GNGTS 2014 - Atti del 33° Convegno Nazionale

higher than 100%). Therefore, the right bank has constantly a higher resistivity with respect to the background, which may be caused by a constant flux of new glacial water poor in ions. Al already mentioned in a previous chapter, together with the ERT technique we applied also the DTS methodology: Given the double-ended configuration chosen, it is necessary to lead back the temperature profile to the effective length of the borehole perforation and this has been achieved by averaging each “onward” temperature value with the correspondent “backward” value. Hence, each ultimate temperature profile has a length equal to 96 m with 97 temperature values (4 meters at each fiber-optic end have been removed since they are located outside the borehole). The four temperature profiles available so far are displayed and compared in Fig. 3, where also the relative positions of both Vermigliana creeks and riverbanks are indicated. All these profiles show a common trend, which can be detected in each trace and analysed according to the partitioning in Fig. 3: − Part 1: These segments are characterized by the highest temperature values, since here the fiber-optic cable is rather shallow. Therefore, there is a strong influence of the superficial temperature, which is probably also combined with the effect of the waters from the effluent nearby; − Part 2: In this portion, the trend of each T profile is fairly linear and the temperature values are relatively high. Also here, there may be an influence from the effluent of the lakes upstream; Fig. 3 – Comparison between DTS temperature profiles acquired in the Vermigliana site. In each profile five segments can be identified: 1, initial part influenced by the lakes’ effluent and the surface temperature; 2, left bank of the Vermigliana creek (comparable with the left bank of the ERT cross section); 3, Vermigliana creek; 4, right bank of the Vermigliana creek (comparable with the right bank of the ERT cross section); 5, fiber-optic cable rolled at 0.5 m below ground level. All the temperature profiles show the same trend, with higher temperatures in the left bank and lower values in the right one, while the hyporheic zone below the Vermigliana creek is characterized by a variable trend that sharpens over time. GNGTS 2014 S essione 3.2 133