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

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Table 2 Constant parameters
Parameter Factor Value
Discharge intensity [ L min -1 ] 9
Setup Discharge quantity [L] 72
Discharge time [min] 8
Soil texture
Loamy sand
Organic matter [%] ~ 2.2
Land use
Arable land
Transport Coefficient K t [s 2 m 0.5 kg -0.5 ] 0.0107
Soil Vegetation cover [%] ~ 1
Rock fragment cover [%] ~ 2
Starting soil moisture [%] ~ 7.5
Grain density [g cm -3 ] 2.65
Dry bulk density [g cm -3 ] 1.68
Average precipitation [mm a -1 ] 380
Climate
Average annual temperature [°C] 19.2
Evapotranspiration rate [mm a -1 ] 1084
Characterisation
Semi arid
2.2 Rill experiment
The rill experiment consisted of two runs: in the first run the rill was tested under dry
conditions; in a second run, 15 min later, the same rill was tested under wet conditions,
therefore the influence of the initial soil moisture could be considered.
For each run, a motor driven pump was used to maintain a constant discharge of 9 L min -1 for
8 minutes, resulting in a total water flow of 72 L (Wirtz et al., 2010, Wirtz et al., 2012). In the
used range of water quantity and pressure the fluctuations were very low so we can assume
that the inflow was stable.
The flow velocity within the rill was characterized by the travel time of the waterfront and of
two colour tracers (food colourings (E 124 red and E 13 blue started at 3 and 6 minutes after
the start of the experiment) measured for every meter using a chronograph. By means of this
procedure, three velocity curves with the maximum flow velocities were recorded and
changes in flow dynamics could be detected. Following Govers (1992b) we assumed that the
mean flow velocity is reached, where the waterfront reaches 80 – 90 % of its maximum width.
In our experiments, the difference between the front and this point could not easily be
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