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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Amounts of material which were moved on existing trails parallel to contour lines range
between the values measured on the abandoned fields in downslope direction with 8.5° and
12° slopes (experiment 1).
In a first experiment, we changed the running speed after the 5 th run and measured fine
material as well rock fragment translocation. In a second experiment with constant slow
running speed, we wanted to ensure to have measured the influence of different speed in the
first experiment, not the influence of a longer trampling time and higher animal quantity.
In the first experiment (figure 4a) rock fragments were not moved in the first 5 slow runs.
From run 6 onwards, the running speed of the animals was increased so that the goats were
now really 'running' along the trail, just in a way that can be regarded as typical for faster
movements of flocks. This faster movement lead to an increase of the translocation quantity
by the factor five, but with a temporal lag, because it was recorded only in the 7 th run.
Afterwards this trend decreased. Now, in addition to the higher fine material amount, rock
fragments were moved in runs 7 to 10. Their proportion rose and fell from 31 % in the 7 th run
over 35 % and 29 % down to 9 % in the last run. Altogether 4134 g of material was moved in
this experiment, 1237 g or 30 % of this material were rock fragments (see figure 4a).
In the second experiment, hardly any rock fragments were present on the plot. In mean, 145 g
material was moved in each run, this is similar to the 155 g measured in the slow runs in
experiment 2a.
Interpretation:
The similar mean values of the 4 slow runs in experiment 2a and the 9 runs in experiment 2b
show that the differences between the slow and the fast runs in experiment 2a are caused by
the different running speeds and not by trampling time and animal quantity.
In the trail experiment, the measured translocation rates parallel to contour lines reached
values around 1.3 g m -2 per goat for the slow runs which is comparable to the values measured
on the abandoned field. At the higher running speed, as it is more typical for the trails, the
translocation rate was five times higher with 5.9 g m -2 per goat. In the following experiment,
it is clearly to see that the speed influences the translocation rate and not the longer trampling
time and the higher number of animals. That means the running speed is an important
parameter for the quantity of translocated material. The movement of rock fragments again
can only be observed after the passing of about 300 goats.
3.3 Translocation direction and distance of rock fragments
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