Hydro-ecologically based operation of run-of-river reservoirs for effective sediment management and energy production

Here we present the main activities of an ongoing project aiming at effective sediment management in run-of-river reservoirs. Climate change is reflected mainly in a gradual increase of temperatures, which result in longer dry periods, frequently followed by heavy rainfalls, causing increased intensity and occurrence of floods and erosion processes. The changed hydrological conditions require proper adjustments of water management practices. Construction of water reservoirs, used for hydropower generation, offers the possibility to adapt to changed hydrological conditions, especially in terms of multipurpose water use. However, hydropower plant reservoirs disrupt the dynamics of sediment transport and may have a negative impact on the riverine environment and water organisms.  Sediment management under changing hydrological conditions is a challenge of global proportions, existing sediment management practices in water reservoirs worldwide are mostly unsustainable and lead to the loss of the multifunctional role of such facilities, such as loss of water availability for different uses and reduction of the riparian space, which worsen habitat conditions and self-cleaning capacity of the water body. Advanced, holistic sediment management strategy, which includes all elements of the natural sedimentation cycle and environmental concerns related to potential sediment pollution offers sustainable management solutions. In the presented project, a novel, active river sediment management strategy in hydropower reservoirs of the HPPs on the lower Sava, where 5 dams were built in a cascading system between 1993 and 2017, under changing hydrological conditions, will be developed. The strategy will assure to the highest possible extent of the restoration of natural dynamics of sediment transport, also considering the environmental status of sediments. To establish the presented management strategy, a holistic, interdisciplinary approach, which includes a detailed analysis of hydraulic conditions in the reservoirs and associated sedimentation processes, as well as analysis of pollutants trapped in the deposited sediment layers, will be applied. Based on the gathered data, it will be possible to further define potential measures related to the removal of sediments and the alternatives of their disposal or re-use. The developed sediment management plan for the chain of HPP on the lower Sava River will contribute to the restoration of sediment connectivity along the river course and the improvement of the river channel's ecological role. The authors acknowledge that the research is financially supported by the Slovenian Research and Innovation Agency, research core funding No. P2-0180, and research projects No. L7-50097 and by the HESS d. o. o. Hidroelektrarne na Spodnji Savi.