Groundwater resources allocation key factors mapping in mountainous catchments trough the integrated approach of GIS analysis and water flows monitoring

Hydrogeological maps of mountainous areas are based on the identification of the aquifers, of their boundaries and on the location of main discharge areas (e.g. springs); they are "static" products, giving a description of what have been recorded by field surveys. The main goal of the presented research, granted by Geologic, Seismic and Soil Service of Emilia Romagna region, is to define a methodology to map the combination of groundwater resources allocation key factors in such a way to define the areas where there is the maximum likehood to locate groundwater discharge phenomena, either by point springs or creeks base flow recharge. To get such a tool, however, it's important to manage geological and hydrogeological data according a GIS based approach and, also, to link morphological and geological spatially discretized data to groundwater and creeks base flow data (hydrological data); moreover the results must be validated against some watersheds where location and hydrology of all existing springs and creeks are well known.The chosen pilot catchment for the research is the upper watershed of the Montone river, in the Northern Appennines chain between Tuscany and Emilia Romagna regions (Northern Italy); the catchment is entirely located in the outcropping area of Marnoso Arenacea formation, a torbiditic sandstones mainly to be considered as an aquitard, from an hydrodinamic point of view, but with locally strongly aquifer type behaviour in relation to geological (arenite/pelite ratio) and structural conditions. The watershed extension is 102,8 km2;(real extension, not horizontally projected, derived from the DTM), with an elevation comprised between 1235 and 305 m a.s.l. (average 793 m a.s.l.); average slope is 26,6°. Higher than 0.5 arenite/pelite ratio lithostratigraphic members of Marnoso Arenacea (potentially more "aquifer-type" lithologies) outcrop on a total of 49.7% of the whole area whereas the remainder has a lower value of the ratio. Since July 2002 Montone river stage is continuously monitored by pneumatic water pressure sensors on two section, respectively in the middle of the upper watershed and at the down closure; since November 2002-March 2003 the discharge of a total of 4 springs is continuously monitored, respectively, by 2 electromagnetic induction flow rate meters and by 2 pressure transducers. A total amount of 198 springs (189 inside the watershed, 9 immediately across the main divide) were identified by an accurate field survey, classified from an hydrogeological point of view and georeferenced; on 37 of them, chosen as more important and most representative, a discontinuous monitoring programme was conducted from summer 2002 up to now. To capture not only the groundwater discharge via point springs but also via creeks base flow, on a total of 20 subcatchments, according which the Montone watershed was subdivided, creek base flow and recession coefficients were measured, during the low flow season, by an induced electromagnetic current meter. Concerning the GIS application, a raster analysis has been performed to put in evidence specific combinations of geologicalmorphological factors considered most relevant to define groundwater discharge. Concerning the base geological features (lithostratigraphic units otucrops, tectonic lineaments, quaternary deposits and strata setting) they were derived (ArcInfo format) from the geological survey of the area performed recently by the Geological, Seismic and Soil service of Emilia-Romagna region (CARG project). From the Digital Terrain Model (10 m spatial resolution) the slope and attitude of the relief has been derived; in parallel, from the strata setting, through the interpolating of point data (by Inverse Distance Weighted method and using tectonic lines as breaklines) two different informative layers were derived, both with 50 m spatial resolution and concerning, respectively, strata dipping direction and strata slope. The so obtained 4 different informative layers were overlaid to achieve, by a spatial primary query, the areal occurrence of the condition of coincidence between slope attitude and strata dipping direction and, further on, this occurrence was split down with a secondary query in two conditions: strata with higher or lower slope value than the slope of the relief. The resulted areas distribution was compared with the actual occurrence of springs, with the distribution of spring discharge and with the distribution of creeks base flow; all these hydrological data were regionalized to be matched with the morphological and geological ones. The hydrological discretization has been based on the subcatchments for the creeks data and on the supposed recharge areas for the springs. The hydrographs obtained from the continuous monitoring programme was useful to define the hydrological conditions of the watershed in relation to rainfall distribution and to study the partition of the runoff component of the watershed. The research still is going on to complete the continuous monitoring in different hydrological conditions to take into account and estimate the interannual variability.