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Titel |
Modelling the migration of a mid-Pleistocene erosion wave in the Ardennes (western Europe) drainage network: approach and first implications |
VerfasserIn |
Arnaud Beckers, Benoît Bovy, Alain Demoulin |
Konferenz |
EGU General Assembly 2011
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250048478
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Zusammenfassung |
Model parameterization through adjustment to field data is a crucial step in the modelling and
the understanding of the drainage network response to tectonic or climatic perturbations.
Using a data set of 18 knickpoints that materialize the migration of a 0.7-Ma-old erosion
wave in the Ourthe catchment of northern Ardennes (western Europe) as a test case, we
explore the impact of various data fitting on the calibration of the detachment-limited stream
power model of river incision, from which a simple knickpoint celerity equation is derived.
Our results show that statistical least squares adjustments (or misfit functions) based either on
the stream-wise distances between observed and modelled knickpoint positions at time t =
0.7 Ma or on differences between observed (0.7 Ma) and modelled time at the actual
knickpoint locations yield significantly different values for the m (more exactly, m-n) and K
parameters of the model. As there is no physical reason to prefer one or the other
approach, we suggest that an intermediate least rectangles adjustment might be the
best compromise. In the Ourthe case, this leads to a m-n value lower than that
obtained from the classical distance adjustment (0.79 against 0.86), leading to an
increase in the non linear character of the dependence of knickpoint celerity on
discharge. If we now recall that m/n = c(1-b) (Whipple & Tucker, 1999, JGR 104B:
17661-17674), where c and b are the exponents of the power law relations respectively
linking discharge to drainage area and channel width to discharge, we can compare
the calculated m-n value with that derived from field measurements of channel
width, discharge and drainage area in the presently graded sections of the rivers.
Such data taken from Petit et al. (2005, BSGLg 46: 37-50) allow us to derive m-n
= 0.48 at equilibrium. As c may be considered constant, the higher m-n value
obtained from the knickpoint retreat modelling must be ascribed to a lower b, i.e., to a
channel narrowing associated with the transient phase of knickpoint migration. |
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