Hydrogeophysical approach to measure hydraulic parameters on unsaturated rocks

In the past decade, over-exploitation has led to a de- pletion of water resources, with impact both on quality and quantity. A sustainable groundwater management needs a detailed scientific knowledge of the behaviour of the un- saturated zone. Particularly, the evaluation of the flow- rate in the unsaturated zone is important to estimate the travel time of the infiltrated water in the subsurface and, hence, to assess the recharge rate and groundwater vul- nerability. A quarry of calcarenite near the town of Canosa, in South Italy, has been chosen to perform the field tests using an integrated hydrogeophysical approach, combin- ing infiltrometer measurements with electrical resistivity tomography (ERT). The infiltration data were collected using a metallic infiltrometer ring of 0.5 m in diameter, installed directly on the rock, filled with about 8 L of water. The test was conducted for many hours at falling head condition, and the water level within the ring was measured by means of a pressure transductor and a metric rod fixed to the ring. Simultaneously, electrical resistivity measurements were carried out using "time-lapse" technique, in order to monitor the dynamics of infiltration/redistribution of the water in the unsaturated zone. Hydrogeophysical data have been acquired for sev- eral hours to obtain a reliable hydrogeological model of the subsurface investigated. Field-saturated hydraulic conductivity has been de- termined for the calcarenite, and ERT surveys support these results.