Hydrometric and tracer approaches to investigate rainfall-runoff processes in mountainous basins with different geologies

Hydrometric and tracer approaches have been applied to investigate the rainfall-runoff process in two headwater basins underlain by shale and granite. Four small basins were monitored; two in shale and two in granite. The rainfall peak was followed by the runoff peak in the shale basin, whereas peak runoff coincided with rainfall peak in the granite basin. Tensiometric data from hillslopes indicate that subsurface water percolated into the bedrock even during the rainstorm in the shale basin, whereas lateral saturated subsurface flow was often observed during heavy rainstorms in the granite basin. Considering the isotopic data from water, subsurface flow with relatively long residence times through the bedrock should be dominant so that the delayed runoff response was observed during the rainstorm in the shale basin, whereas lateral subsurface stormflow in the soil mantle should be dominant so that the quick response of runoff was observed during rainstorms in the granite basin.