Abstract
The results obtained through the further study on the subject are described hereunder.
An unconfied aquifer model as shown in Fig. 1 has been clarified to be a depletion model of exponential function type as given by the following equation;h (t)=h(O)e-(α/λ)/t (7).
A slope of depletion part of semilogarithmic time-series plot of groundwater head, A, is defined to beA=α/λ (8).
Thus the real depletion coefficient, α, can be known when the specific yield, λ, becomes clear.
The specific yield of a basin can be known through a proper pumping test. Otherwise an approximation may be made by an apparent depletion coefficient, A, and rainfall depth within a period. The manner of approximation are given in the equations (9) to (15).
When the α and λ are properly defined a recharge other than from rainfall may be evaluated.
Some of representative models under various hydrogeological conditions are illustrated in Fig. 3. One of time-series plots of observed and simulated hydrographs made for a verification purpose of a model is given in Fig. 4.
Excluding major exceptions, the α and λ concentrate an order of n×10-4 day-1 and several percents respectively.
Two kinds of recharge structure are described through the model adopted to a coral island that there are a slow structure for usual input and a rapid one for input in high intensity.
