Dam safety | of the problem of ageing dams”. ICOLD said
it reiterates its wish to work on dam safety with all concerned institutions and believes that this very important subject deserves better communication.
Australian action WaterNSW has announced that investigations are
underway to address safety concerns and ensure the long-term security of Warragamba Dam in Australia. The dam, one of the largest domestic water supply dams in the world which supplies more than 80% of Sydney’s water, currently remains safe for day-to-day operations and is structurally sound, but is being examined in light of the potential risks posed by extreme floods and the impact of climate change on downstream communities. WaterNSW regularly conducts risk assessments of its dams and implements upgrades as necessary to meet contemporary dam safety regulations, it said. A recent risk assessment of Warragamba Dam has identified potential climatic and geotechnical risks
under extremely rare weather conditions. Although there are no immediate structural concerns regarding the dam wall, additional measures may be required to mitigate the effects of extreme floods associated with climate change, considering the large population downstream. WaterNSW emphasised that Warragamba Dam is capable of withstanding even the most severe floods. However, in accordance with evolving safety standards and in anticipation of climate- related challenges, the organisation is committed to ensuring the dam’s compliance with the latest NSW dams’ safety regulations. The specific actions, whether they involve infrastructure modifications or non-infrastructure solutions, required to address the identified risks are yet to be confirmed. Investigations are now underway to evaluate the necessary measures and guarantee the dam’s ongoing compliance with safety regulations. Earlier in the year WaterNSW successfully restored function to critical inlet infrastructure at Lake Brewster
Safety in papers
Tailings Dams According to a new paper by Ouellet et al, recent tailings dam failures highlight important gaps in current monitoring methods. Here the authors demonstrate how ambient noise interferometry can be applied to monitor dam performance at an active tailings dam using a geophone array. They implemented a power-law relationship between effective stress and shear wave velocity, and the resulting one-dimensional model shows good agreement with the seismic velocity changes. The authors conclude that as shear wave velocity provides
a direct measure of soil stiffness and can be used to infer numerous other geotechnical design parameters, this method provides important advances in understanding changes in dam performance over time.
Plastic threats According to Gao et al, hydropower dams can impact the transport of microplastics from rivers to the ocean. The authors say that enrichment of microplastics in reservoir surface water close to dams confirms a pressing need to determine the impact of dam construction on the mass-imbalance between plastic debris entering the ocean, and that observed in the ocean. The authors claim that dams are known to exacerbate the accumulation of organic pollutants, heavy metals, nitrogen, and phosphorus but their effect on sedimentary microplastics is largely unknown and to date, research on microplastic contamination in reservoirs is sparse. Gao et al set about looking at the Yangtze River, which is the
world’s third-largest river and the largest input of oceanic microplastics worldwide, and report microplastic concentrations and compositions across a range of size fractions for sediment samples collected in the upper and lower reaches of the Three Gorges Dam in 2008, 2015, 2019 and 2020. They found a gradual increase in microplastic abundance over time, with preferential retention of small-sized microplastics in the dam reservoir sediments, and estimated that the total plastic mass load in reservoir sediments indicates the Three Gorges Dam retains as much as 47±44% of the Yangtze River microplastic flux to the ocean. As such, the growing microplastic stocks in reservoir sediments suggest that dams may selectively trap large amounts of small-sized microplastics.
Above: Research into microplastics at the Three Gorges Dam in China has concluded that a remarkable amount of terrestrial microplastics is not exported to the ocean due to dam entrapment
“Our results demonstrate that a remarkable amount of
terrestrial microplastics is not exported to the ocean due to dam entrapment, underscoring the importance of accounting for dams when investigating global riverine microplastic transport. Thus, the focus should be placed on the microplastic burdens of global-scale reservoirs,” the authors conclude. “Moreover, dam construction alleviates the oceanic burden of microplastics and provide a potential opportunity for future oceanic plastic remediation. Also, the transformation of reservoir dispatching methods could enhance the possibility of regulating the flux of microplastics to the sea.
References
Ouellet, S.M., Dettmer, J., Olivier, G. et al. Advanced monitoring of tailings dam performance using seismic noise and stress models. Commun Earth Environ 3, 301 (2022).
https://doi.org/10.1038/s43247-022-00629-w
Gao, B., Chen, Y., Xu, D. et al. Substantial burial of terrestrial microplastics in the Three Gorges Reservoir, China. Commun Earth Environ 4, 32 (2023).
https://doi.org/10.1038/s43247-023-00701-z
24 | August 2023 |
www.waterpowermagazine.com
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