HYDROGEOLOGICAL WATER BUDGET OF THE KARST AQUIFER FEEDING PERTUSO SPRING (CENTRAL ITALY)

The evaluation of the active recharge of karst aquifers is an important tool to estimate the groundwater resource availability in these complex hydrogeological systems, characterized by spatial and temporal variability of many hydrogeological factors, involved in groundwater flow. As a matter of fact, the rate of recharge is a key aspect for sustainable exploitation and management of these groundwater resources, as they represent one of the most important fresh-water supplies for human life and economic activities. This paper presents the results of the inverse hydrogeological water budget method application in the karst aquifer feeding Pertuso Spring, Central Italy, to evaluate the average annual groundwater recharge (i.e. the effective infiltration), supported by an open source GIS. This carbonate aquifer is one of the most important of Central Italy and Pertuso Spring is the main outlet of this karst system with an average rate of about 1.7 m3/s. The study area lies in the Upper Valley of the Aniene River, in the south-east part of Latium Region, and is spread for about 50 km2. Calculation of the effective infiltration was based on mean annual rainfall data, collected over 20 years (1992-2012), evapotranspiration and on hydrogeological settings of outcropping rocks, used for setting up potential infiltration coefficients. The inverse hydrogeological water balance has been applied to the study area, discretized in grid cells (EFQ), 6.25 Ha each one. The results of the inverse hydrogeological water balance method applied to the karst aquifer feeding Pertuso Spring show an annual recharge of about 45 Mm3/year. The effective infiltration map shows that the highest values are related to the presence of karstified Cretaceous limestone, mainly outcropping in the north-east part of the basin. On the contrary, lower values of effective infiltration are generally due to the lower permeability, which characterizes the rest of the area (Triassic crystal dolomites, pudding stones and conglomerates). Results show that the annual active recharge of this karst aquifer (45 Mm3/year) is greater than the depletion volume of water coming from Pertuso Spring (25 Mm3/year). The evaluation of the active recharge is a useful tool to identify the priority protection measures for sustainable land use planning and groundwater management in the study area