Modelling of coastal karst aquifers for management support: a case study of Salento (Apulia, Italy)

Abstract

We are witnessing an increasing concentration of the human population in coastal areas on a global scale. This trend is associated with a growing demand for water, which is satisfied mainly by using local water resources and groundwater in particular. The phenomenon of seawater intrusion is therefore becoming a more serious problem for most coastal aquifers, whose water resources are obviously at risk of being subject to considerable degradation of quality and quantity. The problem is particularly relevant to karst aquifers, prevalent in the entire Mediterranean area and some Italian regions (Friuli, Sardinia, Sicily and Apulia). The purpose of this paper is to describe research that was performed to conceptualise and numerical model a coastal karst aquifer. This research is significant because of the importance of groundwater resources and the high intensity of changes made to well discharge in the absence of scienti cally based management when considering effects on quantity and quality. Salento (Apulia) was selected as a case study, and the changes that occurred over 80 years, starting from the beginning of its exploitation, were characterised. Complex acquisitions, together with climatic, hydrological, geological and agricultural data processing, served as the inputs for a numerical model of variable-density flow and transport created using MODFLOW and SEAWAT codes. In particular, groundwater flow under natural conditions was defined using a simulation in a steady-state condition. Through this simulation, it was possible to define the natural resource quantities and the salinity field, or the quality of groundwater that existed when withdrawals were null or negligible (during the 1930s). The transient simulations that we carried out were focused on the twenty years between 1980 and 1999, with the goal of quantifying the effects of the increased discharge used for drinking, industrial and especially irrigation purposes. The validation of the results was accurate due to the availability of high-quality historical piezometric data stemming from the IRPI-BA databases. The overall results demonstrated that the level of groundwater usage from Salento and the increasing discharge trend, due mainly to the global effect of individual water demand, will require a reversal of trends based on management criteria, defined on an aquifer scale and verified with a numerical model, whose potential can be shown by scientific expertise.