5th Swiss Geoscience Meeting, Geneva 2007
Can automatically derived maps of Dominant Runoff
Processes explain the magnitude of flood runoff in
August 2005?
Michael Margreth*, Felix Naef**
* Institut für Umweltingenieurwissenschaften, ETH Zürich, ETH Hönggerberg, CH-8093
Zürich (margreth@ifu.baug.ethz.ch)
**Institut für Umweltingenieurwissenschaften, ETH Zürich, ETH Hönggerberg, CH-8093
Zürich (naef@ifu.baug.ethz.ch)
In August 2005, many alpine catchments had an extreme flood. In spite of the
enormous amount of precipitation, the specific runoff of many steep catchments
was surprisingly low. Obviously, in these catchments a large part of the rain
could be stored for a short term. After saturation of these storage volumes,
runoff increased strongly. Can delayed reacting alpine catchments, susceptible
to this threshold behaviour be identified automatically in a GIS? When are the
large storage volumes exhausted?
To identify areas with large storage volumes, maps of dominant runoff
processes (DRP) are required. The decision scheme to determine the DRP
from Scherrer and Naef (2003) was implemented in a GIS, using high resolution
data of soils, geology, land use and topography (Schmocker-Fackel et al., 2007)
and applied successfully for the area of Kt Zurich (1730m2), covering a wide
range of topography, geology and flood producing precipitation regimes (Naef et
al., 2007).
In alpine areas, high resolution soil maps are often not available. To identify
delayed reacting steep alpine catchments, a DRP-map was produced
automatically for 100 swiss catchments, applying the decision scheme
mentioned above with low resolution geological and soil maps, available all over
the country. In a more time consuming method, the required hydrological soil
parameters like soil depth, grain size distribution and soil water regime were
derived in a higher resolution from geological, land use and topographical
information alone. This can be done with a reasonable accuracy in alpine
catchments, where soil formation depends strongly on topography and geology
(Margreth, 2004, Egli et al. 2004). This method was applied in the catchments
of Lütschine, Schächen, Allenbach and Minster. Results of these different
methods were compared and verified with manually derived process maps and
soil profile samples. They can be used to explain the different reactions
observed in these catchments and to get an idea about the reactions of the
rivers, when the storage capacities are exceeded.
REFERENCES
Naef, F., Margreth, M., Schmocker-Fackel, P., Scherrer, S. (2007): Automatisch
hergeleitete Abflussprozesskarten - ein neues Werkzeug zur Abschätzung von
Hochwasserabflüssen. Wasser, Energie, Luft (in press).
5th Swiss Geoscience Meeting, Geneva 2007
Scherrer, S. and Naef, F. (2003): A decision scheme to identify dominant flow
processes at the plot-scale for the evaluation of contributing areas at the
catchment-scale. Hydrological processes, 17(2): 391-401
Schmocker-Fackel, P., Naef, F., Scherrer, S. (2007): Identifying runoff
processes on the plot and catchment scale. Hydrology and Earth System
Sciences. http://www.hydrol-earth-syst-sci.net/11/891/2007/hess-11-8912007.pdf
Egli, M., Margreth, M., Vökt, U., Fitze, P., Tognina, G., Keller, F. (2005):
Modellierung von Bodentypen und Bodeneigenschaften im Oberengadin
(Schweiz) mit Hilfe eines Geographischen Informationssystems (GIS).
Geographica Helvetica, 2. S. 87 – 96.
Margreth, M. (2004): GIS- gestützte Modellierung der Bodentypen und anderen
Bodeneigenschaften im Berninatal. Diplomarbeit am Geographischen Institut
der Universität Zürich.