# Detection of Preferential Water Flow by Electrical Resistivity Tomography and Self-Potential Method
## 1 Introduction
These marks are covered by the 6 to 14 m thick, less consolidated, landslide mass extending from the Mosel River to the Upper Muschelkalk cliff (Figure 1c). The landslide mass cover consists of dolomite blocks embedded in a silty matrix. The landslide mass, through which the landslide occurred, was formed during a long-term morphological evolution of the hillslope by alteration and erosion of the Middle Muschelkalk marls and rockfall of dolomite blocks from the Upper Muschelkalk cliff. There is a local fault trending in a SW-NE direction along the southern border of the study area (Figure 1d). It can be assumed that the fault marks the maximal extension of the landslide to the south as more resistant rocks of the Lower Muschelkalk are located at shallow depth southward of the fault.The top of the Lower Muschelkalk (mu) formation is located at 30.7-42.5 m depth below the surface northward of the fault in the study area. The lithological units of Lower and Middle Muschelkalk correspond to the international chronostrigraphic stage of Anisian and Upper Muschelkalk to Ladinian, respectively. The hydrogeological settings of the study area are characterized by fracture flow in a carastic network of the dolomitic Upper Muschelkalk layers. It is supposed that groundwater flows through the spaces in the dolomites, accumulates on the underlying less conductive Middle Muschelkalk, and is drained in the landslide mass where it occasionally reappears as springs. In the study area, several groundwater springs can be observed discharging from the landslide mass deposits (Figure 2a). Additional water supply for the springs is provided by the Kelsbach Creek that flows on the plateau at the rear of the dolomite cliff (Figure 2a). The creek completely disappears in the dolomite massif, and only during periods of intensive rainfall is a surplus of water drained through the creek bed to the Mosel River. Tracer tests carried out in 1968 confirmed the presence of the karstic network in the dolomitic rock massif, resulting in a groundwater flow from Kelsbach Creek to the springs in the landslide's area [44]. Previous studies describe preferential flow in the dolomites of Upper Muschelkalk, whereas the marls of Middle Muschelkalk are supposed to be less conductive material [44]. Therefore, the initial conceptual hydrogeological model of the study site assumed intense groundwater flow discharging from the dolomites and following the way through the landslide mass cover toward the Mosel River. However, the field studies described later below indicated that an intense preferential flow in the marls can occur as well, as it is shown in Figure 2b. Figure 1: (**a**) Regional location of the study area (modified after [41]), (**b**) hillshade map showing location of the study area affected by the landslide in the Mosel River valley, a 3D geological model of the study area (**c**) with and (**d**) without landslide mass cover (processed from [42; 43]). Figure 2: (**a**) Geological sketch of the landslide area showing distribution of boreholes and groundwater springs (**b**) geological section of the area showing conceptual hydrogeological settings (processed from [42,43]).