5th Swiss Geoscience Meeting, Geneva 2007
Soil erosion and rill development in dependence of
rainfall intensity
Catherine Berger*/**, Marcel Schulze***, Dirk H. Rieke-Zapp***, Hans
Kienholz*, Fritz Schlunegger***, Brian W. McArdell**
*Geographisches Institut der Universität Bern, Hallerstrasse 12, CH-3012 Bern
**Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft,
Zürcherstrasse 111, CH-8903 Birmensdorf (catherine.berger@wsl.ch)
***Institut für Geologie der Universität Bern, Baltzerstrasse 1-3, CH-3012 Bern
Soil erosion by water is one of the main factors causing land degradation and
has negative effects on the function of soils, leading to considerable damage in
the ecologic and economic sectors. The amount of soil erosion depends
strongly on the erosivity, which is a function of intensity and duration of the
rainfall (Boardman and Poesen 2006). According to the IPCC-report (2007), an
increase of heavy precipitation in the future is probable and is likely to give rise
to higher rates of soil erosion. The development of rills as a consequence of
surface runoff causes erosion, leads to increased soil losses and is therefore a
central factor for modelling scenarios and estimating the effect of expected
higher rainfall intensities.
The laboratory study presented herein had the objective to analyse the effect of
the rainfall intensity on soil erosion and development of rills. Similar studies but
with main interest on different slopes, roughnesses and slope shapes were
carried out for example by Gómez et al. (2003) and Rieke-Zapp & Nearing
(2005). A rainfall simulator at the Federal Institute for Forest, Snow and
Landscape (WSL) was used for the experiments and different rainfall intensities
with a constant total rainfall amount were applied on the test plots. The
intensities varied between 60 and 120 mm/h with a total rainfall amount of about
200 mm and rainfall durations between 2 and 4 hours. The slope of the soil
surface was fixed at 20 % and 11 experiments, where we primarily investigated
the influence of rainfall intensity, were carried out between spring and autumn
2006.
A wooden box (2 m x 1 m x 0.35 m) was constructed on a movable frame and
was outfitted with a subsurface drainage system at the bottom. The lower half of
the box was filled with sand and the upper part with a sieved Cambisol (5 %
clay, 60 % silt, 35 % sand; 5 % organic matter). The two layers were separated
by a geotextile and the soil was replaced after every experiment. Prior to the
experiments, the content of the box was saturated and drained twice for
establishing constant conditions and a consistent packing of the soil layer.
Discharge, sediment and drainage samples were taken at the outlet and at the
subsurface drainage tube during the experiments. A TDR-system recorded the
changes of the soil moisture and the state of the soil surface was analysed with
digital photogrammetry and a geographic information system. The rill networks,
their development and characteristic values such as rill density, energy and
stream order were calculated after the generation of digital terrain models.
5th Swiss Geoscience Meeting, Geneva 2007
The energy and evolution of the rill network was calculated and interpreted
according to the theory of the evolution of river drainage networks after
Rodríguez-Iturbe et al. (1992).
The results showed a positive, non-linear relation between soil erosion, rill
development and applied rainfall intensity. A threshold was found between 60
and 90 mm/h rainfall intensity: for rill networks formed above this threshold, rill
density as well as the energy of the entire system declined quickly in the first 30
minutes of the experiments and equilibrium was reached after approximately 60
minutes. The soil water content, discharge, drainage volume and transported
sediment all reached an equivalent equilibrium state as well.
The erosion processes were dominated at the beginning of the experiments by
the effects of the impacting raindrops and consequent splash erosion and
surface sealing. Subsequently, the formation and connection of depressions
resulted in a first network. Soil erosion was dominated thereafter by the surface
discharge and rills developed at intensities above the threshold value. The
higher the rainfall intensity the deeper incised and better formed were the rill
networks and the higher the total amount of erosion. Therefore we were able to
demonstrate that high erosion rates are linked to high rainfall intensities and the
formation of rill networks.
REFERENCES
Boardman, J. & Poesen, J. 2006. Soil Erosion in Europe. John Wiley & Sons
Ltd., Chichester.
Gómez, J.A., Darboux, F. & Nearing, M.A. 2003. Development and evolution of
rill networks under simulated rainfall. Water Resources Research, 29 (6), 1148.
IPCC 2007. Climate Change 2007: The Physical Science Basis, Summary for
Policymakers. In: Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change, 2007.
Rieke-Zapp, D.H. & Nearing, M.A. 2005. Slope Shape Effects on Erosion: A
Laboratory Study. Soil Science Society of America Journal, 69, 1463-1471.
Rodríguez-Iturbe, I., Rinaldo, A., Rigon, R., Bras, R.L., Marani, A. & IjjászVásquez, E. 1992. Energy Dissipation, Runoff Production, and the ThreeDimensional Structure of River Basins, Water Resources Research, 28 (4),
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