GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 Waterborne electromagnetcs: two case studies S. Galli 1 , A. Signora 1 , J. Chen 1 , F. Schaars 2 , M. Grohen 3 , G. Fiandaca 1 1 The EEM Team for Hydro and eXploraton, Dep. of Earth Sciences A. Desio, Università degli Studi di Milano, Milano (Italy) 2 Artesia Water, Schoonhoven (The Netherlands) 3 Wiertsema & partners, Tolbert (The Netherlands) Introducton Interactons between surface water and groundwater are the key for a good understanding of the hydrologic system (Harvey and Goosef, 2015). In order to describe the hydrologic system, it’s mandatory to have a good knowledge of hydrogeological setngs below the water column of water. Non-invasive geophysical methods provide spatal informaton on subsurface propertes, but on water bodies has always been difcult (Sheets and Dumouchelle, 2009) or impossible. Electrical and electromagnetc (EM) methods are among the most used geophysical techniques for hydrology (Christansen et al., 2006; Siemon et al., 2009). Among the electrical methods, electrical resistvity tomography (ERT) has been used a lot for aquatc applicatons (Manheim et al., 2004). ERT surveys can be performed in many diferent confguratons: with a towed foatng cable, with stll foatng cables or with cables placed on the botom of the water body. Transient electromagnetc (TEM) and frequency domain EM methods have been used too for hydrology (Ong et al., 2010) and exploraton (Munk et al., 2016). Airborne methods have proved themselves reliable at mapping beneath water bodies (Fiterman and Deszcz-Pan, 1998), but they are expensive and have lower vertcal and lateral resoluton than ground-based methods (Hatch et al., 2010). The tTEM system (Auken et al., 2018), developed in Aarhus University, provided the necessary framework for adaptng it to a foatng EM system. The waterborne version of the tTEM system is referred to as FloaTEM (Maurya et al., 2022). In Lane et al. (2020) the FloaTEM system was used, in tTEM confguraton without modifcatons, on rivers to characterize the hydrological systems. In this abstract, two applicatons of FloaTEM mapping carried out in freshwater lakes are presented, in very diferent geological environments: the southern shore of the Iseo lake in the Brescia province (Italy) and the artfcial Ijsselmeer lake in the Netherlands. Methods and results For the data acquisiton it was used a tTEM system adapted to work on water: the instrument is mounted on a boat made of plastc (to avoid spurious EM coupling in the measurements) that pulls other two smaller plastc boats carrying transmiter loop and receiver loop. To adapt the system for the waterborne survey, plastc supports were built to accommodate the instrumentaton and to avoid cables to touch the propeller. Furthermore, an echo sounder synchronized with a GPS were