Time Lapse Electrical Resistivity Tomography, Distributed Temperature Measurements and Modeling in the Hyporheic Zone of an Alpine River.

Wednesday, 17 December 2014
Jacopo Boaga1, Laura Busato1, Maria Teresa Perri1, Guglielmo Strapazzon1, Damiano Pasetto2, Mario Putti2, Karina Cano Paoli3, Bruno Majone3, Alberto Bellin3 and Giorgio Cassiani1, (1)University of Padua, Department of Geosciences, Padua, Italy, (2)University of Padua, Department of Mathematics, Padua, Italy, (3)University of Trento, Department of Civil and Environmental Engineering, Trento, Italy
The hyporheic zone is a very complex transition zone, where interrelated hydrological and biogeochemical processes take place, mainly controlled by the exchanges of water between the stream and the surrounding riparian zone and underlying aquifer. Modeling may offer an opportunity to deepen our understanding on how these important ecosystems work. However this is only possible if hydrological and biogeochemical models are coupled to measurements that can constrain the model predictions and lead to robust estimates of the system key parameters and processes. Monitoring of the hyporheic zone faces similar problems of groundwater monitoring, often exacerbated by the strong physical biogeochemical gradients that characterize this transition area. Geophysical time-lapse techniques can provide a dynamic monitoring of the hyporheic and riparian zones.We installed in the hyporheic zone of the Vermigliana creek, Trentino, Italy, a monitoring system composed of (a) an Electrical Resistivity Tomography (ERT) apparatus for time-lapse monitoring of electrical resistivity changes, (b) an optical fiber for DTS monitoring of temperature. The installation below the river bed was done thanks to the recent horizontal directional drilling technology capable to be remote-guided during perforation. We installed 48 electrodes below the stream,plus 24 electrodes on the top of the riparian zone, thus closing nearly entirely the region to be monitored. Parallel to the ERT cable we also installed raman technology fiber optic cable for the distributed monitoring of the subsoil temperature. We present here the results of the time-lapse measurement surveys of the first year, together with the flow/transport modeling conducted to link quantitatively the data collected to the hydraulic parameters of the system. The hyporheic zone evidences an active underflow dynamics that, to be correctly described, needs accurate distributed variably saturated flow and transport modeling.