EROSION PROCESSES IN A SMALL CATCHMENT IN THE UPPER LUSATIA REGION INDUCED
BY HEAVY RAIN EVENTS
Matthias Kaendler, Christina Seidler
International Graduate School Zittau, Markt 23, D-02763 Zittau, Germany
e-mails: kaendler@ihi-zittau, seidler@ihi-zittau.de
The European Water Framework Directive (WFD, 2000) aims at maintaining and improving the
aquatic environment in the Community. The solution of related problems requires detailed knowledge
of the meteorological, hydrological and geomorphological conditions and processes. In agricultural
used regions erosion and suspended load play an important role. Until now there is a lack of
knowledge about the complicated process-chain of particle displacement, transport pathways and
suspended load as well as the effect of suspended particles on water organisms. The predicted
climate change leads to more extremes, including higher rainfall intensities, resulting in a worsening of
the problem of erosion and sediment load in the rivers. The investigation in the Landwasser catchment
aims at the identification, analysis and quantification of abovementioned processes and problems. The
catchment (28 km²) is part of the Nysa-basin. It is mainly agriculturally (70 %) used with partly steep
slopes, and the river bed is strongly influenced by human activities (urban areas 20 %). The region is
covered by silty soils with high erosion potential.
Suspended load and turbidity are measured at the catchment outlet. To detect the dynamic of
suspended particle transport, an automatic water sampler was installed. Samples are taken controlled
by discharge (e.g. every 500m³). Thus, it is possible to find out the changes during a flood wave.
Additionally samples are taken from selected tributaries and drain outlets. Afterwards the samples are
analyzed in the lab. All meteorological elements are recorded hourly. Precipitation is measured in 5
minutes time step.
Flow pathways (overland flow) were identified with the help of the digital elevation model, and areas
with similar runoff components were defined with the WBS-FLAB Model (Peschke et al., 1999). Areas
with surface runoff are the risk areas of erosion processes (Fig. 1).
Figure 1: Map of runoff components and flow pathways in the Landwasser catchment
Areas with low infiltration capacity are able to produce surface runoff and erosion. These are mainly
the yellow zones in Figure 1. Particularly the fields with steep and moderate slopes close to flow
pathways deliver particles to the brooks and rivers. The erosion risk is big during periods with partly
covered soils and heavy rainfall events.
The analysis of the heavy rain event from 14th/15th May 2007 shows that the surface runoff led to soil
loss and high concentration of suspended load in the river. The maximum value of 38 g/l occurred one
hour after the discharge maximum. The first flood wave transported 200 tons of suspended particles
out of the catchment. Concentration of Chloride and Conductivity are connected as expected. With
increasing water level chloride seemed to be diluted.
Nitrate concentration is delayed to the suspended sediment concentration maximum, because it is
released by agricultural drainage systems.
Heavy metals (e.g. copper) reached their concentration maximum before all other components. They
are removed from streets and urban areas close to the river.
The analysis of further rain events showed, that some parameters change their relations during the
vegetation period (e.g. nitrate and suspended load), because of plant uptake and increasing soil
coverage. Further investigations to gain detailed knowledge of the transport processes within the
catchment are necessary.
Soil loss and particle concentration in the river can be reduced by different measures, such as yearround soil cover through appropriate management strategies (e.g. catch cropping, direct sowing,
conservation tillage), through land use changes (e.g. conversion of farmland to grassland or forest), or
by buffer strips (Kaendler et al., 2008) and hedges close to the river.
It is necessary to identify the real risk areas to quantify the amount of transported mass and the impact
on the aquatic organisms.
Keywords: Erosion, water quality
References
Kaendler, M., I. Baerlund, M. Puustinen, C. Seidler (2008): Capacities of modelling to assess buffer
strip efficiency to reduce soil loss during heavy rainfall events. In: Strelcova, K., C. Matyas, A. Kleidon,
M. Lapin, F. Matejka., J. Skvarenina, J. Holecy (eds.): Bioclimatology and Natural Hazards, Springer,
Geosciences (in print).
Peschke, G., C. Etzenberg, G. Mueller, J. Toepfer & S. Zimmermann (1999): Runoff generation
regionalization - analysis and a possible approach to a solution. In: Diekkrueger, B., M. Kirkby & U.
Schroeder (eds.): Regionalization in Hydrology. Proceed. of the Braunschweig Conf. March 1997.
IAHS Publ. No. 254, 147-156.
WFD (2000): Directive 200/60/EC of the European parliament and of the Council of 23 October 2000.
Official Journal of the European Communities. L 327