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

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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 247
Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen higher in trail zone (1.7 ha, trail area 545 m²), where the trail erosion rate reaches 692 Kg ha -1 per 600 goats. Outside the trail zone, the value is 44 Kg ha -1 per 600 goats. Figure 10: Trail distribution in the study area The translocation of rock fragments results in an almost complete workup of the rock fragment cover. According to CERDÀ (2001) rock fragments retard ponding and surface runoff and give greater steady state infiltration rates and smaller interrill runoff discharges, sediment concentrations and interrill erosion rates. He performed rainfall simulations with 55 mm h -1 for 120 min, in the middle of which he removed the rock fragment cover. The steadystate infiltration rate diminished from 44.5 to 27.5 mm h -1 , the runoff coefficient increased by the factor 3, sediment concentration by the factor 33 and the erosion rate by the factor 39. That means the rock fragments are an important erosion protection and if they are removed by animal trampling, the substrate below becomes vulnerable against other erosion processes. 248
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Stefan Wirtz Vom Fachbereich VI (Ge
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Danksagung Danksagung Die vorliegen
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Experimentelle Rinnenerosionsforsch
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