Sediment supply and local scouring at bed sills in high‐gradient streams

Marion, Andrea; Tregnaghi, Matteo; Tait, Simon

doi:10.1029/2005wr004124

Cited by 51 publications

(29 citation statements)

References 15 publications

(35 reference statements)

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“…Figure S2) started to increase after the discharge exceeded about 30.0 l/s (scaled to 5.4 m 3 /s) in CIFR T and CIFR runs. Since the local scour geometry has been reported to be influenced by GSD (Marion et al, 2004(Marion et al, , 2006, whether this discharge threshold remains the same with various grain size features needs further investigation in future. The well-defined step-pool morphology in Rio Cordon, Italy, only recovered from the buried bed channel (by an antecedent exceptional flood event) after the flood with the peak of 4.73 m 3 /s and return time of one to five years (Lenzi, 2001).…”

Section: Discussionmentioning

confidence: 98%

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Chendi

Hassan

et al. 2019

Earth Surf Processes Landf

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Exceptional flood events with a return period of about 50 years can be destructive to step‐pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step‐pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well‐graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro‐bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro‐bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step‐pool unit decreased as a power function from low to high flow, quantified as the ratio hc/HS, where hc is the critical water depth and HS is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step‐pool unit and the crucial role of hydrograph shape on the interaction during flow increase © 2019 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 98%

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Chendi

Hassan

et al. 2019

Earth Surf Processes Landf

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“…Empirical formulas to predict scour depth below low-head drop structures with non-cohesive bed materials have been compiled: Schoklitsch, 1935;Veronese, 1937;Kotoulas, 1967 (Whittaker andSchleiss, 1984); Bisaz and Tschopp, 1972;Aguirre Pe et al, 1980;Laursen and Flick, 1983;Laursen et al, 1986. Several important contributions on the subject of scour depth have been reviewed, including one contribution on cobble-lined drop structures: Smith and Murray, 1975;Laursen, 1984;Laursen et al, 1986;Whittaker and Jaggi, 1986;Lenzi et al, , 2004Marion et al, 2004Marion et al, , 2006Comiti et al, 2005. There is already a significant body of studies of bed stabilization with structural measures. Linder (1963) conducts a series of hydraulic model tests to develop a stream-bed stabilizer using sheet piling and rock sills for the Floyd River flood control project in Sioux City, Iowa (US Army Corps of Engineers, 1991).…”

Section: Introductionmentioning

confidence: 99%

Bed stability variations after check dam construction in torrential channels (South‐East Spain)

Conesa-García

López-Bermúdez

García-Lorenzo

2007

Earth Surf Processes Landf

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The effects of check dams on the bed stability of torrential channels have been analysed in several tributary basins of the Segura and Guadalentín rivers (South-East Spain). In order to illustrate the large variability in channel bed-forms and bed sediment sizes along the stream, 52 reaches of 150 m in length were surveyed. This variability is due to the behaviour of check dams, which depends on bedrock control, bed slope, channel roughness, lateral sediment input and a highly variable sediment transport capacity. Though the purpose of check dams is to diminish the boundary shear stress, reducing the longitudinal slope, and to stabilize the channel bed, downstream they reduce the volume of channel-stored material, favouring local scour processes, and upstream they can destabilize the sidewalls. The results enable us to evaluate the impact of every check dam on the bed morphology, distinguishing the structures installed in limy marl areas (e.g. catchment of the Cárcavo rambla, Cieza) and in schist and slate terrains (e.g. catchment of the Torrecilla rambla, close to Lorca). In the first type, bedrock and moderately thick granular beds predominate downstream from the check dams, so that the length of bedrock reaches and increase of roughness due to scour processes are the best indicators to verify its geomorphological effectiveness. On the other hand, the metamorphic areas drained by ramblas and gullies produce great quantities of gravel that are retained by check dams, creating more uniform and permeable beds, where the balance between sedimentation and scouring, and the ratio τ τ τ τ τ c84 /τ τ τ τ τ 0 (RBS), appear to be the parameters most frequently adopted to estimate the bed stability. Analysis of slope adjustments and the application of other indices to estimate the bed substrate stability (LRBS, SRI) and the structural influence of the dams (SIBS) corroborate the differences in bed stability found in the corrected reaches in each catchment.Major disruption of the natural regimes of large rivers, principally by damming and channelizing, has received extensive attention in the last decades (Petts, 1979;Graf, 1988;Brandt, 2000). However, relatively scant attention has been directed toward the responses of smaller streams to flood-control measures (Martínez Castroviejo et al., 1990;Martín Rosales, 1997). The problem of small-stream alteration is especially important in regions that are more densely populated, such as Japan, China, India and many parts of Europe. In an effort to develop low-cost means of stabilizing degrading small streams, several different types of low-head drop structure, some of them quite novel, have been developed.Determining their degree of efficiency requires an evaluation of which types of hydraulic, hydrological and geomorphological effect are caused upstream and downstream from these structures. In general, and especially in arid and semiarid environments, the spacing of check dams in a drainage network involves a sudden interruption in the conditions of transport, producing a rapid ...

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“…The shape of the scour hole and the regime of the associated hydraulic jump affect the erosional ability of the flow below the step. Scour depth has previously been shown to be dependent on step morphology [ Alexandrowicz , 1994; Lenzi et al , 2002] and sediment supply [e.g., Marion et al , 2006]. Step morphodynamics, in turn, can affect channel geometry and step morphology.…”

Section: Introductionmentioning

confidence: 99%

Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps

Wyrick¹,

Pasternack²

2008

J. Geophys. Res.

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[1] The river step is an important driver for geomorphic evolution in bedrock rivers, but the effect that variations in channel geometry upstream and downstream of a river step have on hydraulic jump regime and energy dissipation has not previously been investigated. The associated hydraulic jump is inherent to a river step and its regime is a primary control on step morphodynamics. In turn, the hydraulic jump regime is controlled by several variables as detailed in a new conceptual framework herein. Also in this study, a parsimonious semianalytical numerical model of step hydraulics is developed to quantify energy dissipation and delineate hydraulic jump regimes, accounting for discharge, jump submergence, and nonuniform channel geometry through a step. Despite remaining limitations in step theory, the model simulates how natural steps respond to a wide range of conditions. The model shows that hydraulic jump regime and energy dissipation exhibit greater sensitivity to channel nonuniformity as discharge increases and/or step height decreases. Also, channel conditions that create greater jump submergence lead to decreased energy dissipation, regardless of the discharge regime. The model also reinforces the common observation about gully erosion that downstream channel widening enhances upstream knickpoint migration. The new algorithm may be used to aid river engineering involving steps and could be useful for landscape evolution modeling.Citation: Wyrick, J. R., and G. B. Pasternack (2008), Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps,

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Sediment supply and local scouring at bed sills in high‐gradient streams

Cited by 51 publications

References 15 publications

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Experiment on morphological and hydraulic adjustments of step‐pool unit to flow increase

Bed stability variations after check dam construction in torrential channels (South‐East Spain)

Modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps

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