Hydraulics of a Large Channel Paved With Boulders

Thompson, Scott M.; Campbell, P.

doi:10.1080/00221687909499577

Cited by 107 publications

(74 citation statements)

References 3 publications

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“…The peak discharge of the 1987 jö kulhlaup was reconstructed for comparison with discharge measured directly during that event (Russell, 1989), providing validation of the hydraulic techniques used. Mean flow velocities for each channel cross section were calculated using three variants of the standard Manning resistance equation, as well as an adaptation of the Keulegan equation (Thompson and Campbell, 1979;others, 1999, 2007;Carrivick and others, 2004;Carrivick, 2007a). The Manning and Keulegan resistance equations require the input data: (1) energy gradient or water surface slope, (2) channel hydraulic radius and (3) grain roughness (Chow, 1959;Henderson, 1966;Maizels, 1983).…”

Section: Study Area and Methodsmentioning

confidence: 99%

A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland

et al. 2011

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ABSTRACT. Jö kulhlaups in 2007 and 2008 from an ice-dammed lake at the northern margin of Russell Glacier, West Greenland, marked the onset of a renewed jö kulhlaup cycle after 20 years of stability. We present a record of successive ice-dammed lake drainage events and associated ice-margin dynamics spanning $25 years. Robust calculations of lake volumes and peak discharges are made, based on intensive field surveys and utilizing high-spatial-resolution orthophotographs of the lake basin and ice margin. These data enable identification of controls on the behaviour of the ice-dammed lake and provide the first field-based examination of controls on jö kulhlaup magnitude and frequency for this system. We find that Russell Glacier jö kulhlaups have a much higher peak discharge than predicted by the Clague-Mathews relationship, which we attribute to an unusually short englacial/subglacial routeway and the presence of a thin ice dam that permits incomplete sealing of jö kulhlaup conduits between lake drainage events. Additionally, we demonstrate that the passage of jökulhlaups through an interlinked system of proglacial bedrock basins produces significant attenuation of peak discharge downstream. We highlight that improved understanding of jökulhlaup dynamics requires accurate information about ice-dammed lake volume and ice-proximal jö kulhlaup discharge.

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Section: Study Area and Methodsmentioning

confidence: 99%

A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland

et al. 2011

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“…where x is the hiding factor (x = 0.90; Parker, 1990), c and m are constants relating to the chosen flow resistance relationship (c = 0.37, m = 1.14; Thompson and Campbell, 1979), and τ c ⁎ 50 is the critical dimensionless shear stress to entrain the median clast size (τ c ⁎ 50 = 0.045).…”

Section: Flow Competence and Bed Materials Mobilitymentioning

confidence: 99%

Flood magnitude–frequency and lithologic control on bedrock river incision in post-orogenic terrain

Jansen

2006

Geomorphology

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Mixed bedrock-alluvial rivers-bedrock channels lined with a discontinuous alluvial cover-are key agents in the shaping of mountain belt topography by bedrock fluvial incision. Whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes, the present study investigates river incision processes in a post-orogenic (cratonic) landscape undergoing extremely low rates of incision (< 5 m/Ma). River incision processes are examined as a function of substrate lithology and the magnitude and frequency of formative flows along Sandy Creek gorge, a mixed bedrock-alluvial stream in arid SE-central Australia. Incision is focused along a bedrock channel with a partial alluvial cover arranged into riffle-pool macrobedforms that reflect interactions between rock structure and large-flood hydraulics. Variations in channel width and gradient determine longitudinal trends in mean shear stress (τ b ) and therefore also patterns of sediment transport and deposition. A steep and narrow, non-propagating knickzone (with 5% alluvial cover) coincides with a resistant quartzite unit that subdivides the gorge into three reaches according to different rock erodibility and channel morphology. The three reaches also separate distinct erosional styles: bedrock plucking (i.e. detachment-limited erosion) prevails along the knickzone, whereas along the upper and lower gorge rock incision is dependent upon large formative floods exceeding critical erosion thresholds (τ c ) for coarse boulder deposits that line 70% of the channel thalweg (i.e. transport-limited erosion).The mobility of coarse bed materials (up to 2 m diameter) during late Holocene palaeofloods of known magnitude and age is evaluated using step-backwater flow modelling in conjunction with two selective entrainment equations. A new approach for quantifying the formative flood magnitude in mixed bedrock-alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials; in this case the d 84 size fraction. A 350 m 3 /s formative flood fully mobilises the coarse alluvial cover with τ b ∼200-300 N/m 2 across the upper and lower gorge riffles, peaking over 500 N/m 2 in the knickzone. Such floods have an annual exceedance probability much less than 10 − 2 and possibly as low as 10 − 3 . The role of coarse alluvial cover in the gorge is discussed at two scales: (1) modulation of bedrock exposure at the reach-scale, coupled with adjustment to channel width and gradient, accommodates uniform incision across rocks of different erodibility in steady-state fashion; and (2) at the sub-reach scale where coarse boulder deposits (corresponding to τ b minima) cap topographic convexities in the rock floor, thereby restricting bedrock incision to rare large floods. While recent studies postulate that decreasing uplift rates during post-orogenic topographic decay might drive a shift to transport-limited conditions in river networks, observations here and elsewhere in post-orogenic settings sugge...

