Prediction of runoff hydrographs in ungauged basins - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 230

Figure 10.3. Runoff generation mechanisms at the hillslope scale. (a) Infiltration excess near the Hydrological Open Air Laboratory (HOAL),
Austria (Photo: E. Murer); (b) saturation excess runoff in the Ebniter catchment, Austria (Photo: E. Zehe); (c) subsurface stormflow in the
Löhnersbach catchment, Austria (Photo: R. Kirnbauer); (d) runon infiltration in the HOAL (Photo: A. Eder).

vegetation. The former is controlled by the meteorological
conditions, the latter both by the meteorological conditions
(water vapour deficit) and by the stomatal resistance of the
plants. Water may become temporarily stored in microto-
pographic depressions or the canopy from which it will
evaporate, again controlled by the meteorological condi-
tions. Finally, part of the water may run off on the surface
or in the subsurface. These processes have a number of
characteristic time scales: the diurnal cycle of evaporation
in response to solar radiation fluctuations; a time scale
associated with the wetting/drying phase of days or weeks;
and the annual cycle of evaporation, again in response to
the seasonality of solar radiation. Over long time periods
the effects of the drying processes are embedded in the
seasonal variations of runoff (e.g., seasonal flow regime,
Chapter 6 ) and the long-term water balance (e.g., annual
runoff, Chapter 5 ). The entire spectrum of this variability is
reflected in the catchment

Surface runoff generated locally moves down the hill-
slopes towards the nearest river channel. The main controls
are the topographic slope, roughness and the microtopo-
graphic characteristics (e.g., tortuosity of the rills). In the
subsurface, water moves along the gradients of the
hydraulic potential, where macropore flow usually consti-
tutes the main part of the flow in the soil, while the matrix
contributes less. Due to the heterogeneity of the land
surface and that of the underlying subsurface soil medium,
the water movement over and through the hillslopes takes
place via a multiplicity of pathways, such as surface runoff,
subsurface stormflow and deep groundwater flow in either
porous media or fractured rocks ( Chapter 4 ). Depending
on the length, resistance and connectivity of the flow
paths, the runoff dynamics may differ vastly (Kollet and
Maxwell, 2006 ). This is illustrated in Figure 10.2 . The
Vermilion catchment in Illinois has shallow depths to the
aquifers and is tile drained. This is because, historically, ' sflowdurationcurve( Chapter 7 ).