Modellazione numerica degli acquiferi, finalizzata alla valutazione degli scambi idrici sotterranei tra i Monti Lepini e la pianura Pontina

Abstract

This paper tells about the hydrogeological studies carried out to evaluate groundwater exchanges between Lepini Mountains carbonatic ridge and the Pontina Plain, Latium Region (Fig. 1), by means of numerical model simulations. The study area has been investigated several times in the past (Mouton J.,1977; Celico et al.1983), with concern about quantitative hydrogeology regarding both Lepini Mountains and the plain and also the exchanges with nearby hydrogeological bodies (Colli Albani volcanic one and Valle Latina alluvial one). More recent studies (Petitta M., 1994; Celico F., 2002) have developed finite differences numerical models about the carbonatic ridge only, while the conceptual and numerical model presented here is the first that analyze groundwater relations between the ridge and the plain. To do so the work has sorted many pieces of information about the geological setting, focusing specially on the fractured ridge characteristics in order to set the equivalent porous media hypothesis. Moreover, the artificial channel network of the plain has been taken into account, considering its role for land reclamation draining areas otherwise flooded. Great importance has been given to the springs located at the bottom of the ridge, because they are the most significant expression of groundwater circulation. The spring recharge areas have to be determined and bounded in order to plan water management actions. The model calibration has allowed achieving this goal, putting together the ridge partitioning due to tectonics arrangement and the flowpath approach. Calibration results have yielded hydraulic conductivity values that minimize specific target residuals; target points are located both in the ridge and the plain and concern head and flow measurements. The numerical model runs steady state simulations and the implemented boundary conditions have been the constant heads, the No-flow cells, the pumping wells and the drains. Model reliability has been tested through residual analysis, as formerly mentioned. This model can be put down as a regional Screening one (Feinstein et al., 2006), therefore it cannot be used to simulate local groundwater behavior. It can be used to understand and improve circulation pattern knowledge and to test conceptual model hypotheses to identify areas where further analysis is necessary with new hydrogeological information.