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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Fig. 11 Relationship between transport rate and transport capacity vs. runoff. The equilibrium
line is shown
Variability in soil erosion measurements
The input parameters for calculating shear stress showed average RME values below 20%:
hydraulic radius with 16.4%, slope with 14.7% and liquid density with 0.7%. The calculated
shear stress values were also similar; the variability was 28.6% when liquid density with
sediment concentration considered was used and 28% if the liquid density of clear water was
assumed. In models, a commonly-used idea is that there is a linear relation between shear
stress and soil detachment volumes. This means that the variability of soil loss parameters
should also be in the same order of magnitude. For transport and detachment rate, input
parameters are still flow velocity and sediment concentration. Flow velocity showed a low
variability of 10.2%. On the other hand sediment concentration (70.5%), transport rate
(81.7%) and detachment rate (67.5%) showed very high variability, all values being over
60%. This variation in values contrasts with the approach used in models. In a model
simulation the variations of the input parameters and the soil loss parameters would be
similar. This means that in this case, there was no simple linear relation between shear stress
and soil detachment.
The results of the research reported by Govers (1991), Liu et al. (1996), Nearing (1998, 1999
a), Risse et al. (1993), Ruttiman et al. (1995), Wendt et al. (1986) and Zhang et al. (1996)
underscore the problems. Nearing (1998) tested the variability between replicated soil erosion
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