Experimental investigation of runoff generation processes at the Dreisam catchment
In recent years different experimental investigations were carried out in the Dreisam catchment
(258 km2) with its different sized sub-basins (0.1-52 km2). Tracer investigations allowed quantifying
the contribution of different runoff components at the event and seasonal time scale. In particular
the significance of groundwater for stream flow generation during different hydrological
circumstances was quantified. The large importance of shallow groundwater became obvious
in the mountainous test site. The use of environmental isotopes (18O, 2H and 3H) and CFCs
(F-11, F-12 and F-113) allowed to date the age of different runoff components. The quantification
of the amount and the age of different runoff components is extremely important to understand the
functioning of the hydrological system and, consequently, for the development for ecosystems.

Key publications:

  • Uhlenbrook S., Leibundgut Ch., Maloszewski P., 2000: Natural tracers for investigating residence
    times, runoff components and validation of a rainfall-runoff model. In: Dassargues A., 2000: Tracers
    and Modeling in Hydrogeology. IAHS-Pub. No. 262, 465-472.

  • Uhlenbrook S., Frey M., Leibundgut Ch., Maloszewski P., 2002: Residence time based hydrograph
    separations in a meso-scale mountainous basin at event and seasonal time scales.
    Water Resources Research, 38, 6, 1-14.
Hydrograph separations in a meso-scale mountainous basin at event
and seasonal time scales

Stefan Uhlenbrook

The spatial and temporal (event and seasonal time scale) variability of major runoff components
in the mountainous Brugga basin (Black Forest, Germany) were examined. The meso-scale (40 km2)
study basin represented an extraordinary challenge as comparable studies have been undertaken
mainly in smaller headwater basins. Discharge data, tracer concentrations of 18O, 3H, CFCs,
dissolved silica and major anions and cations were analyzed during single events and over a period
of three years. Three main runoff components were defined: event water with a residence time of
several hours to a few days contributed up to 50% during flood peaks, quantified by a classical
hydrograph separation technique using 18O.

However, this component is of minor importance for longer periods, comprising about 11.1% of
total runoff as estimated for the period August 1995-April 1998. The other two flow components
originated from shallow and deep ground water. Source areas for these are the upper drift and
debris cover for the shallow ground water and the deeper drift, weathering zone and hard rock
aquifer for the deep ground water. Mean residence times ranged from 28 to 36 months based on
18O data for the shallow ground water, and from 6 to 9 years based on 3H and CFC data for the
deep ground water.
The importance of the upper drift and debris cover of the slopes for runoff generation at the test
site was clearly demonstrated at the seasonal time scale, showing a contribution of 69.4% based
on a mixing model with a monthly time step. The deep ground water contribution was 19.5%.
With this information , a conceptual model of runoff generation for the study site was constructed.

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