This year, the LIFE IP RESTART project partner Institute for Hydraulic Research (Hidroinštitut) conducted a hydraulic modelling study to analyse the sediment transport and deposition dynamics for the existing and projected state of the HPP Formin reservoir, using a hybrid hydraulic model. The aim of the study was to test and assess the effectiveness of temporary and permanent sediment depots in Lake Ptuj under various high water level scenarios.
Sediment accumulation in the hydro power reservoirs and high water retention basins is a major challenge in Slovenia and worldwide. Sediment deposition in river accumulations reduces the functional volume needed for power generation and irrigation, and increases the risk of flooding. This sediment build-up not only limits the capacity of electricity generation but also degrades the chemical quality of the water, and compromises the ecological potential of retention basins and accumulations. In the face of climate change, it is crucial to ensure sufficient reservoir volume for flood mitigation and to maintain high quality water for irrigation. Before removing sediments from the reservoirs and sediment traps, it was necessary to study the impact of sediment transport and removal on the morphological status of Lake Ptuj, flood safety and the established habitats. The increasing accumulation of sediments in Lake Ptuj poses a threat to the flood safety of Ptuj and other settlements along the Drava River and Lake Ptuj. It is therefore both necessary and economical to address this issue, particularly from the perspective of flood waves, using modern research methods, including hybrid hydraulic modelling. As part of the LIFE IP RESTART project, this pilot action will establish several areas on Lake Ptuj for the removal of sediments suitable for further use, without adversely affecting the operation of the lake under normal and high water level conditions. This action is also linked to another action within the LIFE IP RESTART project, led by the company Dravske elektrarne Maribor,which focuses on the recycling of dredged sediments to improve flood safety. The action seeks to establish a circular system for the permanent removal, recovery and reuse of sediments to improve the natural dynamics of Lake Ptuj and prevent flooding.
As part of the research, various activities were carried out concerning the sediments of Lake Ptuj and the water flow through the lake. These sediment-related activities included sampling and laboratory analysis of the physical properties of the sediments, as well as hydraulic analysis of their mobility and erosion resistance. Water flow simulations were used to assess the flood safety status of Lake Ptuj, both in its current state and with the proposed sediment management measures. The simulations also evaluated the impact of the planned measures on the passage of the Drava River high water waves through Lake Ptuj and their effects on various defined habitats within the lake.
Visual: Shallows in the central part of Lake Ptuj during low water levels in September 2022
(Source: Institute for Hydraulic Research Ljubljana)
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