Effective infiltration variability in the Umbria-Marche carbonate aquifers of central Italy

Abstract

The spatial variability of the effective infiltration parameter within the recharge areas of the main aquifer complexes of the hydrogeological group of the Umbria-Marche ridge of Central Italy was assessed. This parameter usually varies with respect to lithology and the extent of precipitation in the investigated area. The average effective infiltration, expressed in millimeters/year, was directly computed by dividing the volume of water discharged on average from a hydrogeological basin by the extent of its recharge area. This method does not directly depend on the extent of precipitation, and therefore it is not biased by uncertainty in that value. Effective infiltration was assessed for 15 hydrogeological units and ranges from 200 mm/year to 475 mm/year. The effective infiltration values for the “Scaglia” complex are always lower than those of the other aquifer complexes. The effective infiltration of the “Scaglia” complex increases southwards. This latitudinal spatial variation of effective infiltration is nearly independent of the precipitation distribution. Because this trend is much more pronounced in the “Scaglia” complex, it has been inferred that the spatial variability of the “Scaglia” fracturing is more significant than fracturing in any of the other calcareous lithotypes. The recharge area of the “Scaglia” complex is higher in the northern hydrostructures than in the southern structures because the two areas have different deformation styles. When added to the spatial fracture variability in the “Scaglia”, the effects of this differentiation in deformation are responsible for the different water resource amount of the hydrostructures. The occurrence of wide outcrops of the “Scaglia” complex with reduced infiltration capability justifies the existence of less productive aquifers in the northern hydrostructures.