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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Do deterministic sediment detachment and transport equations adequately represent the
processes interactions in eroding rills? An experimental field study.
Stefan Wirtz • Manuel Seeger • Alexander Remke • René Wengel • Jean-Frank Wagner •
Johannes B. Ries
Dep. of Physical Geography, Trier University
Abstract
This paper tackles two main questions by linking observations, determination of hydraulic
parameters and measurement of sediment transport with the formulae used in soil erosion
models. First, do constant shear stress values in different rills with constant soil parameters
result in the same soil detachment values? Secondly, deterministic soil erosion models make
the assumption that there is a relationship (often further assumed to be linear) between shear
stress and soil detachment; is this suitable for representing real erosion process combinations
in natural rills? Following most process based deterministic soil erosion models, derived
hydraulic and erosion parameters should be similar. However, the results from the different
experiments showed clear differences in sediment concentration, transport rates and other
measured as well as calculated values. In contrast to our experimental results, a model
simulation would produce erosion parameters with low variations, represented by the relative
measurement error and the empirical variation coefficient. This reveals the general problems
of using process based deterministic models for erosion in shallow rills. While soil erosion
models simulate the processes resulting from the shear forces of flowing water on the soil
surface, other processes like side wall failure, headcut retreat and plunge pool dynamics are
not taken into account. Our results suggested that these other processes may contribute
substantially to rill erosion processes. The results of this study strongly suggested that the
model concept of most physical based soil erosion models is inadequate for modeling rill
erosion processes. Measured total rill erosion rates were the sum of erosion rates caused by a
combination of different soil erosion processes with different spatial and temporal
distribution. This combination cannot be described by a single equation.
Keywords Experimental field work • Process based soil erosion model • Rill erosion • Soil
erosion
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