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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
4 Discussion
The calculated translocation rates increase with slope and with the running speed of the
animals, thus conforming with theoretical expectations. All values are considered to be
explicitly higher than a tolerable soil erosion rate for completely mechanized agriculture. The
influence of slope has also been shown by OOSTWOUD WIJDENES et al. (2001). The
measured transport rates on a 50 % slope were twice as high as on a 20 % slope. The total
amount of loosened material by trampling of 6.6 Kg m -2 on the test plots has also to be
evaluated as very high. The provided loose material can easily be eroded by wind and water
erosion processes (cf. our rill experiments).
The trails in the study area are distributed very irregularly (see figure 10). The total trail
density is 247 m ha -1 ; 13 985 m ha -1 in the trail zone and 68 m ha -1 outside this zone.
Assuming a mean trail width of 30 cm, the total trail area takes up 705 m²; 545 m² in the trail
zone and 160 m² outside. Regarding the proportions of the total trail area, the values are 0.7 %
for the whole study area, 3 % in the trail zone and 0.2 % outside the trail zone (see table 2).
Table 2: Trails length and area sizes of different landscape units in the test area
Value
% of total area
Trail length in Trail zone [m] 1818 -
Trail length outside Trail zone[m] 532 -
Total trail length [m] 2350 -
Trail zone [m²] 17300 18
Abandoned fields [m²] 49000 51
Steep slopes [m²] 27830 29
Untreated zones [m²] 1300 2
Total area study site [m²] 95430 -
On the trails, sheep run similarly fast and close as simulated in our experiments, so we can use
our measured values to calculate trail erosion rates: Parallel to contour lines (in and against
running direction), each slow moving goat can translocate 1.3 g m -2 , and, if speed is
increased, the value can reach 5.9 g m -2 . For an extrapolation, we assume an average value of
3.6 g m -2 per goat and the same slopes as in our experiments, since the plots were
representative for trails in the study site. The total area is 9.5 ha, the trail area is 705 m²,
meaning the trail erosion rate reaches 160 Kg ha -1 per 600 goats. This value should clearly be
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