No abstract

Production of storm runoff in highly responsive catchments is not well understood. We report in these papers a comprehensive set of hydrometric and natural tracer data for rainfall, soil water, and streamflow for catchments in the Tawhai State Forest, Westland, New Zealand, which reveal some of the important runoff processes. The catchments are small (< 4 ha), with short (< 300 m) steep (average 34°) slopes and thin (< 1 m) permeable soils. Long‐term (1977–1980) weekly observations of oxygen 18, electrical conductivity, and chloride in the stream, groundwater, and rain in the main study catchment indicate that catchment outflow reflects a well‐mixed reservoir with a mean residence time of approximately 4 months. A preliminary storm hydrograph separation using oxygen 18 (for a storm hydrograph exceeded by only 22% of events since 1979) indicates that only 3% of storm runoff could be considered “new” (i.e., current storm) water. Rapid subsurface flow, such as macropore flow, of new water therefore cannot explain streamflow response in the study area. More detailed hydrograph separation studies on throughflow as well as streamflow are described in parts 2 (M. G. Sklash et. al., this issue) and 3 (M. G. Sklash et. al., unpublished manuscript, 1986).

No abstract

Previous hydrometric and dye tracer studies in Maimai 8, a highly responsive catchment in the Tawhai State Forest, Westland, New Zealand, suggest that storm runoff generation is by rapid transmission of “new” (current storm rain) water to the stream via macropores. We used hydrometric and natural tracer (oxygen 18, deuterium, electrical conductivity, chloride) observations in two first‐ and one second‐order stream and in six throughflow pits, to evaluate the roles of “old” (stored) and new water during three storm events (return periods from 4 weeks to 3 months) in September 1983. New water contributions were small (<25% of the hydrograph volume) and could be accounted for by saturation overland flow. Hillslope response varied areally but all sites issued old water‐dominated throughflow. Ridge top sites had larger new water contributions (∼ 30–40%) than valley sites (< 10%). Macropore flow of new water therefore cannot explain streamflow or throughflow response in the Maimai catchments.