多孔性パイプを使用した地下水流速の定点電気測定法

抄録

Groundwater is a very important source of irrigation and city, water supply. Scientific researches of available discharge of groundwater are indispensable in their exploitation. The velocity and direction of groundwater stream are very difficult to fathom. The methods hitherto used for this purpose are as follows:
(i) measurement of the gradient of groundwater level using pipes or wells;
(ii) tracing of groundwater labeled with salt, fluorescent substances, or radioisotope solution;
(iii) electrical or seismic exploration.
The method (ii) is very common but several hours are required even in the measurement at only one point.
The author studied a new method of the measurement of the velocity and direction of groundwater stream by means of porous pipes driven in the ground, and found that this method could save much time.
(a) The relation between U₂ (velocity of stream in the inside of the pipe) and U₂ (that in the outside of the pipe) was analyzed as follows:
U₂=U₁2_k2/k₁+k₂=2U (k₂≥k₁)
k₂=equivalent of the coefficient of permeability corresponding to the seepage through the holes of the pipe,
k₁=coefficient of permeability of the ground.
(b) The direction of groundwater stream in the inside of the pipe is perfectly coincident with that in the outside of the pipe.
(c) The velocity of groundwater stream is obtained by the measurement as is indicated in Fig. 4.
R₁, R₂: fixed electric resistances;
R₃, R₄, R₅: variable electric resistances;
E₁, E₂: sources of electricity;
S₁, S₂: switches;
A: source of heat;
B: pickup (thermister);
Am: ammeter;
G: galvanometer.
The velocity is calculated by the formula
U1=KL/2T
U₁: velocity of groundwater stream;
L: distance from source of heat to thermister;
T: time of the movement of heated water from source of heat to thermister;
K: coefficient.