GNGTS 2014 - Atti del 33° Convegno Nazionale

− Part 3: These segments correspond to the sub-riverbed of the Vermigliana creek. Here the trend is more variable than the other parts and sharpens over time, given the complexity of the processes taking place (e.g., mixing between glacial water and rain water with ground water); − Part 4: This part of the traces is relative to the right bank and is clearly characterized by the lowest temperature values, probably due to the flux of glacial water; − Part 5: This portion represents the part of the fiber-optic cable in excess that has been rolled and located at a depth of 0.5 m below ground level. A time-lapse analysis of the profiles in Fig. 3 highlights a temperature increase over time: In fact, from the first to the last survey, the mean temperature augments of 2.09 °C. This temperature variation is not constant along the whole fiber, since the left bank warms up a little bit more than the right bank (i.e, mean increase for the left bank = 2.67 °C vs. mean increase for the right bank = 2.12 °C): this is also confirmed by the T variation computed for each sampling point. Therefore, not only we can assume that such temperature variation over time is instrument independent, but also we can hypothesize that the left and right riverbanks behave in two different ways, or, more likely, that are subject to different phenomena (i.e., flux of lacustrine and glacial water, respectively). Finally, what needs to be strongly highlighted is the relation existing between DTS and ERT data, well proven by the comparison of Fig. 3 with the results of the time-lapse inversion. The relatively higher temperature values characterizing the left bank of the Vermigliana creek well fit the decrease in resistivity described before, since both this two effects may be caused by a sub-superficial flow of lacustrine water, which is hotter and richer in ions with respect to glacial water. On the contrary, a sub-superficial flux of glacial water may explain the overall lower temperature of the right bank and its relatively higher resistivity, given the lower ions contents. Future work. The data acquired so far need to be coupled with a flow and transport model, in order to completely describe the structures and the processes characterizing the HZ of the Vermigliana creek. To achieve this future goal, we will use the CATHY(CATchment HYdrology) model combined with data assimilation methods, thanks to whom it is possible to assimilate both ERT and DTS data inside the numerical model itself. Furthermore, the time-lapse monitoring of the hyporheic zone of the Vermigliana creek will continue in the next years, given the need of analysing more in detail the applicability of these two non-invasive methodologies in such a unique domain. Conclusions. One of the main problems in the HZ characterization is the obvious need of investigating a domain located under a riverbed. In order to overcome such a problem, we applied two non-invasive methodologies, ERT and DTS, with an innovative instrumentation deployment: Both a multicore cable and a fiber-optic cable are located into two horizontal perforations drilled below the Vermigliana creek. Thus, the instruments are inside the HZ, our domain of interest. These two methodologies not only allowed fast surveys, but also supplied several high-quality datasets, comprising both resistivity values and temperature profiles that permitted a time-lapse analysis of the investigated area. The comparison between these different data highlighted a complex domain, characterized by the interaction of waters with different origin (e.g., glacial, superficial, and groundwater). Therefore a combined application of ERT and DTS measurements can lead to a deeper characterization of the hyporheic zone, given the strong correlation existing between the physical parameters analysed. Hence, the preliminary results presented in this work already show their high potential, which, however, will be fully expressed only through an appropriate hydrological modelling. 134 GNGTS 2014 S essione 3.2