The perched water table in the upper limestone aquifer of Malta

Abstract

The Maltese lslands are composed of two limestone aquifers separated by a clay aquiclude. In the lower limestone the water-table is controlled b y sea-level, whilst in the higher one - the Upper Coralline Limestone-it is perched. Water supply was derived solely from these underground sources until distillation commenced recently. Increasing demand led to the over-pumping of the sea-level watertable, with consequent increase in the salinity of the supply. Attention was therefore turned to the upper aquifer, and hydrogeological investigations were carried out. To determine the most satisfactory layout of galleries to drain the Upper Coralline areas, and to plan the development of underground storage, a comprehensive structural survey invoking over 1,500 boreholes was performed. A detailed study was made of the various types of limestone constituting the upper aquifer, with particular reference to specific yield and permeability. Their influence on the hydrologic characteristics and capacity of the underground reservoirs was appraised. Numerous sinkholes were discovered. Their presence suggested a possible source of leakage from basin structures, and led to their special in vestigation.