KARST AQUIFER EMPTING DURING DRY PERIODS AND DROUGHTS

Karst springs are among the most important water supply sources for a large part of Mediterranean regions, and in particular in Southern Italy. Their hydrological regimes depend both on the climate characteristics, and on the geological layouts and karst features of aquifers. During the long Mediterranean dry summer, generally, only karst springs are able to provide fresh and high quality water, without pumping from wells. These characteristics are fundamental in the analyzed areas, where the recession limb of the karst spring hydrograph allows the water supply during the long dry summer, an important aspect during the development of civilization since antiquity.

To describe the aquifer behaviour during the dry seasons, we focused the analyses on the recession limb of the spring hydrographs. This topic is well-known in karst hydrogeology, as many authors have proposed some analytical models to simulate the recession limb of the spring hydrographs. In this study, a water filled tank is emptied by a hole, and analytical formula are computed in relation to the geometry of the tank and to the type of the hole, using different emptying physical laws. This simple model allows to control the geometry and hydraulic conditions of the reservoir, which are generally unknown during the emptying of the real karst aquifer, providing useful details on the karst system behaviour. The spring hydrograph recession has been analyzed for several years, thanks to detailed discharge measurements of some main karst spring of Picentini mountains, which supply millions of people in Southern Italy.

Based on physical tank-reservoir model, some analytical hydrogeological features of the karst aquifers are deducted, and aquifer behaviour during drought is also discussed.