Monitoraggio delle acque di fondo del Bus de la Genziana (Pian Cansiglio, Nord-Est Italia)

In this paper we present the results of groundwater monitoring of the Bus de la Genziana (Cansiglio, North-Eastern Italy). It is a cave 587 m deep and about 7 km long with a siphon hanging in the bottom. For the fi rst time a diver instrument was installed here from March 2013 to December 2014 to discover the underground hydrodynamics. The level has been raised with a pattern of impulsive average of 4-5 meters with a few millimeters of rain: it has reached 27 meters in one event and twice it has exceeded 50 meters with heavy rainfall lasting for several days. A direct relationship is between tiltmeters recording (installed here at 25 m deep) and water level in the siphon. Observing the conductivity and the temperature, before the events of fl ood, the conductivity values (EC, at 25°C) were an average of 215 and 260 μS/cm, while the parameter fell between 150 μS/cm and 190 μS/cm when the karstic system fi lls. On the contrary the temperature changes a little bit: the variations are sometimes near the error measurement of the instrument with 0.04 to 0.3° C, minimum values 7.48° C and maximum value 8.34° C. These parameters show that the place can be affected by mixing of new infi ltration water, which is however very fast as a trigger, as less outfl ow. This type of dynamic helps us to understand that the underground water circuits are highly conductive, as confi rmed by tiltmeters signal, and enrich the knowledge of the Cansiglio complex hydrogeology. Prospects for the future are to continue monitoring by installing a diver instrument also in the Abisso del Col della Rizza, a cave near Genziana, 800 m deep, in order to understand better the underground hydrodynamics, which are much more complex than they look.