Hydrogeology and subjects caused by recovering of groundwater level in Tokyo.

Abstract

The plain area in the east part of Tokyo, Musashino Terrace and Shitamachi Lowland, is underlain by Quaternary thick sediments. These sediments are divided stratigraphically into two groups, the lower is the Kitatama Formation and the upper the Tokyo Formation. The general strike of the Formations tends NNW-SSE with a very low dip to the northeast. Upper layers of the Tokyo Formation are mainly composed of silt, sand and gravel, forming the aquifer system of artesian groundwater. According to the distribution of Tritium ratio in the groundwater, which of Musashino Terrace has mainly supplied from the surface water of the Tama River.Withdrawal groundwater from these aquifers has caused the lowering of groundwater level and the land subsidence all over the plain. The lowering of groundwater level and the land subsidence, however, which have continued half a century, rapidly taken favorable turns during recent about ten years due to restrictions of groundwater withdrawal.Recovering of groundwater level has not only brought about the favorable turn of the land subsidence, but also decreasing the spout of oxygen deficient air through water wells and the cracks of basements at the time of air pressure change or pnuematic work in the underground.It also has advanced the secondary storage of natural water soluble gas, which has reserved originally in the deep layers, the Kazusa Group, into gravel layers beneath the Yurakucho Formation.

Multivariate analysis of trace elements in shallow groundwater in Fuchu in western Tokyo Metropolis, Japan

“…1). The study site is located about 3.5 km from Tama River and 35 km from Kanto Mountains in Kanagawa prefecture (Endo and Ishii 1984;Endo 1992;Imaizumi et al 2000). The groundwater is therefore expected to be influenced by relatively high-DO content water from those water sources.…”

“…The elevation of Fuchu is about 30-80 m above the mean sea level. Groundwater in shallow confined aquifers is originated from the Kanto Mountains in Kanagawa prefecture and Tama River (Endo and Ishii 1984;Endo 1992;Imaizumi et al 2000). Stratigraphy of the study area consists of two groups: the upper Tokyo group and the lower Kazusa group (Endo 1992).…”