A progressive rise in groundwater level has been reported in several major cities in the world. The principal cause of the rise is the reduction of groundwater abstraction which is mainly controlled by groundwater management through economic activities and governmental regulations for groundwater use. Another important cause of the rise is leakage from water supply networks.
In central Tokyo, over the last thirty years, the groundwater level has risen more than 30 m. In addition, about 380 thousand tons of drinking water was estimated to have leaked per day from water mains from 1994 to 1996, and this value is much larger than the volume of rainfall infiltration into the ground.
A rise in groundwater level gives us benefits such as rebirth of dried springs, recovery of polluted river water, appearance of aquatic animals and plants, securement of emergency water, etc. However, the rise possibly produces negative effects on our daily life environment, traffic facilities, underground foundation and structures. Actually, flooding of building basements, leakage into sewers and subway tunnels, increase in hydrostatic pressures on basement structures, reduction of slope stability and so on caused by the rise have been reported in several major cities.
In most cases, the rise in groundwater level would lead to unexpected situations, because cities have rapidly developed and spread when groundwater level was so deeper than that in the present days. We need to establish new groundwater control policy and action schemes against the rise in water level to diminish risks and create better environment.
