobile in size-selective transport systems, constitutes or triggers significant geomorphic change. We define these grains as boulders. Boulders affect landscape evolution; their dynamics and effects on landscape form have been the focus of substantial recent community effort. We review progress on five key questions related to how boulders influence the evolution of unglaciated, eroding landscapes: 1) What factors control boulder production on eroding hillslopes and the subsequent downslope evolution of the boulder size distribution? 2) How do boulders influence hillslope processes and long-term hillslope evolution? 3) How do boulders influence fluvial processes and river channel shape? 4) How do boulder-mantled channels and hillslopes interact to set the long-term form and evolution of boulder-influenced landscapes? 5) How do boulders contribute to geomorphic hazards, and how might improved understanding of boulder dynamics be used for geohazard mitigation? Boulders are produced on eroding hillslopes by landsliding, rockfall, and/or exhumation through the critical zone. On hillslopes dominated by local sediment transport, boulders affect hillslope soil production and transport processes such that the downslope boulder size distribution sets the form of steady-state hillslopes. Hillslopes dominated by nonlocal sediment transport are less likely to exhibit boulder controls on hillslope morphology as boulders are rapidly transported to the hillslope toe. Downslope transport delivers boulders to eroding rivers where the boulders act as large roughness elements that change flow hydraulics and the efficiency of erosion and sediment transport. Over longer timescales, river channels adjust their geometry to accommodate the boulders supplied from adjacent hillslopes such that rivers can erode at the baselevel fall rate given their boulder size distribution. The delivery of boulders from hillslopes to channels, paired with the channel response to boulder delivery, drives channel-hillslope feedbacks that affect the transient evolution and steady-state form of boulder-influenced landscapes. At the event scale, boulder dynamics in eroding landscapes represent a component of geomorphic hazards that can be mitigated with an improved understanding of the rates and processes associated with boulder production and mobility. Opportunities for future work primarily entail field-focused data collection across gradients in landscape boundary conditions (tectonics, climate, and lithology) with the goal of understanding boulder dynamics as one component of landscape self-organization.

5 citations

Journal ArticleDOI
31 Dec 2020-Water
Abstract: Three-dimensional numerical simulations were performed for different flow rates and various geometrical parameters of step-pools in steep open channels to gain insight into the occurrence of energy loss and its dependence on the flow structure. For a given channel with step-pools, energy loss varied only marginally with increasing flow rate in the nappe and transition flow regimes, while it increased in the skimming regime. Energy loss is positively correlated with the size of the recirculation zone, velocity in the recirculation zone and the vorticity. For the same flow rate, energy loss increased by 31.6% when the horizontal face inclination increased from 2° to 10°, while it decreased by 58.6% when the vertical face inclination increased from 40° to 70°. In a channel with several step-pools, cumulative energy loss is linearly related to the number of step-pools, for nappe and transition flows. However, it is a nonlinear function for skimming flows.

4 citations

01 Jan 2000-
Abstract: The goal of this study was to identify the flow conditions under which stable bedforms exist; provide the geometric characteristics of these bedforms; measure the magnitude of the streamwise velocity and energy dissipation factor; and determine the friction factor under various flow conditions and gravel sizes. Design criteria and recommendations for stable bedforms were provided upon the termination of this research. Stable bedforms are defined as those bedforms of which the spatial characteristics (height and spacing) do not change with time. The focus of this study was on streams with slopes greater than 3%, as clear design requirements for bed geomorphologic stability are lacking for these cases, and they are of particular interest in the design and retrofit of culverts for both anadromous and resident migratory fish passage.

2 citations

Journal ArticleDOI
11 Oct 2021-Scientific Reports
Abstract: The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes. Step-pools display spatio-temporal variations in bed and flow characteristics due to meso-scale units such as step, tread, base of step, and pool. Exclusive research on the effects of bed variations in step-pools on the flow dynamics is limited. Here, we conducted laboratory experiments on a physical model downscaled from a field site in the Western Ghats, Kerala, India. The results of Kruskal–Wallis ANOVA show significant differences in the velocity and turbulent intensities for the morphological units. A regression equation of the form Power-Allometric1 has been proposed to relate the normalized turbulent kinetic energy with the velocity magnitude. The present study also estimated the range of Reynolds shear stress and energy dissipation factor existent in the step-pool systems. The normalized values of Reynolds shear stress in the x–z plane ranged from − 19.477 to 13.729, and energy dissipation factors obtained for the three step-pool systems are 321, 207, and 123 W/m3; both the results reveal insufficient pool volume for adequate energy dissipation. The study concludes that while designing close-to-nature step-pool fish passes, pool dimensions should be finalized with respect to the target aquatic species.

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01 Jan 1959-
TL;DR: This book discusses the development of Uniform Flow and its applications, as well as the theory and analysis of open channel flow, and the design of channels for Uniform Flow.
Abstract: Chapter 1: Basic PrinciplesChapter 2: Open-Channel Flow and its ClassificationsChapter 3: Open Channels and Their PropertiesChapter 4: Energy and Momentum PrinciplesChapter 5: Critical Flow: Its Computation and ApplicationsChapter 6: Uniform FlowChapter 7: Development of Uniform Flow and Its FormulasChapter 8: Computation of Uniform FlowChapter 9: Design of Channels for Uniform FlowChapter 10: Theoretical Concepts of Boundary LayerChapter 11: Surface RoughnessChapter 12: Velocity Distribution and Instability of Uniform FlowChapter 13: Gradually Varied FlowChapter 14: Theory and AnalysisChapter 15: Methods of ComputationChapter 16: Practical ProblemsChapter 17: Spatially Varied FlowChapter 18: Rapidly Varied FlowChapter 19: Flow Over SpillwaysChapter 20: Hydraulic Jump and its Use as Energy DissipatorChapter 21: Flow in Channels of Non-Linear AlignmentChapter 22: Flow Through Nonprismatic Channel SectionsChapter 23: Unsteady FlowChapter 24: Gradually Varied Unsteady FlowChapter 25: Rapidly Varied Unsteady Flow Flood RoutingAppendices

5,006 citations

"Review of step-pool hydrodynamics i..." refers background in this paper

  • ...The famous Manning’s and Chezy’s equations can be applied only for steady uniform flow, where n values are developed exclusively for smallscale roughness (Chow, 1959), rendering it unsuitable for moderate and steeper mountain streams....


