Hydrogeology of the Musashino Terrace

Abstract

In the whole area of Musashino district, the demand for groundwater, as the source of service water and industrial water, has been increasing year by year, and in some quarters of this district we have already found a serious matter. Recently, therefore, the conservation and the reasonable development of groundwater have come to be considered as one of the natural resources.
Meanwhile, as the groundwater supply and preservation conditions are closely related with the geological structure of aquifers, the investigation of subterranean geology of the area concerned should be done first, so as to realize the aim mentioned above.
As a result of this investigation, I have been able to arrive at a solution to this problem, which is as follows.
A. Concerning the hydrogeological structure of the area.
1. According to the deep well boring datum in this area, eight main aquifers are distinguishable. In this paper, I call them A₁, A₂, .... A₈ (lower to upper).
2. The lower planes of each aquifers indicate undulating features and valleys found on them go from west or south-west to north-east of Musashino district with a low pitched dip.
3. Horizontal distributions of each aquifers show arciform which open toward northeast (upper aquifers are situated at north-east side).
4. The stratigraphical positions of aquifers which have been developed, vary in different localities. Therefore, it is difficult to decide easily that excessive utilization of groundwater at upper area has influence on lower area.
B. Concerning the mechanism of the groundwater preservation.
1. Pressure surface of groundwater is closely related to the geological structure of aquifers. As a whole, in the western area, it dips toward east and in the eastern, toward north-east.
2. Also, the type of water level movement is closely related to the stratigraphical position and locality of aquifers.
3. In general, capacity of discharge (transmissibility, specific capacity) is large at the valleys mentioned above.
C. Concerning the sources of groundwater and the mechanism of supply.
1. The main sources of the groundwater are river flow (Tamagawa, Akigawa, Asakawa, etc.) and unconfined groundwater of this area.
2. The increase and decrease of supply, changes in proportion to utilization of groundwater.
In this area, quantity of supply is estimated at about 7080 % of the utilization.