Abstract
Hydrochemical observations of discharge waters have been carried out from subsurface drainages and spring in the Takisaka landslide area, Fukushima Prefecture, Japan. The samples have been collected from the Sodenosawa drainage tunnel, collecting wells, and the Matsuzaka spring in the landslide area. The main objectives of this study are to identify the change in dissolved components after rainfalls and to access the relation in term of landslide stability. On the basis of the major solutes in groundwater and geology of parent rocks, groundwaters in this area are chemically classified into two types . One is the enriched Na-SO4 type derived from the mudstone unit and the other is Na-HCO3 type derived from the arkose unit that is close to the slip surface. The corrected HCO3- concentrations with that of the Matsuzaka spring water are almost constant among the groundwaters . The Sodenosawa drainage tunnel discharges large volumes of Na-HCO3 type groundwater during a few days after the >30mm/day rainfalls. These indicate that discharge of Na-HCO3 type groundwater is closely related to the stability of the landslide mass.
