The maximum quantity of groundwater which can be withdrawn from a particular groundwater basin is limited by the danger of land subsidence. The author proposes a simple new method for calculating this maximum value on the basis of empirical data.
First of all, the average discharge (m
3/day) of wells of a given groundwater basin is calculated from the list of deep well discharge. Most deep wells may be regarded as in operation half of the time, so that half of the average discharge is assumed to be mean discharge Q (l/sec) in practice. When the discharge per unit time and unit area Z (m
3/day/km
2) corresponding to Q is read on the regression line of the spring area in the Z-Q-n/A diagram, Z is the safe unit area discharge of the particular groundwater basin. The product of this value of Z and A (km
2), which is the presumed continuous area of the groundwater basin determined from a hydrogeological survey, is the safe yield of the groundwater basin (m
3/day).
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