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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Table 6: Comparison of the runoff values of the Arnás catchment and the rill catchments; c.a.
= catchment area
Arnás c.a. 284 ha RE1 c.a. 450 m² RE2 c.a. 400 m²
specific average runoff [l s -1 /m²] 0.0001 0.00007 0.00008
specific runoff peak [l s -1 /m²] 0.0004 0.0001 0.0002
It is to notice, that the connectivity between rill and river is not given in each case. The
sediment and the water from the rill may not reach the river. The river transports the material
from those areas that have a connectivity to the river. The trails improve the connectivity, but
in some cases, it is not sufficient.
Accordingly the rills can be regarded as very effective sediment providers for the receiving
waters in a catchment because they can cause heavy sediment losses with relatively low
runoff amounts: the calculated specific runoff values of the rills are clearly lower than the
specific runoff values of the Arnás catchment. But this lower specific runoffs reach the same
sediment concentrations as the Arnás catchment (table 6).
The results clearly indicate that the rill erosion in the Arnás catchment, despite the relatively
low measured values, is characterized by a high efficiency.
The given standardized experimental setup makes it possible to compare different rills and to
take statements about their efficiency for runoff and sediment budget of a catchment. Only
with comparable conditions concerning water quantity and inflow intensity, it becomes
possible to achieve appropriate statements on the basis of the measured results and to compare
single experiments to each other at least qualitatively or semi-quantitatively.
Measuring the slope is very important, but it has to be considered, that only average values
over 1 meter slope length are measured. The position and the elevation of the knickpoints in
the rill must be recorded exactly and accounted in the analysis.
Using colour tracers, it became possible to record changes in flow velocity. This can be
caused for example by the overflow of a plunge pool, a process, that delivers a lot of water
and sediment in a short time. Without the knowledge of a change in flow velocity, the notice
of an increase in sediment concentration could cause a wrong conclusion.
In these experiments, 72 l of water are discharged with an intensity of 9 l min -1 into a rill, an
intensity also used in laboratory experiments by POLYAKOV & NEARING (2003). They
measured clearly higher sediment concentrations. That means, under other conditions, this
water quantity is sufficient to cause higher sediment loss. The Arnás catchment is still as
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