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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
naturally developed. Rill 3 has developed on an old rotational slump and is the deepest incised
of the three rills. The deep incision suggests a more intense activity of the rill, but in the
experiments, the used 72l water did not reach the rill’s end. That means, that for development
and evolution of this rill, a much higher water quantity is needed as used in the experiments.
The estimated area of the catchments of rill 1 and rill 2 was 450 and 400 m² respectively. In
the rill catchments rainfall simulations were accomplished and the results are used to get a
ballpark estimation of the water amounts that can reach the rill at least for the given soil
moisture situation and the experimental rainfall intensity of 40 mm h -1 . Under a rainfall
intensity of 40 mm h -1 , rill 1 can expect a runoff of about 1.3 l s -1 , rill 2 even 4.15 l s -1 , these
values are about 10 to 25 times higher than the used input discharge rate of 0.15 l s -1 for each
rill. The rainfall simulation in the catchment of rill 1 reached a sediment concentration of 0.7
g l -1 , the average of the two runs of RE1 was 0.73 g l -1 , so there is no clear difference between
rill erosion and sheet erosion in this case, because the used quantity of water was not
sufficient to lead to further rill incision. The two rainfall simulations in the catchment of rill 2
reached an average sediment concentration of 1.38 g l -1 , the two runs of RE2 reached an
average of 1.52 g l -1 .
At the outlet of the Arnás catchment, SEEGER et al. (2005) measured runoff values as well as
sediment concentrations. The average sediment concentrations ranged between 0.03 and 2.29
g l -1 , with maximum values between 0.09 and 4.8 g l -1 . In the rill experiments, the maximum
sediment concentrations ranged between 1.59 and 6.31 g l -1 thus being in the same range than
the values of the whole Arnás catchment. It is not possible to compare the runoff values of the
rill experiments with the runoff values of the catchment because rill and river are different
forms and there are different processes proceeding. What we can do is to compare the runoff
values of the rill's catchment with the Arnás catchment: The area of the Arnás catchment is
284 ha, the average runoff values are between 48 and 708 l s -1 . For a catchment of 450 m² (rill
1) and 400 m² (rill 2) the theoretical runoff values would reach values between 0.008 and 0.11
l s -1 and between 0.007 and 0.1 l s -1 . The maximum values between 87 and 2347 l s -1 of the
Arnás catchment calculated for the rill catchments are between 0.014 and 0.37 l s -1 and
between 0.012 and 0.34 l s -1 . The used inflow was 0.15 l s -1 and this value caused the same
sediment concentration range as measured at the Arnás catchment outlet. The rainfall
simulations in the rill catchments show, that a rainfall intensity 40 mm h -1 could cause an
inflow in the rills of 1.3 for rill 1 or even 4.15 l s -1 for rill 2 (table 2).
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