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“…Only these two grain-size percentiles (i.e., d 50 and d 90 ) were selected so that the contrast between the results is as large as possible. , 1976;Charlton et al, 1978;Ferro and Giordano, 1991;Green, 2005;Limerinos, 1970;Ugarte and Méndez, 1994), the power law (Charlton et al, 1978;López et al, 2008;Maynord, 1991) or other laws for high relative roughness flow, such as those by Aguirre-Pe and Fuentes (1990) or Thompson andCampbell (1979) (López et al, 2008). In the opposite sense, Bray (1979), using data from gravel and cobble-bed rivers with bankfull level, found no significant differences in the goodness-of-fit of the logarithmic laws and the power law in function of the grain-size percentile used (in his case d 50 , d 65 and d 90 ).…”

Section: Methodsmentioning

confidence: 99%

Flow resistance equations for mountain rivers

2009

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Three models of flow resistance (a Keulegan-type logarithmic law and two models developed for large-scale roughness conditions: the full logarithmic law and a model based on an inflectional velocity profile) were calibrated, validated and compared using an extensive database (N = 1,533) from rivers and flumes, representative of a wide hydraulic and geomorphologic range in the field of gravel-bed and mountain channels. It is preferable to apply the model based on an inflectional velocity profile in the relative submergence (y/d 90 ) interval between 0.5 and 15, while the full logarithmic law is preferable for values below 0.5. For high relative submergence, above 15, either the logarithmic law or the full logarithmic law can be applied. The models fitted to the coarser percentiles are preferable to those fitted to the median diameter, owing to the higher explanatory power achieved by setting a model, the smaller difference in the goodness-of-fit between the different models and the lower influence of the origin of the data (river or flume).Key words: friction factor; grain-size percentile; high-gradient streams; cross validation. Resumen Ecuaciones de resistencia al flujo para ríos de montañaSe han calibrado, validado y comparado tres modelos de resistencia al flujo (una ley logarítmica tipo Keulegan y dos modelos desarrollados para condiciones de alta rugosidad: la ley logarítmica completa y un modelo basado en un perfil de velocidad inflexional) empleando para ello una extensa base de datos (N = 1,533) de río y de laboratorio, representativa de un amplio intervalo hidráulico y geomorfológico en el ámbito de cauces de grava y de montaña. El modelo basado en un perfil de velocidad inflexional es preferible para su aplicación en el intervalo de sumersión relativa (y/d 90 ) comprendido entre 0.5 y 15, mientras que la ley logarítmica completa es preferible para valores inferiores a 0.5. Para sumersión relativa alta, por encima de 15, es posible aplicar indistintamente la ley logarítmica y la ley logarítmica completa. Son preferibles los modelos ajustados con los percentiles más gruesos que los ajustados con el diámetro mediano, debido a: la mayor capacidad explicativa alcanzada fijado un modelo, la menor diferencia en la bondad de ajuste entre los diferentes modelos y la menor influencia del origen de los datos (río o laboratorio).Palabras clave: factor de fricción; percentil granulométrico; cauces de fuerte pendiente; validación cruzada.

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Hydraulics of a Large Channel Paved With Boulders

Cited by 107 publications

References 3 publications

A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland

A new cycle of jökulhlaups at Russell Glacier, Kangerlussuaq, West Greenland

Flood magnitude–frequency and lithologic control on bedrock river incision in post-orogenic terrain

Flow resistance equations for mountain rivers

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