| Small hydro
and others indicate the cumulative impacts of small run-of-river dams can be considerable. “We found that many dams being planned in Bulgaria will contribute little to hydropower production but have a disproportionately high impact on fragmentation, while some dams in Greece and Montenegro will have more favourable trade-offs,” the authors state. “In Romania, small HPPs make up 69–86 % of existing hydropower dams but provide only ~3 % of the country’s electricity production. Clearly a critical reappraisal of the benefits of building small hydropower dams is urgently required,” they conclude. The authors go on to add that they believe their
simulations to estimate the loss of connectivity that could occur under different scenarios of planned hydropower plant construction and additional hydropower capacity, while also accounting for dam location in relation to conservation hotspots. They simulated nine dam construction scenarios that varied depending on the number, location, and size of the planned dams. The authors’ analysis estimated that in order to achieve a 25GW increase in hydropower capacity a ~50% loss in river connectivity would occur if small dams were built, compared to a ~20% loss building large dams. Simulations in the Austrian Alps also indicated that building small run-of-river projects would cause more cumulative ecological impacts than building a smaller number of larger dams of the same combined capacity. Likewise, the authors state the construction of many small hydropower plants in Brazil is expected to result in a loss of connectivity five times greater than that caused by the construction of large hydropower dams.
Fragmentation Balkan rivers are currently fragmented by 83,017
barriers and have an average barrier density of 0.33 barriers/km (after correcting for barrier underreporting). This is 2.2 times lower than the mean barrier density found across Europe and serves to highlight the relatively unfragmented nature of these rivers. However, this new analysis shows that all simulated dam construction scenarios would result in a significant loss of connectivity compared to existing conditions. The largest loss of connectivity (-47%), measured as reduction in barrier-free length, would occur if all planned dams were built, 20 % of which would impact on protected areas. The smallest loss of connectivity (−8 %) would result if only large dams (>10 MW) were built. In contrast, building only small dams (<10MW) would cause a 45% loss of connectivity while only contributing 32% to future hydropower capacity. Carolli et al claim that micro-hydro development has widely been promoted as a less impactful alternative to the construction of large dams, but believe their study
results can help decision makers understand the trade-offs between new hydropower developments and fragmentation, particularly the small benefits and high impact of small hydropower stations, as well as helping identify those dams that will have a high impact on fragmentation and a low contribution to energy production. Strategic Environmental Assessments (SEA) in the Balkan rivers do not currently consider the impacts of hydropower and so development “has tended to proceed with little or no strategic planning, or adequate consideration of cumulative impacts at the scale of entire river basins or regions”, the authors go on to claim in their study. “We suggest that any further hydropower development in the Balkans should be subjected to SEA at the basin level in a way that explicitly acknowledges the loss of connectivity and the wider impacts of barriers on river biodiversity,” they add, stressing that hydropower schemes which “generate substantial energy with minor environmental impacts on fragmentation and biodiversity should be prioritised”. “Ultimately,” Carolli et al said, “the aim of our study
was to help decisionmakers better understand the consequences of planned hydropower developments by quantifying trade-offs between gains in hydropower capacity and losses in river continuity.”
References
Mauro Carolli, Carlos Garcia de Leaniz, Joshua Jones, Barbara Belletti, Helena Huđek, Martin Pusch, Pencho Pandakov, Luca Börger, Wouter van de Bund. Impacts of existing and planned hydropower dams on river fragmentation in the Balkan Region. Science of The Total Environment, Volume 871, 2023, 161940. ISSN 0048-9697.
https://doi.org/10.1016/j.scitotenv.2023.161940
Left: Canyon of the Tara river in Montenegro and Bosnia and Herzegovina
Below: Valbona river in Albania
Below: The River Drina forms a large portion of the border between Bosnia and Herzegovina and Serbia
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