A MATLAB GUI program for reservoir management to simultaneously optimise sediment release and power generation

Sedimentation affects the normal function of reservoirs and is a decisive factor in the reservoir's service life. Flushing sediment during reservoir operation is an effective non-engineering measure to alleviate reservoir sedimentation; however, lowering water level to discharge more flow conflicts with hydropower generation. In this study, reservoir management software is developed to simultaneously optimise sediment discharge and hydropower generation with the reservoir discharge as the decision variables. The sediment transport rate is calculated by an integral of the vertical distribution of suspended load concentration and flow velocity instead of empirical formulas. The model is solved by the most widely used multi-objective optimisation algorithm NSGA-II, resulting in the optimal schedule corresponding to the maximal sediment discharge and hydropower generation, which can be displayed graphically in the software. The software was developed in MATLAB with a Graphical User Interface (GUI) and applied to a large reservoir and can be generalised to other reservoirs. The results show that within the recommended discharge variation of 5%, the sediment release can be increased by 2.07 × 10⁶ t as a reduction of per 10¹⁰ kW h in annual power generation. Compared with the original scheme, sediment release can be increased most by 3.31% at the cost of 0.03% loss of power generation. Moreover, the dual objective in the flood season was optimised by 7.30% and 3.92%, respectively.

Dam construction attenuates trace metal contamination in water through increased sedimentation in the Three Gorges Reservoir

Dam construction has a far-reaching impact on trace metal accumulation and the metal-induced quality of the aquatic environment. However, the long-term impacts of dam construction and impoundments on the spatial distribution of trace metals and water quality remain poorly understood. Here, we found that the concentrations of trace metals in the mainstream water of the world's largest reservoir, Three Gorges Reservoir (TGR), decreased after impoundment, while their concentrations and contamination in the sediments of the water-level fluctuation zone increased significantly, especially for anthropogenic sources of metals such as cadmium, lead, and zinc. The spatial and temporal variations of anthropogenic metals in the sediments revealed increased anthropogenic dominance in their distribution under current hydrological management, especially for the urban area of the upper TGR. Sediment fluxes, particle composition, and extreme climate modulated the distribution of trace metals in the sediments. The results demonstrate that human activities have increasingly determined the distribution and contamination state of trace metals in the mainstream TGR. However, in contrast to our previously thought, the anthropogenic discharge of trace metals did not adversely affect water quality. Our results indicate that dam construction in riverine systems attenuates trace metal contamination in water through sediment sorting and deposition.

Altitudinal-modulated sediment inputs rather than the land-uses determine the distribution of lead in the riparian soils of the Three Gorges Reservoir

Lead (Pb) as a toxic metal has potential ecological hazards for aquatic quality. However, the variation in the distribution patterns of Pb and its fractions in flooding soils with frequent and anti-seasonal water-level fluctuation and various human disturbances remains unclear. In this study, the distribution of Pb and its fractions in the riparian soils of the Three Gorges Reservoir (TGR) were delineated based on the differences in altitude and land-uses including farmland, orchard, forest and residential area. Then, we assessed the contamination and eco-risk of Pb in the soils and deciphered the key factors determining the distribution of Pb and its fractions. The results showed that the concentrations of Pb and its fractions in the soils decreased significantly with altitude, while the significant difference was not observed among the land-uses. The contamination of Pb in the soils reached a moderate level, and its eco-risk was very low by the potential eco-risk index and mobile Pb fraction. The source of soil Pb at the upper zone (> 160 m) was mainly from natural inputs, while the source at the lower zone (≤ 160 m) was attributed to anthropogenic contributions including ores mining, fossil fuel combustion, vehicle emissions and atmospheric deposition indicated by Pb isotopic ratios. With the limited effect of land-uses, the sediment inputs regulated by frequent water-level fluctuation determined the altitudinal distribution of Pb and its fractions in the flooding soils. The soil particle size dominated the migration and transformation of Pb over other soil properties such as pH and organic matters. The results of this study indicate that the anthropogenic Pb mainly exists in the soils of lower riparian zone in the TGR, and the frequent and anti-seasonal dry and rewetting alternation aggravates the potential for the Pb migration downstream due to the determinant of soil particles.

Spatiotemporal distribution of vanadium in the flooding soils mediated by entrained-sediment flow and altitude in the Three Gorges Reservoir

The re-emergence of vanadium (V) as a toxic metal has been highlighted recently due to its long-standing environmental and health hazard. This work targeted the world largest reservoir-Three Gorges Reservoir (TGR) to explore the spatial variation of V in the flooding soils from 2014 to 2018; meanwhile, the typical riparian zones with different altitudes and land-uses at the middle reach of the TGR were selected to decipher the key drivers on the V distribution. The results showed that the concentrations of soil V in the mainstream markedly exceeded local background, but they did not vary significantly with time except a marked increase at the upper-middle reaches. Spatially, the concentrations of soil V increased towards the dam, and the increase trend became increasingly significant with time. At the typical riparian zone, the concentrations of soil V decreased strikingly with altitude despite the difference in the land-uses, and a marked change-point occurred at 160-165 m. The soil V dominated by residual fraction, followed by oxidizable and reducible fractions, and then the minimal acid-soluble fraction. The contamination and eco-risk of V in the soils were low with similar spatiotemporal variation to its concentrations. Entrained-sediment flow and particle size rather than pH and organic matters led to the spatiotemporal variation in the distribution of soil V in the mainstream, and the driving effects tended to be more predominant with time. Altitude-regulated alteration of soil properties including particle sizes and iron/manganese (hydr)oxides with different flooding duration dominated the vertical distribution of V over the local land-uses at the riparian zone. Our results reveal the hotspots of V contamination in the riparian soils of the TGR and highlight unceasing focus on the variation in the distribution and dynamic migration of soil V due to its levels out of limits and changing soil conditions.