A STUDY ON THE RECESSION OF UNCONFINED ACQUIFERS

Abstract

The dependence of the recession of the ground water levels and the ground water discharge upon the initial state of the aquifer is examined for deep unconfined aquifers. It is shown that only in the early stages of the recession does the initial state exert a limited influence on the recession. An estimate of the upper limit of the time t ₀ for which for t > t ₀ the recession becomes effectively independent of the initial state of the aquifer, valid for physically realistic initial states can be gained from inequalities (11) and (12a) and equation (16). t ₀ depends essentially on the parameters of the aquifer and it is estimated that for useful aquifers t ₀ can not be expected to exceed one month in relatively adverse cases. This explains why empirical recessions often are found to be consistent, of an exponential form.