| Sedimentation
Left: Baihetan Dam and hydropower station under construction in China. Studies here have looked at the relationship between sediment deposition and hydropower cascades
References
https://www.usgs.gov/ international-programs/news/ usgs-continues-support- ecuador-catastrophic-river- erosion-hazard
https://www.fisheries.noaa. gov/feature-story/klamath- river-reshapes-itself-flushing- flows-move-reservoir- sediment-downriver
More than 50 dams have been built over the
last two decades and to evaluate their impacts and their re-operations on sediment trapping and routing, the authors developed an integrated modelling framework combining models of hydrological processes, dam operation, and sediment connectivity. Their results indicate that the 3S river basin has lost approximately 60% of its annual outlet sediment load due to the cumulative impact of its largest hydropower dams. Moreover, the basin is experiencing an annual loss of approximately 0.32% of its total water storage capacity due to sediment trapping by reservoirs. However, smaller reservoirs are experiencing more pronounced reductions in storage capacity with losses reaching up to 3% per year. Ultimately, reservoir sediment depositions and the subsequent decrease in storage capacities are impacting reservoir water releases and, consequently, hydropower production. Despite being minimal, the interaction between hydrology and sediment dynamics exists, and are likely to accumulate as dams continue to operate over long horizons. After further modelling, their analysis revealed that the operational space of the existing reservoir configuration is limited, and dam reoperation can only marginally enhance the 3S sediment loads. This outlines the importance of integrating reservoir water release strategies with sediment release policies, such as drawdown flushing. By considering such measures, Invernizzi et al say the trade-off between hydropower production and outlet sediment loads would have been more pronounced. Consequently, the re-operation of dams could play a more significant role in mitigating hydroelectric production losses.
Vietnam The Vu Gia Thu Bon (VGTB) river basin in Vietnam is
ranked as the country’s fourth highest in hydropower potential but faces difficulties in maintaining water supply and controlling saltwater intrusion. In turn this is proving to be a challenge for the local population’s domestic and agricultural water supplies. Research by Bonh Quang Nguyen et al in Scientific Reports explains that hydropower development in the region has become a focal point for discussion and has highlighted the complexities of water resource management. Their findings show that dam development, sand mining and changes in land use are the main factors responsible for the decreased flow discharge and sediment morphodynamic alterations, which have led to riverbed incision and saltwater intrusion in recent years. The authors warn that future increased urbanisation in the study area will be accompanied with an increased demand for water supplies, and will be further compounded during times of drought. They say their findings provide a scientific basis for policymakers and decision maker to design and implement an effective and integrated approach to water resource management in the river basins to ensure sustainable future development. “A complex river network connects the VGTB River basin,” the authors conclude. “Therefore, to investigate the basin in detail, especially under the impact of climate change and anthropogenic activities, it is necessary to collect data and establish a full hydro-sediment-morphodynamics model. “From there, we can fully understand the effects of cascade dams, sand mining, and diversion on flow discharge, sediment budget, and morphological change.”
Li, J., Gao, Y., Cao, L. et al. Sediment deposition within cascade reservoirs: a case study of Baihetan Reservoir in the lower Jinshajiang River, China. Sci Rep
13, 20706 (2023). https://doi. org/10.1038/s41598-023- 48052-1
Yinjun Zhou, Guiqiao Wang, Huali Wu, Peng Chen, Dongfeng Li, Zhongwu in, Chao Guo, Shi Ren, Yu Gao. Changes in flow and sediment transport caused by cascade hydropower in the upper reaches of Yangtze River and their influence on spawning of Coreius heterodon. CATENA Volume
235, February 2024, 107622.
https://doi.org/10.1016/j. catena.2023.107622
Invernizzi, B., Tangi, M., Mahto, S., Galelli, S., and Castelletti, A. Reoperating hydropower dams to improve sediment connectivity in the Mekong river basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24- 7614,
https://doi.org/10.5194/ egusphere-egu24-7614
Binh Quang Nguyen, Sameh A. Kantoush, Tetsuya Sumi. Quantifying the consequences of unsustainable sand mining and cascade dams on aspects in a tropical river basin. Scientific Reports 2024. 14:1178. https://
doi.org/10.1038/s41598-024- 51405-z
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