L'acquifero superficiale del territorio di Brindisi: dati geoidrologici diretti e immagini radar da satellite

Abstract

A free shallow aquifer is present in the Pleistocene marine terrace deposits that widely outcrops in the Brindisi district. These deposits overlay impermeable clay and calcarenite of 'Fossa bradanica' sedimentary cycle, and Mesozoic carbonate rocks of 'Calcare di Altamura' formation. In the latter a regional karsic aquifer is present. The geological analysis was carried out also using stratigraphic data from drilled holes. Those data highlight a local high variability of aquifer and impermeable clay thickness, with a mean value of 14 m and 22 m respectively. On line with the results of hydrologic accounting, particular attention was paid to the recognition of local water loss toward the karsic aquifer. A hydrogeologic study of a sample area southward with respect to Brindisi, based on detailed field survey, highlights low values of aquifer permeability, with mean value of 7,5 x 10-5 m/s. The permeability of the clay deposits underlying the aquifer is too high to avoid any water infiltration (mean value of 3 x 10-7 m/s). The water table is locally influenced by hydrographic pattern. If we consider piezometric regimen it has a month minimum in the summer end and a month maximum in March or April, with a delay of 2-3 months with respect to month extreme rainfall. The analysis of a multitemporal satellite radar image provided useful information about the water content changes of the shallow aquifer. The color hue differences shown in the color composite image of three images acquired in different season, are strictly correlated to the changes in soil moisture content. Besides, structural lineaments were recognized in that image, along which water infiltration is likely. The applicability of remotely sensed data in this kind of study is also proved by the analysis of images acquired by an infra-red videocamera.