Abstract
Unit area discharge of groundwater, Z (m3/day/km2) can be expressed by the following equation,
Z=n/AQ
where Q is the average discharge (l/sec) of well or spring, A is the area (km2) of the surrounding terrain having the same hydro-geologic condition at the well site. n/A is called the coefficient of well distribution or of spring distribution.
This paper deals with the calculation of Z values for Tokai and Chugoku-Shikoku districts with the amount of free groundwater and with that of artesian groundwater. The Z values of artesian groundwater in those districts were plotted on the inter-section chart, Z-Q-n/A diagram, with reference to several well-known land subsidence area. On the diagram, the regression equation based on the method of least squares for 10 sites in the spring area is as follows:
logZ=0.772logQ+2.357
and that for 4 sites in the land subsidence area is
logZ=0.890logQ+2.617
The value of n/A in the land subsidence area was high as 2.5-4. This result suggests that the land subsidence might be due to the overdraft of artesian groundwater rather than that of free groundwater.
