ABSTRACT
There are eight hydropower plants (HPPs) on the Slovenian part of the Drava River. Six HPPs (Dravograd, Vuzenica, Vuhred, Ožbalt, Fala and Mariborski otok) are situated directly in the river course, while the other two HPPs (Zlatoličje and Formin) are located in derivation channels of the river. For this purpose, ten concrete gravity dams were built between 1918 and 1978 with a structural height between 17 and 54 m. Due to the great age of these dams, it is necessary to monitor the condition of the dam structures and their surroundings even more carefully, which enables appropriate action in the case of identified deficiencies. These activities are carried out through regular annual technical observations, which include the monitoring of the deformations of the dams and the filtration of groundwater in the wider area of these structures, as well as regular accurate visual inspections. In order to gain a better insight into the condition of dams, some measurements (mainly hydrostatic and partly hydrodynamic) have already been automated. Recently, drones have also been included in the monitoring of dams, which allow insight into the condition of dam structures and their areas of influence, even in hard-to-reach or inaccessible places. Data obtained through technical observation of dams are also used for numerical analyses of dams, namely for the calibration of numerical models for calculating the static and the dynamic safety of dams. The results of the surveillance of these dams showed that, mainly due to the aging of the dam structures and also due to extraordinary events (i.e. flood and equipment failure), the renovations of the dams were necessary. Due to the aging of the dams, the renovation of the oldest dam on the Drava River in Slovenia (Fala Dam) began as early as 1987, which was followed by the renovation of seven more dams (Dravograd, Vuzenica, Vuhred, Ožbalt, Mariborski otok, Melje and Zlatoličje) in the following years. The remaining two dams (Markovci and Formin) still need to be renovated; the renovation of the Markovci Dam is currently underway (it should be completed in 2026), while the start of renovation of the youngest dam on the Drava River in Slovenia (Formin Dam) is scheduled for 2024. The renovation included the revitalization of the mechanical, electrical and structural parts of the dams. After the complete renovations of the dams, the surveillance systems of the dams were updated. Two dams were also renovated due to extraordinary events. The rehabilitation of the Formin Dam - due to damage after floods - was performed between 2013 and 2014, while the rehabilitation of the Mariborski otok Dam - due to damage following equipment failure - was carried out between 2018 and 2020. These dams needed to be properly renovated so that they continue to serve their purpose well in the coming decades.
