Geoelectric monitoring in a lime-alpine gravel body in the period November 2019 to October 2020: A hydrological-oriented case study from the Gesäuse National Park

This case study, using geoelectric monitoring, deals with the measurement of electrical conductivity in a calcareous gravel body. The change in electrical conductivity was observed from November 2019 to October 2020 (nine terrain campaigns) in a gravel pit in the Gesäuse National Park (Johnsbachtal, Styria). The Langgriesgraben in the Reichenstein group is part of a coagulation with high morphodynamic activity that drains into the Johnsbach, which runs transversely to the trench. The Langgriesgraben, which is filled with main and weather stone dolomite, slope breeks and raible layers, has a powerful groundwater body whose size and location is influenced by precipitation events. The change of the groundwater body as well as the rise and decrease of the groundwater level can be derived from the specific electrical resistance. The geoelectric resistance measurement is carried out in this work with the Wenner configuration, in the data analysis with Res2Dinv the Least-Squares and Time-Lapse inversion methods as well as Bedrock Detection were used. With 17 profiles, with four or two meters of electrode spacing, it could be shown that the electrical conductivity in the Langgriesgraben changes significantly during the course of the year due to climatic conditions. The repeat measurements have shown that the electrical conductivity decreases more strongly on the surface of the Langgries trench in summer than in the underlying layers. In frequent precipitation events, the electrical conductivity increases and leads to an increase in water saturation of the looser sediments in the gravel body and to the regulation of the position and thickness of the groundwater body. The comparison of meteorological data of the WegenerNet in the Johnsbach Valley also showed that the electrical conductivity increases significantly in autumn, both on the surface and in the underground.