| Planning & projects
storage capacity and year of construction are known: 28,045 in Asia-Pacific, 2,349 in Africa, 6,651 in Europe, and 10,358 in North, Central and South America. The UNU-INWEH study notes that figures may err on the conservative side. For example, other researchers have estimated the loss from 190 California reservoirs at more than 50% from their original capacities, with 120 reservoirs having lost over 75%. A similar study predicted Japan’s Sakuma reservoir will lose around 44% of its initial capacity by 2040. The authors conclude that the overall magnitude
of water storage losses due to sedimentation is quite disturbing, and that new dams under construction or planned will not offset storage losses to sedimentation. They authors add that their study is sounding an alarm on “a creeping global water challenge with potentially significant development implications”. It only adds to the list of water development issues that the world is already facing and has been unable to resolve.
Methane emissions A new study has detailed how there are ways to
reduce methane emissions from existing and new hydropower plants. Estimated emissions from 9000 reservoirs on five continents has shown that methane emissions will continue to increase in the future, due to the construction of new reservoirs in warmer climates and the resulting degassing or bubbling emissions. The good news is that the design and operation of dams can be changed to mitigate a part of this. One- third of methane emissions from reservoir are the result of degassing – when water that feeds hydroelectric turbines is drawn from deep layers of the reservoir with higher concentrations of methane. Once the water passes through the turbines and released downstream the methane is released into the atmosphere. By drawing water closer to the surface it is possible
to significantly or totally remove emissions from methane degassing. In an example of a Malaysian reservoir, if the intake was located a few metres higher, it was estimated that the amount of methane released could be reduced by about 90%.
Another measure to mitigate emissions could be made by improved management of water levels to limit the presence of shallower areas, which contribute significantly to methane bubbling emissions. The study by the University of Quebec in Montreal said that methane emissions from reservoirs accounted for 5.2% of anthropogenic methane emissions in 2020, but occurred at a small fraction of dams globally.
Platypus The platypus is currently listed as a near threatened
or endangered species in certain parts of Australia. Although the species spends most of its time in the water, it can move over land and has prompted concern that dams may have become barriers to such movement.
As many as 77% of Australia’s major dams that are over 10m high coincide within the regions where platypuses occur. To help ascertain whether this is limiting the species’ gene flow and dispersal that is essential to evolution and ecology, a new study has been published in Communications Biology. The authors examined disruptions of the gene flow between platypus groups below and above five major dams, matched to four adjacent rivers without major dams. Below major dams, altered natural flow regimes, including changing of the timing of flows and important reduction in flow volumes, have been found to significantly impact platypus abundances and demographics. Conditions below and above major dams represent poor foraging and burrowing habitat for platypuses, given lower productivity of macroinvertebrate prey species. Mijangos et al say that their study provides evidence of gene flow restriction, which jeopardises the long- term viability of platypus populations when groups are fragmented by major dams. They recommend that mitigation strategies, such as building of by-pass structures and translocation between upstream and downstream of the dam, should be considered in conservation and management planning. ●
Above: The fragmentation of Australian rivers by major dams can have implications for the future of platypus populations
References
Perera, D.; Williams, S.; Smakhtin, V. Present and Future Losses of Storage in Large Reservoirs Due to Sedimentation: A Country-Wise Global Assessment. Sustainability 2023, 15, 219. https://doi. org/10.3390/su15010219
New study sheds light on reservoir emissions over a long
time period (
hydropower.org)
Mijangos, J.L., Bino, G., Hawke,
T.et al. Fragmentation by major dams and implications for the future viability of platypus populations. Commun Biol 5, 1127 (2022).
https://doi.org/10.1038/ s42003-022-04038-9.
Left: Sediments on the Cunovo Dam on the Danube river in Slovakia. A new report has analysed reservoir storage loss worldwide
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