The Drava River is a transnational river, originating in the south-tyrolean Alps near the border with Austria. The study site of Drava is located in the eastern Alpine region in Slovenia near the second largest city in Slovenia, Maribor. Upstream of Maribor, the valley widens and Drava River reaches the heavily populated urban areas. Below the urban area of Maribor, in the ice age, Drava River has created a large Drava Field alluvial fan into which it has cut the present valley near the foothills of Slovenske Gorice. Pilot study area reach upstream boundary point is just downstream of Melje dam, where Drava River channel divides into two reaches – one, artificial derivation channel, leading to HPP Zlatoličje powerplant (installed flow 530 m3/s) and the other, natural Drava river channel running at the foothills of Slovenske Gorice, with prescribed environmental flow of 10 m3/s in the winter months and 20 m3/s in the warmer season. These two channels meet again just upstream of Ptujsko lake inlet. The area has been regularly flooded in the last 15 years.
Location and map of the pilot area reach (Maribor/Melje dam – Ptujsko lake inlet) and view of the pilot area reach near Malečnik (downstream of Melje dam) (©IzVRS).
The alteration of the Drava River natural channel morphology between the Melje dam and the Ptujsko lake inlet is mainly i) a consequence of dam construction, ii) city of Maribor wastewater treatment plant outlets and iii) intensive croplands development in the riparian areas and along the main tributaries. Hydromorphological restoration works in the pilot area aims to favour riverbed and riparian maintenance and to enhance flood protection. They concern mainly the restoration and the active management of the gravel bars and the selective management of riparian vegetation (mainly in active bars). The majority of restoration works were in Malečnik area, i.e. in the upper part of the study area. Below is the time-lapse of the works done since 2001. An extensive monitoring activity has been planned to obtain crucial data to enhance the existing survey data (external expertise) and executing geological drill holes to obtain lacking riverbed samples for sediment transport modelling.