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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Experiments 3a, b and c show that on average 85 % of all marked rock fragments were
mobilized after the passing of 45 goats. As figure 5 illustrates, the main direction of
translocation throughout all 3 experiments is forward downslope (segment 1) with an average
proportion of 57 % of all moved rock fragments. Also true for all 3 experiments is the fact
that significantly more rock fragments were pushed forward than backward (on average 62 %
to 28 %). Hence, the goats’ moving direction and slope direction seem to correlate with the
translocation direction of our rock fragments. As expected, the results of experiment 3c show
that gravity plays an increasingly important role once slope is steeper. Here, 86 % of all
moved rock fragments were relocated downslope, compared with 70 % in experiments 3a and
b combined. Furthermore, the input proportion in the forward directions (segments 1 and 4) is
heavily skewed in favor of the forward downslope compartment with a ratio of 71 % to 10 %,
compared with 44 % to 18 % and 56 % to 16 % in experiments 3a and b, respectively. This
indicates a change in the trajectory of the kicked rock fragments due to steeper slope. Rock
fragments that would come to a halt in segment 4 on a flatter slope, now land in segment 1.
This hypothesis is also nicely supported by the analysis of the sub segments 1a and b. Since
the input quantities are similar for both sub segments in experiments 3a and b, they do not
allow for a judgment of whether the goats’ moving direction or slope has a higher impact on
the rock fragments relocation. In experiment 3c, however, where slope is much steeper (11°),
the input in segment 1a is more than twice as high as in 1b. Likely, this result can be ascribed
to an additional input of rock fragments in 1a, which on flatter slopes would have remained in
segment 4.
Finally, the distribution of rock fragments across all 4 segments, i.e. all directions, is
noteworthy. The hooves’ impact cannot be easily translated into a forward-downslope kicking
direction of rock fragments. While this is true for the lion’s share of all measured rock
fragments, segments 2, 3 and 4 constantly contained at least some of the total quantity.
Interestingly, the highest mean translocation distances were not always recorded in the
forward-downslope direction. In fact, this was only the case in experiment 3b. In experiments
3a and 3c, the upslope segments 3 and 4, respectively, show the highest values. However,
since few rock fragments were moved into these segments and the mean is calculated, outliers
can easily affect the result.
As expected, the mean translocation distance increases with slope. Whereas it is 6.2 cm for
experiments 3a and b put together, the impact of gravity clearly surfaces in experiment 3c,
where it is 14.1 cm. On analyzing the results of the sub segments 1a (forward-forwarddownslope)
and 1b (downslope-forward) in all 3 experiments, the impetus of the factor slope
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