Journal of Geophysical Research. Geologic principles and processes. Dieses Dialogfeld wird über die Schaltfläche "Darstellung ändern" aufgerufen und die Einstellungen darin sind je nach Diagrammtyp unterschiedlich. This is called armouring effect.
The following table gives the approximate required Rouse numbers for transport as bed load , suspended load , and wash load. The settling velocity also called the "fall velocity" or " terminal velocity " is a function of the particle Reynolds number. Generally, for small particles laminar approximation , it can be calculated with Stokes' Law.
For larger particles turbulent particle Reynolds numbers , fall velocity is calculated with the turbulent drag law. Dietrich compiled a large amount of published data to which he empirically fit settling velocity curves.
In this equation w s is the sediment settling velocity, g is acceleration due to gravity, and D is mean sediment diameter. The expression for fall velocity can be simplified so that it can be solved only in terms of D.
From these parameters, the fall velocity is given by the expression:. In , Filip Hjulström created the Hjulström curve , a graph which shows the relationship between the size of sediment and the velocity required to erode lift it , transport it, or deposit it.
This curve has no more than a historical value nowadays, although its simplicity is still attractive. Among the drawbacks of this curve are that it does not take the water depth into account and more importantly, that it does not show that sedimentation is caused by flow velocity deceleration and erosion is caused by flow acceleration.
The dimensionless Shields diagram is now unanimously accepted for initiation of sediment motion in rivers. Formulas to calculate sediment transport rate exist for sediment moving in several different parts of the flow. These formulas are often segregated into bed load , suspended load , and wash load. They may sometimes also be segregated into bed material load and wash load. Bed load moves by rolling, sliding, and hopping or saltating over the bed, and moves at a small fraction of the fluid flow velocity.
However, the bed material load the bed load plus the portion of the suspended load which comprises material derived from the bed is often dominated by bed load, especially in gravel-bed rivers.
This bed material load is the only part of the sediment load that actively interacts with the bed. As the bed load is an important component of that, it plays a major role in controlling the morphology of the channel. Bed load transport rates are usually expressed as being related to excess dimensionless shear stress raised to some power. Excess dimensionless shear stress is a nondimensional measure of bed shear stress about the threshold for motion.
Bed load transport rates may also be given by a ratio of bed shear stress to critical shear stress, which is equivalent in both the dimensional and nondimensional cases. Due to the difficulty of estimating bed load transport rates, these equations are typically only suitable for the situations for which they were designed.
The transport formula of Meyer-Peter and Müller, originally developed in ,  was designed for well- sorted fine gravel at a transport stage of about 8. Because of its broad use, some revisions to the formula have taken place over the years that show that the coefficient on the left "8" above is a function of the transport stage: The variations in the coefficient were later generalized as a function of dimensionless shear stress: In , Peter Wilcock and Joanna Crowe now Joanna Curran published a sediment transport formula that works with multiple grain sizes across the sand and gravel range.
Their expression is more complicated than the basic sediment transport rules such as that of Meyer-Peter and Müller because it takes into account multiple grain sizes: The "hiding function" takes into account the fact that, while small grains are inherently more mobile than large grains, on a mixed-grain-size bed, they may be trapped in deep pockets between large grains.
Likewise, a large grain on a bed of small particles will be stuck in a much smaller pocket than if it were on a bed of grains of the same size.
In gravel-bed rivers, this can cause "equal mobility", in which small grains can move just as easily as large ones. Their model is based on the transport stage, or ratio of bed shear stress to critical shear stress for the initiation of grain motion.
In , Peter Wilcock and Kenworthy T. Likewise, a large grain on a bed of small particles will be stuck in a much smaller pocket than if it were on a bed of grains of the same size, which the Meyer-Peter and Müller formula refers to. Their model is based on the transport stage, i.
The critical shear stress that represents the incipient motion for each of the two fractions is consistent with established values in the limit of pure sand and gravel beds and shows a sharp change with increasing sand content over the transition from a clast- to matrix-supported bed.
For the case in which sand fraction is transported by the current over and through an immobile gravel bed, Kuhnle et al. It is worth mentioning that Kuhnle et al. Therefore, the sand bed load formula follows as: Suspended load is carried in the lower to middle parts of the flow, and moves at a large fraction of the mean flow velocity in the stream. A common characterization of suspended sediment concentration in a flow is given by the Rouse Profile.
It is given by the expression:. The Rouse profile characterizes sediment concentrations because the Rouse number includes both turbulent mixing and settling under the weight of the particles. Turbulent mixing results in the net motion of particles from regions of high concentrations to low concentrations.
Because particles settle downward, for all cases where the particles are not neutrally buoyant or sufficiently light that this settling velocity is negligible, there is a net negative concentration gradient as one goes upward in the flow.
The Rouse Profile therefore gives the concentration profile that provides a balance between turbulent mixing net upwards of sediment and the downwards settling velocity of each particle. Bed material load comprises the bed load and the portion of the suspended load that is sourced from the bed. Three common bed material transport relations are the "Ackers-White",  "Engelund-Hansen", "Yang" formulae.
The first is for sand to granule -size gravel, and the second and third are for sand  though Yang later expanded his formula to include fine gravel. That all of these formulae cover the sand-size range and two of them are exclusively for sand is that the sediment in sand-bed rivers is commonly moved simultaneously as bed and suspended load.
The bed material load formula of Engelund and Hansen is the only one to not include some kind of critical value for the initiation of sediment transport. The Engelund-Hansen formula is one of the few sediment transport formulae in which a threshold "critical shear stress" is absent.
Wash load is carried within the water column as part of the flow, and therefore moves with the mean velocity of main stream. Wash load concentrations are approximately uniform in the water column.
This is described by the endmember case in which the Rouse number is equal to 0 i. Some authors have attempted formulations for the total sediment load carried in water. From Wikipedia, the free encyclopedia.
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Brad; Arnault, Olivier Journal of Marine Systems. Applied Mathematical Modelling , Elsevier, Vol. The Hydraulics of Open Channel Flow: Butterworth-Heinemann, 2nd edition, Oxford, UK, pages.
Surface processes and landscape evolution. Retrieved 23 December Last accessed 26 Dec Massachusetts Institute of Technology. Formulas for bed-load transport.
Journal of Hydraulic Engineering. Journal of the Hydraulics Division. Modelling fine sediment transport over an immobile gravel bed. Sediment transport processes in coastal environments. Virginia Institute of Marine Science. Archived from the original PDF on 28 May Retrieved 25 December New Approach and Analysis". Yahya 14—16 October International Conference on Urban Hydrology for the 21st Century.
Journal of Geophysical Research. Drainage basin Drainage system geomorphology Estuary Strahler number stream order River valley River delta River sinuosity.
Canyon Knickpoint Plunge pool. Ait Antidune Dune Current ripple. Aggradation Base level Degradation geology Erosion and tectonics River rejuvenation. Es stehen vier vordefinierte Farbschemen sowie ein benutzerdefiniertes Farbschema zur Verfügung. Das auf dem Register ausgewählte Farbschema wird im Diagramm verwendet. Auf diesem Register können die Schriftarteigenschaften des Diagrammtitels und der Legende definiert werden. Wenn Sie auf diese Schaltfläche klicken, haben Sie auch die Option, die Diagrammeinstellungen auf die Standardeinstellungen zurückzusetzen.
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