Combination of tracer techniques and numerical simulations to evaluate the groundwater capture zone

The groundwater flow system and capture zone were evaluated using the combination of stable isotopes, continuous measurements of groundwater seepage rate, and numerical simulations by a 2-D unsaturated-saturated three-layer model. The [dgr ]18O of the precipitation was used as a tracer to detect the capture zone. The depth of the groundwater which discharges near the lake shore is estimated to be deeper than 100 m below the surface even though the clay layer exists from a depth of 10 to 20 m below the surface. The combination of tracer methods and numerical simulations enabled us to understand the groundwater flow system and the capture zone of the groundwater in the Lake Biwa basin.