Abstract
In many practical applications, hydrogeologists are called upon to predict aquifer behaviour in areas devoid of pumping test data. Estimations of transmissivity may sometimes be made from specific capacity records, but in general storage parameters (specific yield and storativity) are not readily obtainable. Existing methods for estimating these parameters are few and inaccurate, especially for storativity (S). By returning to the basic definition of confined aquifer storage, a simple method has been developed for estimating S as a function of aquifer lithology and thickness alone. Variations in aquifer porosity (which are often difficult to quantify) are neglected in this formulation and numerical experiments have shown that the errors introduced by this assumption are negligible except for indurated aquifers of low compressibility (α < 10-10 ms2/kg). Porosity can be more easily determined for these aquifers than for unconsolidated aquifers of higher compressibility and a more accurate calculation of S can thus be made. This method has been tested against storativities derived from pumping test data for wells in the Altiplano of Bolivia and a good correlation between estimates and field values was found. The importance of obtaining good estimates for S is illustrated by reference to a typical problem encountered in a development project in the Altiplano, where the increased accuracy obtained using the new method (instead of older less rigorous methods) has beneficial consequences for the local community.
