Environmental monitoring of hydropower plants is lacking in the Danube basin in Southeast Europe

Environmental monitoring of hydropower plants is lacking in the Danube basin in Southeast Europe

My name is Helena Huđek and I study the ecological impacts of hydropower plants in Southeast Europe. My goal is to develop a simple and inexpensive monitoring guideline which could be applied by state authorities and implemented in their regular monitoring programmes. The aim of the monitoring guideline is so the environmental impacts of hydropower plants are noticed on time and that mitigation measures can be implemented as soon as possible. State authorities would then be able to control the management and operation of existing hydropower plants, which currently barely happens, and they could stop illegal management and operation practices of the plant.

My recent study published in Renewable and Sustainable Energy Reviews (can be downloaded here) is focused on the number, geographical distribution, and trends of hydropower plants and the availability of environmental monitoring data (data on hydrology, fish and benthic invertebrates). We analysed whether available environmental monitoring data would allow an assessment of the ecological impacts of hydropower plants on tributary rivers of the Danube in Slovenia, Croatia, Bosnia and Herzegovina, Serbia, and Montenegro.

Currently, 636 HPPs are operating along the tributaries of the Danube in Slovenia, Croatia, Bosnia and Herzegovina, Serbia, and Montenegro. 42 of which were large (>10 MW), 72 medium (1–10 MW) and 522 small (<1 MW). Large hydropower facilities comprise an overwhelming share (94%) of total installed capacity. This capacity is generated by only 6% of the total number of HPPs. Small HPPs represent 82% of the total number, yet only provide 2% of total installed capacity. In Croatia, Bosnia and Herzegovina, Serbia, and Montenegro, construction activity first focused exclusively on large state-owned hydropower plants, while the construction of small ones has only recently been encouraged by the Renewable Energy Directive and the associated financial subsidy schemes. According to a study from 2015 by the International Monetary Fund, Serbia and Bosnia and Herzegovina were among the world’s top ten countries in terms of energy subsidies as percentage of gross domestic product [1].

After 2000, the number of newly constructed small hydropower plants increased sharply, which was followed by a boom in medium-sized hydropower plants. Total environmental impact of small hydropower plants may exceed the impacts of the less numerous large HPPs in the region, as it was already shown from other regions [2,3]. However, the large number of small HPPs with small electricity output raises also the question of whether the financial subsidy schemes provided at the national level for small HPPs in Southeast Europe are efficient for increasing the share of renewable electricity production. Furthermore, Bosnia and Herzegovina and Serbia plan major increases in the current installed capacity with small hydropower plants.

Official monitoring data were often rather difficult to obtain. The best situation was in Slovenia where the data was partly accessible online or was easily available upon request, while in Croatia very little of the required data could be obtained. In non-EU countries, and especially Serbia, data availability and accessibility were generally worse compared to EU countries. In multi-ethnic Bosnia and Herzegovina, the structural complexity of governmental institutions and the lack of coordination and communication among the various agencies and institutions represent major obstacles to environmental information access.




Small hydropower plant at Lesnička reka in Serbia (left) and its unfunctional fish pass (right)

Our analysis of national monitoring programmes showed a broad lack of consistent and comprehensive monitoring data. Hence, only 2.2% of HPPs could be surveyed using hydrological monitoring stations, 0.9% by fish monitoring stations, and 0.6% by benthic invertebrates monitoring stations. None of the hydropower plants have been equipped with suitable adjacent monitoring sites capturing both altered and unaltered states for all three parameters. The number of monitoring stations located near hydropower plants is obviously far below acceptable levels, and the same is true for reference stations outside the affected river section. In addition, there is almost no recent data available from targeted monitoring programmes which assess the ecological impacts by small hydropower plants, and only very little data for larger ones. This data gap also prevents an adequate assessment of the ecological impacts of planned hydropower projects, as well as the identification of appropriate measures to mitigate the environmental effects of existing hydropower plants.




Small hydropower plant at Tripušnica river in Serbia (left) and sediment flushing downstream (right) of its weir which is deadful for most of the aquatic biota

An additional 1315 hydropower plants are currently planned to be built, mostly in Serbia and in Bosnia and Herzegovina. Most planned hydropower plants in the study region are small, though they may still cause significant damage since they extend to almost every river and are unfortunately often constructed on rivers that have high ecological value [4,5]. The fact that 19.4% of all new hydropower projects are planned in protected areas shows that this practice contradicts guidelines for hydropower development in the Danube basin [6], which emphasizes protected sites as “no-go” areas, or that very high thresholds are set in terms of impact mitigation and compensation [7]. It is important to note that the total inland area designated as protected in Bosnia and Herzegovina and Serbia is small; indeed, the percentage of total state territory is significantly below the European average (1.4% in Bosnia and Herzegovina, 7.56% in Serbia) [8,9].



Empty river beds downstream of hydropower plant Davidkovo at River Davidskovska reka (left) and Rosa at River Levi Iskar in Bulgaria (right)

Therefore, a denser and strategically designed network of monitoring stations should be initiated to provide continuous information on biological and hydrological markers. Additionally, the monitoring of water bodies affected by hydropower plants should measure the effectiveness of mitigation measures (e.g. effectiveness of fish passes, occurrence of sediment flushing) proposed in environmental impact assessment, but should also evaluate if the quantities and schedules of environmental flow releases are appropriate. This could be partly done by increasing the number of operational and investigative monitoring stations under the Water Framework Directive, as similarly mentioned by Carvalho et al., 2019 [10].

Helena Hudek focuses on Ecosystem Research and is a doctoral student at the Leibniz- Institute for Freshwater Ecology and Inland Fisheries in Berlin.


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[3] Mayor B, Rodr I, Montero E, Elena L. The role of large and small scale hydropower for energy and water security in the Spanish Duero Basin. Sustainability

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[7] European Commission. Guidance on the requirements for hydropower in relation to Natura. 2000. p. 1–83. 2018.

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[10] Carvalho L, Mackay EB, Cristina A, Baattrup-Pedersen A, Birk S, Blackstock KL, et al. Protecting and restoring Europe ’ s waters: an analysis of the future development needs of the Water Framework Directive. Sci Total Environ 2019; 658:1228–38. https://doi.org/10.1016/j.scitotenv.2018.12.255.