THE USE OF STABLE ISOTOPES OF WATER (D AND O-18) IN HYDROLOGICAL STUDIES IN THE JONKERSHOEK VALLEY

We used stable isotopes of water in rainfall and streams in the Jonker shoek Valley to determine the relative contribution of new water (i.e. rain) during stormflow conditions. We found significant differences b etween rain and stream isotopic signatures which facilitated the use o f a mass balance equation to calculate the components of stormflow. An alyses indicated that < 5% of the stormflow comprised direct runoff. T his suggests that the rapid response of these streams to rainfall is m ainly due to displaced groundwater.