# Detection of Preferential Water Flow by Electrical Resistivity Tomography and Self-Potential Method
## 5 Conclusions  
Hydrogeological investigation methods in combination with geophysical prospecting were used for the investigation of the hydrogeological settings of a landslide-prone slope in the Upper Mosel valley.  
Observations in piezometer wells show that in the Deisermillen study site, two groundwater flow systems are present: the first being groundwater flow above the less permeable marks and the second located within the marl sediments where preferential flow occurs. Hydrogeological observations in piezometer wells and hydrogeological testing revealed an intense preferential flow in the less conductive marks, which was not expected to occur there. Nevertheless, observations in boreholes are 2D measurements which are not suitable for the complete exploration of heterogeneous groundwater flow conditions.  
A geophysical investigation was also conducted for the investigation of the spatial extension of flowpaths in the subsurface. By applying ERT and self-potential mapping techniques, preferential flow could have been identified in a zone of the hillslope where groundwater from the castle network enters the landslide mass cover and flows toward the Mosel River. However, it is not entirely clear which preferential flow system is the source of the measured self-potential anomalies because the signals are widely spread over a large area. As the interpretation of the geophysical measurements was not straightforward, assumptions based on the geological data were necessary for the conceptualization of the preferential flowpaths in the numerical model.  
The hydrogeological model allowed for the validation of the assumed morphology of a thin, laterally extending preferential flowpath through field observations in piezometer wells.  
The results of this study show that the identification and parametrization of the preferential flow using conventional techniques such as hydrogeological testing and monitoring can be ambiguous. Other data sources, such as knowledge about the local geological settings and numerical modeling could be necessary for better conceptualization and parametrization of preferential flow in the subsurface.  
Integrated application of models, for instance geophysical techniques used for the validation of the hydrogeological simulations, can help to explore the preferential flow. Applying inverted streaming potential signals that the permeability and seepage velocity of the preferential flowpaths can be derived [33]. In the study area of Deisermillen, modeling of the streaming potential signals can be used for validation of the hydrogeological model during the subsequent research.  
Conceptualization, K.K. and J.-F.W.; methodology, K.K.; software, K.K.; validation, K.K. and J.-F.W.; formal analysis, K.K. and J.-F.W.; investigation, K.K.; resources, J.-F.W.; data curation, K.K. and J.-F.W.; writing--original draft preparation, K.K.; writing--review and editing, J.-F.W.; visualization, K.K.; supervision, J.-F.W.; project administration, K.K.; funding acquisition, J.-F.W. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.