Présentations Colloques

Oral Presentation
8.04
Session 8.04: Isotopic and residence time tracers
Takeo Tsuchihara
Stable isotope-based investigation of infiltration effect of snow melting water on the groundwater in the large landslide block, Japan
One of the strongest trigger factors of land sliding is a rise of groundwater level caused by heavy rainfall and snow melting etc. Many landslide areas are distributed in snowy region of the northern part of Japan, and therefore, the landslide management in consideration of infiltration of snow melting water is highly important in these areas. In this study, stable isotopic compositions of oxygen and deuterium in rainwater, snow, stream water and groundwater were observed to investigate the infiltration effect of snow melting water on the groundwater in the large landslide block in Yamagata prefecture, northern part of Japan.**It can be found from the observations that the d-excess is different in rainwater and snow packs in this basin+ the mean values are 10.42 and 28.22 per mil, respectively. The high d-excess in snowfalls seems to arise from the increasing kinetic isotopic fractionation as relative humidity in the air above the ocean surface decreases in winter. This seasonal difference of d-excess in precipitation can be used to characterize the infiltration effect of snow melting water on the groundwater in the landslide block.**The d-excess in the stream water was increased by spring runoff in snowmelt season, and it decreased thereafter. Although the fluctuation range of d-excess in groundwater is smaller than in stream water, the d-excess in the groundwater of the landslide block was slightly increased in snowmelt season as well as in the stream water. It is thus deduced that the snow melting water has a certain effect on the groundwater in this landslide block and d-excess can be used as an index to evaluate an infiltration of snow melting water in landslide areas of snowy regions.**
Japan