The Impact of Intermittency on Bed Load Sediment Transport
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Abstract Sediment transport by wind or water near the threshold of grain motion is dominated by rare transport events. This intermittency makes it difficult to calibrate sediment transport laws, or to define an unambiguous threshold for grain entrainment, both of which are crucial for predicting sediment transport rates. We present a model that captures this intermittency and shows that the noisy statistics of sediment transport contain useful information about the sediment entrainment threshold and the variations in driving fluid stress. Using a combination of laboratory experiments and analytical results, we measure the threshold for grain entrainment in a novel way and introduce a new property, the “shear stress variability”, which predicts conditions under which transport will be intermittent. Our work suggests strategies for improving measurements and predictions of sediment flux and hints that the sediment transport law may change close to the threshold of motion.Keywords:
Intermittency
Entrainment (biomusicology)
Abstract Sediment transport by wind or water near the threshold of grain motion is dominated by rare transport events. This intermittency makes it difficult to calibrate sediment transport laws, or to define an unambiguous threshold for grain entrainment, both of which are crucial for predicting sediment transport rates. We present a model that captures this intermittency and shows that the noisy statistics of sediment transport contain useful information about the sediment entrainment threshold and the variations in driving fluid stress. Using a combination of laboratory experiments and analytical results, we measure the threshold for grain entrainment in a novel way and introduce a new property, the “shear stress variability”, which predicts conditions under which transport will be intermittent. Our work suggests strategies for improving measurements and predictions of sediment flux and hints that the sediment transport law may change close to the threshold of motion.
Intermittency
Entrainment (biomusicology)
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Abstract Information about sediment transport in the Common Meuse, an armoured gravel‐bed river, can be obtained by the determination of the relationship between sediment transport and discharge and integrating the relationship with respect to time, or by computing the differences between series of measured bed‐levels along the Common Meuse and integrating these differences. For three periods of 9, 8 and 17 years sediment transport computations are made with two series of relationships between sediment transport ( Q b ) and discharge ( Q ) in which the condition of the armour layer is taken into account. These sediment‐transport–discharge ( Q b & sol ; Q ) relationships are determined by local bed‐load transport measurements in the Common Meuse. At the beginning and the end of the first period (1978–1987) and at the end of the second period (1987–1995) bed levels have been measured by soundings. By the analysis of the measured bed levels at the beginning and the end of the two periods the sediment transport along the Common Meuse is estimated. The same analysis was carried out for the combined period (1978–1995). The yearly mean sediment transport computed by these two methods are compared. The necessity of carrying out bed‐load transport measurements at several locations in a cross‐section and over the entire range of discharges is clearly shown. Attention is paid to the advantages and disadvantages of the two methods and the need for applying more than one method to compute sediment transport. Copyright © 2001 John Wiley & Sons, Ltd.
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Sediment transport by wind or water near the threshold of grain motion is dominated by rare transport events. This intermittency makes it difficult to calibrate sediment transport laws, or to define an unambiguous threshold for grain entrainment, both of which are crucial for predicting sediment transport rates. We present a model that captures this intermittency and show that the noisy statistics of sediment transport contain useful information about the sediment entrainment threshold and the variations in driving fluid stress. Using a combination of laboratory experiments and analytical results, we measure the threshold for grain entrainment in a novel way and introduce a new property, the ``bed sensitivity'', which predicts conditions under which transport will be intermittent. Our work suggests strategies for improving measurements and predictions of sediment flux and hints that the sediment transport law may change close to the threshold of motion.
Intermittency
Entrainment (biomusicology)
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