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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Shear stress was calculated as follow:
τ = ρ g R S (Giménez and Govers, 2002) Eq. (7)
with ρ = fluid density [kg m -3 ], g = gravitational acceleration (9.81 m s -2 ), R = hydraulic
radius [m] and S = effective slope (sin(slope angle)).
The transport coefficient value was taken from the WEPP-database (Elliot et al., 1989). We
used the value of the soil that is most similar to the soil in the test area. In this case, the
location is Amarillo, the K t value is 0.0107 s 2 m 0.5 kg -0.5 .
For comparing the variability of the different parameters, we calculated first the average of
the relative measurement errors (RME) following the DIN 1319-1 (1995). This error is
defined as
xa
xr
RME = 100
Eq. (8)
x
r
with x a as measured value and x r as “correct” value, we used the mean of the measured values
as x r . The variance and the standard deviation are still in the unit of each parameter, therefore
the variances of different parameters are not comparable.
The RME describes the difference between the average value of all experiments and the
average values of one run. From our measuring values, we calculated the average value of
each run. The average of these “run-values” is the x r in Eq. (8), the average of each run is
presented by the x a . The given values in Table 4 are the average of the values of the 8 runs.
The RME would be much higher if we would calculate the RME between average values of
all 96 samples and the single, directly measured sample.
As second value for describing the variation, we calculated the empirical variation coefficient
EVC. It was calculated as follows:
standard
deviation
EVC =
average
Eq. (9)
The calculation for this factor is similar to the calculation of the RME values: We did not use
the mean standard deviation and the average of all samples, because of the different
conditions we calculated the average values for each run and averaged these results.
3 Results
Sediment concentrations at the MPs
We use a number-letter-system to identify our runs. The first number is the number of the
experiment, a or b means the first or the second run and the last number is the number of the
measuring point.
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