Runoff characteristics in a small mountain basin analyzed by the use of hydrogen and oxygen stable isotopes

Abstract

The hydrograph of a small drainage basin was separated into the components of direct runoff, soil water runoff, and ground water runoff, by a method using a stable isotope (¹⁸O and deuterium) to analyze its hydrological characteristics. It shows that the direct runoff consists of rainwater during the event, soil water runoff originating from the latest rainwater before the event, and groundwater runoff is a perfect mixture of rainwater brought to the catchment throughout the year. If these water masses constitute a triangle on a δD–δ¹⁸O diagram, they are independent of each other, and the separation gives a unique result. A comparison of the above results with the hydrograph separation in terms of the response time using a tank model led to an estimation of the flow path and dynamics of each runoff component. This study investigates the mixing process involved with these runoff components and, further, identifies physical properties to be observed in the field to provide for a more detailed analysis of the runoff process.