Hydrology and Earth System Sciences
www.hydrol-earth-syst-sci.net
1027-5606
1607-7938
11
2
2007
10.5194/hess-11-1047-2007
http://www.hydrol-earth-syst-sci.net/11/1047/2007/
http://www.hydrol-earth-syst-sci.net/11/1047/2007/hess-11-1047-2007.html
http://www.hydrol-earth-syst-sci.net/11/1047/2007/hess-11-1047-2007.pdf
1047
1063
2007-04-02
Rainfall threshold for hillslope outflow: an emergent property of flow pathway connectivity
P. Lehmann
peter.lehmann@epfl.ch
C. Hinz
G. McGrath
H. J. Tromp-van Meerveld
J. J. McDonnell
Institute of Terrestrial Ecology, Swiss Federal Institute of Technology, ETH Zurich, Switzerland
School of Earth and Geographical Sciences, The University of Western Australia, Crawley, Australia
Simon Fraser University, Department of Geography, Burnaby BC, Canada
School of Architecture, Civil and Environmental Engineering, EPFL Lausanne, Switzerland
Water Resources Section, Delft University of Technology, Delft, The Netherlands
now at: Laboratory of Soil and Environmental Physics, EPF Lausanne, Switzerland
on leave from: Dept. of Forest Engineering, Oregon State University, Corvallis, USA
Nonlinear relations between rain input and hillslope outflow are common
observations in hillslope hydrology field studies. In this paper we use
percolation theory to model the threshold relationship between rainfall
amount and outflow and show that this nonlinear relationship may arise from
simple linear processes at the smaller scale. When the rainfall amount
exceeds a threshold value, the underlying elements become connected and
water flows out of the base of the hillslope. The percolation approach shows
how random variations in storage capacity and connectivity at the small
spatial scale cause a threshold relationship between rainstorm amount and
hillslope outflow.
<br><br>
As a test case, we applied percolation theory to the well characterized
experimental hillslope at the Panola Mountain Research Watershed. Analysing
the measured rainstorm events and the subsurface stormflow with percolation
theory, we could determine the effect of bedrock permeability, spatial
distribution of soil properties and initial water content within the
hillslope. The measured variation in the relationship between rainstorm
amount and subsurface flow could be reproduced by modelling the initial
moisture deficit, the loss of free water to the bedrock, the limited size of
the system and the connectivity that is a function of bedrock topography and
existence of macropores. The values of the model parameters were in
agreement with measured values of soil depth distribution and water
saturation.
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