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3 results on '"water-sediment dynamics"'

1. Mega-reservoir regulation: A comparative study on downstream responses of the Yangtze and Yellow rivers.

Author

Wu, Xiao, Yue, Yao, Borthwick, Alistair G.L., Slater, Louise J., Syvitski, Jaia, Bi, Naishuang, Yang, Zuosheng, and Wang, Houjie

Subjects
*EROSION, *RESERVOIR sedimentation, *WATERSHEDS, *SEDIMENT transport, *ALLUVIAL streams, *COASTAL sediments, *RIVER channels
Abstract

Large reservoirs can considerably alter the water-sediment dynamics and morphology of alluvial rivers. Here we review the effects of two mega reservoirs operated with different regulation modes. The Three Gorges Reservoir (TGR) on the Yangtze River has a typical anti-seasonal regulation mode, while the Xiaolangdi Reservoir (XLDR) on the Yellow River undergoes a swift drawdown process shortly before the flood season through the Water and Sediment Regulation Scheme (WSRS). We examine the influence of these regulation schemes on downstream water-sediment dynamics and find that vast sedimentation occurred in both the TGR (128.4 Mt./yr) and XLDR (210.2 Mt./yr). The two rivers have experienced different changes in downstream sediment transport capacity, with coincident flood and sediment peaks in the Yangtze River but with sediment peaks lagging behind flood flow peaks in the Yellow River. On the Yangtze River, highly unsaturated flows from the TGR led to widespread incision downstream, while on the Yellow River, such flows did not induce significant erosion in the first two years following impoundment. The low annual runoff and high sediment yield of the Yellow River mean that riverbed erosion occurred mainly when the water discharge and sediment transport capacity were enhanced by the WSRS. In both rivers, the riverbed eroded and coarsened downstream of the mega dams, lowering the dry season water level. The increase in channel roughness maintained or even raised flood season water levels, potentially increasing flood risk. Sediment budgets reveal that the river segments downstream of the dams switched from sediment sinks to sources due to riverbed incision. Despite new supply from downstream reaches, sediment deficits arising from dam interception and other human activities within the drainage basins have posed significant challenges to the sustainability of the Yangtze and Yellow river deltas, resulting in lower accumulation rates or even transition from progradation to degradation in subaqueous areas. In contrast to the anti-seasonal regulation mode of the TGR, the WSRS of the XLDR has proven very effective at mitigating reservoir sedimentation and has boosted the quantity of sediment reaching the sea, facilitating delta stability and coastal sediment replenishment. [ABSTRACT FROM AUTHOR]

Published
2023
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2. Water-Sediment Physicochemical Dynamics in a Large Reservoir in the Mediterranean Region under Multiple Stressors

Author

Maria Helena Novais, Maria João Costa, Miguel Potes, Clarisse Mourinha, Paula Alvarenga, Maksim Iakunin, Ana Lima, Manuela Morais, Anabela Rosado, Sofia Fialho, Rui Salgado, Gonçalo C. Rodrigues, Patrícia Palma, and Alexandra Marchã Penha

Subjects
Mediterranean climate, lcsh:Hydraulic engineering, Water-sediment dynamics, 010504 meteorology & atmospheric sciences, Geography, Planning and Development, Land cover, 010501 environmental sciences, Aquatic Science, 01 natural sciences, Biochemistry, Water scarcity, Ecosystem services, lcsh:Water supply for domestic and industrial purposes, Water column, lcsh:TC1-978, Climate variability, 0105 earth and related environmental sciences, Water Science and Technology, lcsh:TD201-500, Land use, Alqueva reservoir, Land cover/ land uses, Water resources, Environmental science, Water resource management, Eutrophication
Abstract

Nowadays, the Mediterranean freshwater systems face the threat of water scarcity, along with multiple other stressors (e.g., organic and inorganic contamination, geomorphological alterations, invasive species), leading to the impairment of their ecosystem services. All these stressors have been speeding up, due to climate variability and land cover/land use changes, turning them into a big challenge for the water management plans. The present study analyses the physicochemical and phytoplankton biomass (chlorophyll-a) dynamics of a large reservoir, in the Mediterranean region (Alqueva reservoir, Southern Portugal), under diverse meteorological conditions and land cover/land use real scenarios (2017 and 2018). The most important stressors were identified and the necessary tools and information for a more effective management plan were provided. Changes in these parameters were further related to the observed variations in the meteorological conditions and in the land cover/land use. The increase in nutrients and ions in the water column, and of potentially toxic metals in the sediment, were more obvious in periods of severe drought. Further, the enhancement of nutrients concentrations, potentially caused by the intensification of agricultural activities, may indicate an increased risk of water eutrophication. The results highlight that a holistic approach is essential for a better water resources management strategy.

Published
2021
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3. Water-sediment physicochemical dynamics in a large reservoir in the Mediterranean region under multiple stressors

Author

Palma, Patrícia, Penha, Alexandra Marchã, Novais, Maria Helena, Fialho, Sofia, Lima, Ana, Mourinha, Clarisse, and Alvarenga, Paula

Subjects
climate variability, water-sediment dynamics, Alqueva reservoir, land cover/land uses
Abstract

Nowadays, the Mediterranean freshwater systems face the threat of water scarcity, along with multiple other stressors (e.g., organic and inorganic contamination, geomorphological alterations, invasive species), leading to the impairment of their ecosystem services. All these stressors have been speeding up, due to climate variability and land cover/land use changes, turning them into a big challenge for the water management plans. The present study analyses the physicochemical and phytoplankton biomass (chlorophyll-a) dynamics of a large reservoir, in the Mediterranean region (Alqueva reservoir, Southern Portugal), under diverse meteorological conditions and land cover/land use real scenarios (2017 and 2018). The most important stressors were identified and the necessary tools and information for a more effective management plan were provided. Changes in these parameters were further related to the observed variations in the meteorological conditions and in the land cover/land use. The increase in nutrients and ions in the water column, and of potentially toxic metals in the sediment, were more obvious in periods of severe drought. Further, the enhancement of nutrients concentrations, potentially caused by the intensification of agricultural activities, may indicate an increased risk of water eutrophication. The results highlight that a holistic approach is essential for a better water resources management strategy info:eu-repo/semantics/publishedVersion

Published
2021

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