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| Titel |
Modelling uncertainty in short-term catchment erosion rates |
| VerfasserIn |
Georgie Bennett, Peter Molnar, Oliver Korup, Paolo Burlando |
| 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 |
250053110
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| Zusammenfassung |
| Several studies have presented the discrepancies between erosion rates measured over
different timescales for catchments worldwide. We focus on those comparing short term
erosion rates spanning 100 to 101 years, obtained by river load sampling and from
sedimentation rates in reservoirs and lakes, and long term erosion rates spanning 103 to 104
years, obtained by cosmogenic nuclide dating. Conflicting relationships exist between short
and long term rates for different regions of the world. Short term rates exceed long term rates
by orders of magnitude in some regions, whilst in others the opposite relationship occurs,
notably in glaciated basins. Elsewhere short and long term rates appear to be in
equilibrium.
Two fundamental problems exist with the short term erosion rates used in such
comparisons. The first is the assumption that sediment yield is representative of the erosion
rate. Sediment storage may significantly modulate the transfer of sediment from source to
sink and may result in both temporary decreases and increases in sediment yield,
thus affecting the calculated erosion rates. The second problem is the inability to
capture the long term behaviour of the system in the short sampling window. For the
comparison of short and long term erosion rates it is therefore important to quantify
the possible uncertainty in the published short term rates resulting from these two
factors.
We use a simple conceptual model, based on the linear reservoir theory, to quantify the
uncertainty in catchment sediment yield and thus erosion rate. In particular we
investigate how uncertainty is a function of statistical characteristics of the external
forcing, formalized here as a stochastic event-based process, and the storage capacity
of the catchment, as determined by the mean residence time of sediment in the
system. We take several catchments for which short and long term erosion rates are
available. For each catchment a time-series of sediment output is generated with a long
term mean validated with the observed long term erosion rate. We then repeatedly
sample from the time-series, with a sampling window that represents the short-term
erosion rate record length, to obtain a probability distribution of erosion rates. Our
results show how sampling record length, the nature of external forcing and sediment
residence time interact to produce uncertainty in short-term erosion rates observed in
different catchments worldwide, raising questions about comparisons made between
these and long term erosion rates and interpretations based on these comparisons. |
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