01 Jan 1953-
Abstract: Some hydraulic characteristics of stream channels — depth, width, velocity, and suspended load — are measured quantitatively and vary with discharge as simple power functions at a given river cross section. Similar variations in relation to discharge exist among the cross sections along the length of a river under the condition that discharge at all points is equal in frequency of occurrence. The functions derived for a given cross section and among various cross sections along the river differ only in numerical values of coefficients and exponents. These functions are:

2,402 citations

Journal ArticleDOI
Abstract: A classification of channel-reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types: colluvial, bedrock, and five alluvial channel types (cascade, step pool , plane bed, pool rime, and dune ripple). Coupling reach-level channel processes with the spatial arrangement of reach morphologies, their links to hillslope processes, and external forcing by confinement, ripar­ ian vegetation, and woody debris defines a process-based framework within which to assess channel condition and response potential in mountain drainage basins. Field investigations demonstrate character­ istic slope, grain size, shear stress, and roughness ranges for different reach types, observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad­ justed to the relative magnitudes of sediment supply and transport ca­ pacity. Steep alluvial channels (cascade and step pool) have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply, whereas low-gradient alluvial channels (pool rime and dune ripple) have lower transport capacity to supply ra­ tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge. General differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source, transport, and response segments, the spatial distribution of which provides a watershed-level conceptual model linking reach morphology and channel processes. These two scales of channel network classification define a framework within which to in­ vestigate spatial and temporal patterns of channel response in moun­ tain drainage basins.

1,762 citations

"Review of step-pool hydrodynamics i..." refers background in this paper

  • ...Although mountain streams have a significant role in providing aquatic habitat, supplying sediments to rivers and transmitting land-use disturbances from headwaters to the floodplains, there is relatively less research carried out to understand its flow phenomenon (Montgomery and Buffington, 1997)....


  • ...Mountain streams are typically categorized into three types of bed morphology: bedrock, alluvium and colluvium (Montgomery and Buffington, 1997)....


Journal ArticleDOI

532 citations

"Review of step-pool hydrodynamics i..." refers background or methods in this paper

  • ...…obtained velocity and measured velocity for the entire data set considered was evaluated using the resistance equations given by Strickler (1923), Keulegan (1938), Hey (1979), Bathurst (1985), Smart and Jäggi (1983) and Ferguson (2007) since these studies covered both simple and complex…...


  • ...The exact form of the pioneering Keulegan (1938) equation is given below, where ks is the equivalent roughness coefficient whose value is typically a multiple of Dm: 8 f 1=2 ¼ 6:25þ 5:75log R ks ð2Þ The power relations are typically of two types....


  • ...…based on hydraulic geometry. f ¼ 8gRSb u2 ð1Þ Semi-logarithmic relations are adopted from the boundary layer theory and pipe flow hydraulics and they relate relative submergence with f through a semi-logarithmic relation (Bathurst, 1985; Bray, 1979; Griffiths, 1981; Hey, 1979; Keulegan, 1938)....


  • ...In such cases, Manning’s empirical formula can be used to obtain an approximate flow velocity measurement (Keulegan, 1938)....


  • ...S ¼ Sf 0 þ Sf 00 ð16Þ The grain roughness coefficient f 0 was calculated using equation (2) from Keulegan (1938), by substituting ks ¼ D50 or as a suitable multiplier of D84 to allow for the presence of form roughness (Bathurst, 1985; Bray, 1979; Comiti et al., 2007; Curran and Wohl, 2003; David et…...


Journal ArticleDOI
Abstract: Onsite surveys and 75 measurements of discharge were made on 21 high-gradient streams (slopes greater than 0.002) for the purpose of computing the Manning roughness coefficient, n, and to provide data on the hydraulics of these streams. These data show that: (1) n varies inversely with depth, (2) n varies directly with slope, and (3) streams thought to be in the super-critical flow range were actually in the subcritical range. A simple and objective method was employed to develop an equation for predicting the n of high-gradient streams by using multiple-regression techniques and measurements of the slope and hydraulic radius. The average standard error of estimate of this prediction equation was 28% when tested with Colorado data. The equation was verified using other data available for high-gradient streams. Regime-flow equations for velocity and discharge also were developed.

452 citations

"Review of step-pool hydrodynamics i..." refers methods in this paper

  • ...…resistance equations are Manning’s roughness coefficient n, Chezy’s roughness coefficient C and the Darcy–Weisbach friction factor f (Bathurst, 1985; Jarrett, 1984; Rice et al., 1998), out of which only the Darcy–Weisbach friction factor is nondimensionless and is extensively used (Ferguson,…...


  • ...The commonly used roughness coefficients in flow resistance equations are Manning’s roughness coefficient n, Chezy’s roughness coefficient C and the Darcy–Weisbach friction factor f (Bathurst, 1985; Jarrett, 1984; Rice et al., 1998), out of which only the Darcy–Weisbach friction factor is nondimensionless and is extensively used (Ferguson, 2007; Nitsche et al....


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