Stefan Wirtz Vom Fachbereich VI (Geographie/Geowissenschaften ...

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
The same rill was tested with and without goat trampling. The rill had an average slope of
8.8° and a maximum slope of 15.2°. The tested flow length is 16 m. Gravel content was 30%,
antecedent soil moisture 3 %, vegetation cover about 20 % and rock fragment cover was 60
%. The maximum depth of the rill was 10 cm and the maximum width about 40 cm. Grain
density was 2.69 Mg m -3 and (dry) bulk density was 1.44 Mg m -3 .
Methodology for analysis:
We used various methodological approaches to describe and illustrate our results:
In order to describe the results, different methodological approaches were used:
In experiment 1, the translocation quantity [g] is given. The translocated material is
removed from a defined test site area and collected in Gerlach Troughs. This quantity refers to
an area of 2 m² and 60 goats per run; the cumulative values represent 600 goats. As it is a
downslope mobilization, we can additionally state the translocation flux, i.e. the
translocation quantity per unit length in downslope direction. As the downslope length is 1 m,
the translocation flux is equal to the translocation quantity. The translocation quantity is
measured over the test plot length of 2 m, which leads to the following equation: translocation
flux [g m -1 ] = translocation quantity / 2. The translocation rate can be calculated from the
translocation quantity. It refers to 1 m² and one goat: translocation rate = translocation
quantity / 120.
In experiment 2 we use the translocation quantity and the translocation rate. The translocation
flux is not used because the values are not the result of a downslope movement. In this
experiment it is noteworthy that each trough collects the material from an area of 2 m², so
cumulated material from both troughs refers to 4 m². Additionally, in experiment 2, we
discuss a trail erosion rate. This value is given in Mg per ha and 600 goats, calculated from
the translocation rate in g per m² and goat. This calculation is representative in this case,
because on trails, the goats run similarily fast and similarily close as in our experiments.
In experiment 3, we calculate a net mean downslope translocation rate for each individual
rock fragment per experiment: Net mean downslope translocation rate = (downslope quantity
x downslope mean distance) - (upslope quantity x upslope mean distance) / all spread out rock
fragments.
In experiment 4, the loosening quantity was measured by brushing off and collecting the
loosened material from the flat test plot. The quantity is given in [g], referring to an area of 2
m² and 60 goats in each run. The loosening rate refers to 1 m² and 1 goat, leading to:
loosening rate = loosening quantity / 120.
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