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Drought climate change hot spots, Su Gologone, Sardinia, water pumping management., Flowpath 2017, National meeting on hydrogeology 2017

Veneto, Friuli-Venezia Giulia, karst aquifer, water budget., Flowpath 2017, National meeting on hydrogeology 2017

Nell’ambito del progetto LIFE+ 08NAT/IT/000369 “GYPSUM” è stato eseguito un monitoraggio idrogeologico tramite acquisitori automatici “STS Datalogger DL/N 70” di sette sorgenti carsiche nei gessi emilianoromagnoli. Le variazioni di conducibilità (mS/cm), temperatura (°C) e livelli idrici (mH2O) misurati nelle sorgenti forniscono utili informazioni sul comportamento idrogeologico dei sistemi carsici studiati. Due delle sorgenti sono sviluppate nei gessi triassici (le risorgenti dell’Acqua Bianca vicino al Passo del Cerreto e quella del rio Vei nell’Alta Val di Secchia), mentre le altre interessano i gessi macro-cristallini messiniani (risorgente del Rio Groppo, in provincia di Reggio Emilia, e le risorgenti del Rio Gambellaro, del SEMPAL, del Rio Basino, oltre che il sifone laterale all’interno di quest’ultima, tutte nella Vena del Gesso Romagnola). Le variazioni dei parametri monitorati, messe in relazione a parametri ambientali di precipitazioni e temperatura dell’aria, hanno consentito di riconoscere diversi tipi di risposta idrochimica ed idrodinamica. Tutti i sistemi esaminati sembrano rientrare nella tipologia di “rete di drenaggio a dreno dominante”, caratterizzata da una rapida variazione dei parametri idrogeologici in funzione delle precipitazioni con aumento dei livelli idrici e diminuzione della conducibilità (tipico fenomeno della sostituzione prevalente). Una di esse, la risorgente dell’Acqua Bianca, mostra chiaramente una ricarica secondaria attraverso travasi da parte dei depositi glaciali, che controllano in parte i processi infiltrativi, con leggeri fenomeni di pistonaggio. Nel sistema di Rio Vei, è ben visibile anche una risposta giornaliera in seguito ai cicli diurni di fusione delle nevi.

Many quarries for the extraction of gypsum are located in the hills of the Monferrato area (central eastern Piedmont). Close to the village of Moncalvo, Asti Province, a subterranean quarry of more than 20 km long is present. During the excavations a fracture from which water gushed at a pressure of 3 atm has been intercepted in 2005. The underground works have been suspended immediately and, after only a few hours a water flow comprised between 3000 and 4000 L s-1 has flooded the quarry tunnels filling a volume of over 60,000 m3. After more than one month of pumping the flooded areas have been made accessible again, revealing a thin rock diaphragm that separated the quarry tunnel from a natural cave, which failed under the high hydraulic pressure. Through this small gap it has been possible to access an extensive karst network that previously was completely submerged. During the following quarry operations a second natural cave has been encountered, belonging to the same system but physically divided from the first cave by some metres of physical sediments. The total development of this cave system is around 1 km. The exploration of these caves has allowed to gather an interesting set of observations that have contributed to elaborating a speleogenetic model. The first information regards the impressive amount of snottites present along the walls of the caves, and the overall thickness of gypsum rock subdued to weathering, reaching up to 30 cm. There are many morphologies that clearly demonstrate the caves being formed in phreatic conditions, such as pendants and corrosion cupola, but also flat corrosion bevels and V-shaped cross-sections, further evidences of formation in saturate conditions. The stratigraphic asset of the area surely has played a fundamental role in the formation of these karst systems. From bottom to top there is a thick shale sequence, and a thin discontinuous and extremely well karstified marly limestone bed that seemed to have enhanced the hydrological flow in the above lying gypsum beds. The principal cave systems are formed in between the first and second bed of gypsum, along a shaly finely stratified interbed rich in organic material. On the floor of the main passage there are many rather small subvertical conduits that develop up to the underlying limestone bed thus favoring the upward movement of water and the dissolution of the gypsum rocks. The subterranean excavations also have intercepted other caves, most of them of much smaller size, often reaching some cubic metres in size and partially filled with large gypsum crystals, grown by the continuous but slow feeding of slightly supersaturated waters.