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| Titel |
Parameterisation of a soil detachment model using rainfall simulation experiments |
| VerfasserIn |
Ulrike Scherer, Erwin Zehe, Klaus Traebing, Kai Gerlinger |
| 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 |
250049146
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| Zusammenfassung |
| Soil particle detachment is a key process affecting water erosion, since it determines the
amount of sediment that is potentially transferred to surface water bodies. Detachment of soil
particles depends on various factors such as hydro-meteorological forcing, soil hydraulic and
mechanical properties, type of crop and tillage practice. As with most other sub processes that
determine water erosion, particle detachment is only directly observable at small scales
within laboratory and field experiments. Process-based numerical erosion models are thus
used for extrapolating these findings from the plot scale to the scale of small catchments in
order to quantify sediment yields.
The objective of this study is to derive and parameterise a detachment approach that
balances simplicity and necessary process complexity to be implemented in a process-based
erosion model applicable at the scale of small catchments. In the proposed model the
attacking forces of rainfall (characterised as momentum flux of rainfall) and overland flow
(characterised as shear stress) are combined and related to the detachment rate.
The resisting forces of the soil are characterised by two empiric parameters: a)
erosion resistance fcrit, which is a threshold of the attacking forces that has to be
exceeded to initiate particle detachment and b) erodibility parameter p1, which
represents the linear increase of the detachment rate once the erosion resistance is
overcome. The empiric parameters of the detachment model are determined for
cultivated loess soils using two different data sets from rainfall simulation experiments.
On the one hand, data from laboratory experiments that were carried out under
varying conditions of rainfall and overland flow using identically prepared loess soil
samples (published by Schmidt, 1996) were used to determine p1. On the other hand,
data from 58 rainfall experiments performed on 24 m2 plots in the Weiherbach
catchment (Southwest Germany) were used to determine the erosion resistance fcrit for
varying soil conditions. For the procedure of determining fcrit, we assumed the
erodibility parameter p1 to be constant for the conventionally tilled silt loam soils in the
Weiherbach catchment and exclusively varied the erosion resistance parameter fcrit to
characterise particle detachment for the different field experiments. This approach
ensured that determination of fcrit was a well posed problem with a unique solution
to facilitate the prediction and regionalisation of the resistance of the soil against
detachment. We found evidence that cultivation was the first order control of the
erosion resistance: Crops that are cultivated in rows were strongly susceptible to
detachment because runoff is channelled along the intermediate areas of plant rows. Mean
erosion resistance was thus minimal for these sites. For bare soils we found a strong
correlation between the erosion resistance, surface roughness and clay content. |
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