Abstract
In Japan, the artificial forestation has been believed to increase the groundwater recharge and widely applied for the purpose of groundwater resources management. However, the quantitative evaluation of effect of the artificial forestation on the groundwater recharge rate is not well studied. In this study, to understand the effect of groundwater recharge rate by artificial forestation, groundwater recharge rate were compared by using the Displacement Flow Model for stable isotope ratio in rain and soil water of the selected forest and grassland catchments, the western foot of Mt. Aso, Kumamoto prefecture, south-west Japan. In both catchments, stable isotope ratio of soil water samples were plotted on the summer LMWL in a δ diagram. This means that the main recharge occurred during the summer season and the influence of isotopic fractionation was small.
The estimated mean annual recharge rates by DFM were 1493 mm/y and 1920 mm/y in forest and grassland catchments, respectively. As a result, this study shows the groundwater recharge rate is about 30 % larger for the grassland catchments than that for the forest catchment under the similar geological and hydrological condition. This result suggests the effect of seepage characteristics of the surface soil of the study area.
