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| Titel |
Factors of knickpoint migration on the moderately uplifted Ardennes Plateau, Western Europe |
| VerfasserIn |
A. Beckers, B. Bovy, A. Demoulin |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062556
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| Zusammenfassung |
| In the last two decades, much research has been devoted to the development and refinement
of numerical models of river incision. In settings of prevailing bedrock channel erosion,
numerous studies used field data, notably knickpoint data, to calibrate the widely
acknowledged stream power model of incision and to discuss the specific impact of
various variables (e.g., sediment load, channel width) not appearing explicitly in the
model’s simplest form. However, most of these studies were conducted in areas of
very active tectonics and high relief, thus displaying an exacerbated geomorphic
response to the tectonic signal. Here, we analyze the traces left in the drainage
network 0.7 My after the NE Ardennes region (western Europe) underwent a moderate
100-150 m uplift. We identify a set of knickpoints that have travelled far upstream
in the Ourthe catchment. Because time becomes a more sensitive variable than
distance near the headwaters, we fit the stream power model to the data by minimizing
time residuals (i.e., the differences between 0.7 My and the modelled times for the
knickpoints to reach their actual location) rather than distance residuals. Our best
fit of the stream power model parameters yields m/n = 0.75 and K = 4.63 10-8
m-0.5y-1. We suggest that the discrepancy with the m/n value of ~0.5 obtained
from field and long profile data of the currently graded downstream part of the
catchment’s streams points to a narrowing of the bedrock channel at the passage of a
knickpoint. Then, the time residuals of the model fit are regressed against quantitative
expressions of bedrock resistance to erosion and junction crossing, showing that
both variables significantly affect knickpoint migration. In particular, most of the
small tributaries with highly delayed knickpoints display all features characteristic
of hanging valleys. However, not all such small streams have developed hanging
valleys, and further research is needed to unravel how other controls, e.g., amount
and size of the tributary bed load, are determining for the creation of such valleys. |
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