Tracers for runoff generation studies in a Mediterranean region: Comparison of different scales

Natural and artificial tracers were used to investigate runoff generation processes at different spatial scales in steep carbonate hillslopes of the Judaean Mountains, West Bank and Israel. At the 180-m² plot scale, artificial tracers, added to the waters of a two-day sprinkling experiment, enabled a two-component hydrograph separation emphasizing the important role of shallow surface depressions, soil cover and subsoil morphology in runoff generation. At the hillslope scale, the contents of magnesium and calcium in overland flow followed the large scatter found in the precipitation of three storm events. Tracer concentrations in subsurface sources remained rather constant with only one exception. In the 2.6 km² small catchment, a group of samples with low mineral content indicated dilution during storm events. During one event the temporal dynamics of deuterium provided independent evidence for storm water impact both at the hillslope and the small catchment scale. It is hypothesized that most of the hillslopes investigated act as a flood generating zone rather than as an area of pronounced infiltration and recharge to the underlying regional karst aquifer, at least during high magnitude rainfall.