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| Titel |
Renewing confidence in the 3/2 power-law |
| VerfasserIn |
F. Métivier, Y. Liu, C. Narteau, E. Lajeunesse, O. Devauchelle, B. Ye, M. Tal, P. Meunier |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024704
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| Zusammenfassung |
| Numerous transport relationships have been devised throughout the years to predict
bedload transport in rivers, particularly gravel bed rivers for which bedload exerts a
strong control on river morphology. Transport relationships based on laboratory
experiments are typically expressed in terms of bed shear stress and take the form of
a power law regime with a 3/2 exponent above a critical value for the inception
of motion. However, available studies from natural gravel bed streams show that
the conditions for such an asymptotic regime to be observed rarely exist. Using
an extensive survey carried out over three years in a mountain gravel bed stream
in China, we show that, despite high variability in measurements made in-situ, it
is possible to derive a clear power law relationship with an exponent 3/2 for the
bulk transport over more than 2 orders of magnitude of the bed shear stress. This is
done through the development of a new integral technique that averages out the
variability of bedload measurements. The same conclusions apply for smaller samples at
different sites along the river, as well as for previously published datasets that are
based on individual point measurements instead of cross-section averaging. This
result highlights problems in how field surveys have been performed over the last
decades and demonstrates the need to make individual point measurements at different
points along the same section. When considering the entire range of grain sizes
and the entire dataset, our data show that the threshold for motion inception most
probably corresponds to the threshold of the smallest grains caught by the sampler. |
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