Isotopic Analysis of Hydrologic Processes in a Small Semi-Arid Catchment
In an effort to better understand the dominant flow processes in semiarid systems, an experiment was conducted in a high instrumented 26 ha catchment in Idaho, USA. Snowmelt from deep snow drifts constitutes the main input into the basin. Subsurface geology consists of four basaltic layers underlying a soil layer - fractured basalt, semi-dense basalt, altered basalt and dense basalt. A total of 1600 water samples of precipitation, snowmelt, streamflow and groundwater were collected and analysed for 18O. Isotopic data indicate that snowmelt flow to the stream is mainly through the altered basalt zone, isotopically enriched snowmelt mixes sequentially with large columes of previously stored water. Tracer compositions indicated lack of active exchange of water between the geologic zones. Implications of findings for water balance modelling based on topography are discussed.