Abstract
By means of three isotope tracer techniques, proportion of direct runoff and characters of groundwater runoff were studied in the Iwami River drainage during a high runoff period for about 3 days, caused by a heavy rainfall of 85 mm for 17 hours. The proportion of direct runoff is 15% or less of the total runoff caused by the rainfall, while 65% of river water at the peak of runoff. Differences observed in the runoff manners among 18O, 2H, and 3H are interpreted as a result of preferential runoff of previous precipitations stored in some unsaturated zone above the saturated groundwater zone. Cl- content is not conservative as a tracer to study runoff mechanisms.
