Darcy‐Weisbach Roughness Coefficients for Gravel and Cobble Surfaces

Gilley, John E.; Kottwitz, Eugene R.; Wieman, Gary A.

doi:10.1061/(asce)0733-9437(1992)118:1(104)

Cited by 42 publications

(37 citation statements)

References 10 publications

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“…In this model, k w is given a value of 10 m (m 3 s −1 ) −1/2 , which is reasonable for natural rivers (Leopold and Maddock, 1953), but the value can range between 1 and 10 due to differences in runoff variability, substrate properties, and sediment load (Whipple et al, 2013). The friction factor, F , is the Darcy-Weisbach friction factor, which can range from 0.01-1.0 for natural rivers (Gilley et al, 1992;Hin et al, 2008). With a lower friction factor (representing smooth channel walls), the lateral erosion ratio would be higher due to less energy being dissipated on the channel walls, leaving more energy available for lateral erosion.…”

Section: Lateral Erosion Theorymentioning

confidence: 99%

Developing and exploring a theory for the lateral erosion of bedrock channels for use in landscape evolution models

Langston

Tucker

2018

Earth Surf. Dynam.

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Abstract. Understanding how a bedrock river erodes its banks laterally is a frontier in geomorphology. Theories for the vertical incision of bedrock channels are widely implemented in the current generation of landscape evolution models. However, in general existing models do not seek to implement the lateral migration of bedrock channel walls. This is problematic, as modeling geomorphic processes such as terrace formation and hillslopechannel coupling depends on the accurate simulation of valley widening. We have developed and implemented a theory for the lateral migration of bedrock channel walls in a catchment-scale landscape evolution model. Two model formulations are presented, one representing the slow process of widening a bedrock canyon and the other representing undercutting, slumping, and rapid downstream sediment transport that occurs in softer bedrock. Model experiments were run with a range of values for bedrock erodibility and tendency towards transport-or detachment-limited behavior and varying magnitudes of sediment flux and water discharge in order to determine the role that each plays in the development of wide bedrock valleys. The results show that this simple, physicsbased theory for the lateral erosion of bedrock channels produces bedrock valleys that are many times wider than the grid discretization scale. This theory for the lateral erosion of bedrock channel walls and the numerical implementation of the theory in a catchment-scale landscape evolution model is a significant first step towards understanding the factors that control the rates and spatial extent of wide bedrock valleys.

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Section: Lateral Erosion Theorymentioning

confidence: 99%

Developing and exploring a theory for the lateral erosion of bedrock channels for use in landscape evolution models

Langston

Tucker

2018

Earth Surf. Dynam.

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“…The data from [21] for rigid vegetation (C d0 = 1) also confirms the validity of the model for circular cylinders. The model is also compared with the results from [23], which are expressed in terms of Reynolds number R e = Uh/ν (Figures 9 and 10). They are a good example of the model validity for emergent-submerged transition and large natural roughness elements.…”

Section: Validation Of Friction Coefficients For River Flowsmentioning

confidence: 99%

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

Cassan

Roux

Garambois

2017

Water

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A friction model resulting from investigations into macro-roughness elements in fishways has been compared with a broad range of studies in the literature under very different bed configurations. In the context of flood modelling or aquatic habitats, the aim of the study is to show that the formulation is applicable to both emergent or submerged obstacles with either low or high obstacle concentrations. In the emergent case, the model takes into account free surface variations at large Froude numbers. In the submerged case, a vegetation model based on the double-averaging concept is used with a specific turbulence closure model. Calculation of the flow in the roughness elements gives the total hydraulic resistance uniquely as a function of the obstacles' drag coefficient. The results show that the model is highly robust for all the rough beds tested. The averaged accuracy of the model is about 20% for the discharge calculation. In particular, we obtain the known values for the limiting cases of low confinement, as in the case of sandy beds.

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“…Chow (1959) and Savat (1980) studied the flume experiments on rill; the results indicate a progressive decrease in hydraulic roughness (n) with increased Reynolds number (Rn). In a case, if depth of water is less than the size of the physical roughness coefficient, then Mannings Roughness coefficient increases in correspondence with increase in Rn values (Govers, 1992;Abrahams et al, 1986;Abrahams & Parsons, 1994;Gilley et al, 1992;Prosser & Dietrich, 1995). The spatial variability of rilling process depends on flow character controlled by channel roughness and expressed as Reynolds number (Rn) and Froude number (Nearing et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

Rill Hydraulics - An Experimental Study on Gully Basin in Lateritic Upland of Paschim Medinipur, West Bengal, India

Shit¹,

Maiti²

2012

JGG

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This paper reports the results of field investigations aimed to establish relationship between morphologic and hydraulic characteristics of rills. A rill network within a small Rangamati Gully Basin, on the bank of Kansai at Paschim Medinipur, in West Bengal, India of 256 m 2 was mapped. Experimental basin is exposed to natural rainfall of varying intensity and characterised with an average of 25-35% slope gradient. The depth, length, gradient, width, runoff contributing areas of all the 33 rills within the basin were recorded and thoroughly mapped. Present study incorporates close monitoring of runoff and velocity along the channels during a storm on 31.08.2010 at 15 minutes interval using dye tracer technique. The velocity along each rill was linked with gradient, width-depth ratio and Manning's roughness coefficient. Analysis shows that flow velocity is not directly controlled by rill gradient (R 2 =0.15), but is influenced by hydraulic roughness coefficient (R 2 =0.53). Finally, the relationship between Reynolds number and Froude number reveals that sub-critical turbulent flow is responsible for rilling process. No significant relationship between W/D ratio and channel roughness (n) can be established (R 2 =0.083) by the present study.

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Darcy‐Weisbach Roughness Coefficients for Gravel and Cobble Surfaces

Cited by 42 publications

References 10 publications

Developing and exploring a theory for the lateral erosion of bedrock channels for use in landscape evolution models

Developing and exploring a theory for the lateral erosion of bedrock channels for use in landscape evolution models

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

Rill Hydraulics - An Experimental Study on Gully Basin in Lateritic Upland of Paschim Medinipur, West Bengal, India

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