2003 Volume 33 Issue 3 Pages 125-136
The Kanto Plain has the largest groundwater basin. In this study, regional groundwater flow system in the major part of the plains are estimated from the three dimensional distribution of major dissolved ions, stable isotopes, and hydraulic heads.
Hydraulic heads gradually decrease from the surrounding part to the central part, in recent years. In the central part, minimal head zone is formed in depths from GL-100m to -300m. It is estimated the minimal head zone is made by the effect of groundwater pumping.
The distribution of hydraulic heads suggests the groundwater flows to the minimal head zone from the surrounding part.
On the other hands, from the distribution of chemical characteristics, groundwater zone with relatively low isotopic ratio is distributed in the central part, between Kazo lowland and Tokyo bay area. In the groundwater zone with low isotopic ratio, concentration of dissolved ions, especially Na+, HCO3- and Cl-, are higher than surrounding part. Low isotopic ratio zone has not found in the distribution of meteoric water, such as spring water and shallow groundwater collected from open well. Therefore, it is estimated the groundwater zone with low isotopic ratio had made by regional groundwater flow, not by recharge of meteoric water.
Groundwater with low isotopic ratio is distributed above the minimal head zone. This result shows the groundwater flow estimated from the distribution of recent hydraulic heads cannot make the groundwater zone with low isotopic ratio in the shallow depths of the central part. Therefore, the regional groundwater flow estimated from the distribution of stable isotopes represent the groundwater flow which has much natural state than the groundwater flow estimated from hydraulic heads.
