Groundwater and landslide displacement records of the Eggerberg slope (Gradenbach landslide, Carinthia, Austria)

Groundwater and landslide displacement records of the Eggerberg slope (Gradenbach landslide, Carinthia, Austria) Austrian Research Centre for Forests (BFW)Institute for Natural Hazards, Unit of Torrent Process & HydrologyK. Hagen, T. Zieher, U. Stary‚ E. Lang, S. Riedl, G. Priesch, J. Pichler, J. RojacherFirst published June 2026Contact: [e-mail] OverviewThis dataset documents long-term hydrogeological and displacement monitoring at the deep-seated rock slide Eggerberg, situated in the Gradenbach catchment (Carinthia, Austria). The active mass movement covers approximately 2 km² and reaches depths exceeding 130 m. Owing to its interaction with the Gradenbach torrent system, the instability represents a significant natural hazard for nearby settlements in the Möll Valley. The dataset includes groundwater level and temperature measurements, as well as landslide displacement records collected by the Austrian Research Centre for Forests (BFW). It represents one of the longest continuous hydrogeological and geotechnical monitoring programs of a deep-seated gravitational slope deformation in the European Alps. It extends the existing dataset published in Hormes et al. (2026) by data of several boreholes, not used in the publication. Available groundwater temperature records were compiled and added in the borehole records. Furthermore, the displacement record of the extensometer was reset to zero after the data gap from 1995 to 1999. Dataset DescriptionGroundwater monitoringGroundwater levels were monitored in 15 boreholes including several paired installations designed to observe groundwater conditions in different depth horizons and aquifer systems. Monitoring of the goundwater levels started in 1979, using manual cable light-plummet measurements with an accuracy of approximately 1 cm, and ended in 2024. In the beginning, measurements were generally performed every two weeks, since 1998 usually weekly. Groundwater temperature was measured between 1998 and 2015 with a sensor accuracy of 0.1°C. Continuous digital monitoring of groundwater level and temperature is additionally available for selected boreholes from July 2007 to December 2024 using OTT Orpheus Mini pressure probes. The observation series reveal the presence of approximately four hydrogeologically distinct aquifers within the moving rock mass. Landslide displacement monitoringLandslide displacement was monitored using a wire extensometer installed across the Gradenbach ravine. The instrument measured changes in the distance between the moving landslide mass and the comparatively stable opposite valley flank. The observation record extends from May 1979 to April 2024 and includes the same principal data gap between 1996 and 1998.Initially, measurements were recorded using analogue strip-chart systems and later digitized. In 2006, the monitoring station was upgraded with a continuous digital acquisition system (Thalimedes). To reduce short-term thermal effects caused by steel-wire expansion and contraction, the published dataset contains daily aggregated displacement values. All records (groundwater level and temperature, landslide displacement) were generally quality-controlled and checked for outliers and plausibility before publication. However, no warranty is given regarding their accuracy, completeness, or fitness for any particular purpose. Data StructureGroundwater FilesEach borehole is provided as an individual CSV file (GRD-GWL-[borehole number]):• Column 1: Date (YYYY-MM-DD)• Column 2: Groundwater temperature (°C)• Column 3: Groundwater level below ground surface (m)Missing or unreliable values are coded as 9999. Groundwater levels are reported as negative values relative to the ground surface. Extensometer FileThe landslide displacement dataset is provided as a single CSV file (GRD_EXT.csv):• Column 1: Date (YYYY-MM-DD)• Column 2: Landslide displacement (cm), expressed as reduction of the distance between canyon slopes• Column 3: Measurement and data-quality codeThe PDF document ‘GRD_Zenodo-V1-20260701.pdf’ provides site information, methods, data gaps, and corrected observations. The ancillary document ‘monitoring_data_gradenbach.html’ provides minimal code snippets for working with the data in R. It further includes interactive plots of the data for visual inspection. Scientific RelevanceThe Gradenbach–Eggerberg dataset provides a unique long-term record enables the investigations of groundwater-controlled slope acceleration processes, and temporal trends in aquifer behavior. The dataset therefore constitutes an important resource for landslide process research, hazard assessment, hydrogeological investigations, and model validation.