Hydrograph separation in a mountainous catchment - combining hydrochemicaland isotopic tracers

Runoff components of the Zastler catchment (18.4 km(2), southern Black Fore st, Germany) were analysed with hydrograph separations using stable oxygen isotopes and dissolved silica. It was shown that event water and components with low silica contributed only small amounts to total runoff. In additio n, comparison of the two-component hydrograph separations showed that the l ow-silica components are generated by both event water and pre-event water fractions, depending on the state of the system. A modified three-component hydrograph separation method was introduced usin g dissolved silica and O-18. During storm events an interaction of three ru noff components having distinct silica concentrations could be shown. Based on the geological and geomorphological genesis of the study site, it was a ppropriate to assign (i) the low silica component to the riparian zones and impermeable areas, (ii) the medium silica component to the periglacial deb ris cover and (iii) the high silica component to the crystalline detritus a nd crystalline hard rock. Exact quantification of the runoff components remained difficult. However, runoff components with medium silica concentrations reacted very sensitivel y and intensely. The contribution of this component to total runoff is comp aratively large. This shows the important role of the periglacial debris to runoff generation of the study site and emphasizes the importance of runof f generation processes occurring in this reservoir. Copyright (C) 2000 John Wiley & Sons, Ltd.