Cascade Hydropower Development Research Articles

The water resource efficiency and water-saving effect of cascade hydropower development

The water resource efficiency and water-saving effect of cascade hydropower development

Assessing the long-term impact of cascade hydropower development on the inundation patterns of floodplain wetlands

The inundation process of floodplain wetlands plays a crucial role in maintaining the balance of river ecosystems, which are highly sensitive to hydrological alteration. Nevertheless, the specific mechanisms through which these hydrological changes affect the inundation patterns of floodplain wetlands are still unclear. This study aimed to investigate the impact mechanism of cascade hydropower development on the inundation process of floodplain wetlands. Multitemporal remote sensing datasets and long-term hydrometeorological data series were utilized in this study. By employing the water appearance frequency (WAF) index, wetland hydrological stability assessment, and wavelet analysis, the inundation changes in floodplain wetlands and the underlying hydrological driving mechanisms were examined. The results revealed significant alterations in the inundation frequency of floodplain wetlands due to the construction of upstream dams. Specifically, the construction of the Danjiangkou and Wangfuzhou dams led to an increase in the total inundated area of Part A (16.09 km2) and Part B (76.93 km2), respectively. Conversely, the moderate frequency inundation zone in Part C decreased (26.7 km2) after the construction of the Cuijiaying Dam. The typical floodplain wetland 7 shifted from high to low (8.94 km2) stability after the construction of the Cuijiaying Dam. Furthermore, the cascade hydropower dam construction resulted in increased fluctuations in downstream water discharge. This study provides an effective approach to understanding the impact of cascade hydropower dams on the inundation process of floodplain wetlands.

Susceptibility Evaluation of Debris Flow Disaster in Plateau Hydropower Cascade Development Reservoir Area

The Rumei Hydropower Station is a typical cascade hydropower development project in a plateau area. The dam site is located in an area with complex topography, lithology, and geological structure. Geological disasters are developed in the area, mainly debris flow. Thus, taking the dam site and the surrounding areas as key evaluation objects, the engineering geological characteristics, geological environment characteristics, and the susceptibility and risk of geological disasters that may be caused are predicted and evaluated. The main methods used in this assessment are the binary logistic regression model and expert evaluation. The results show that the susceptibility to geological disasters is small and medium. The results of this study could provide a scientific basis for the rationality of the general layout and site selection of the project construction in the plateau water elevator level development reservoir area.

Biogeographic Distribution Patterns and Ecological Mechanisms of Benthic Eukaryotic Microorganisms in Jinsha River

Eukaryotic microbial communities play an important role in biogeochemical cycling and maintaining the health and stability of ecosystems. However, little is known about the geographical distribution patterns, key driving mechanisms, and interspecific interactions of eukaryotic microorganisms in large rivers. This study investigated the geographical distribution characteristics, influencing factors, and interspecific interactions of eukaryotic microorganisms in sediments from the Jinsha River, a cascade hydropower development river in southwest China. The results showed that the α-diversity indices of benthic eukaryotic microorganisms in the Jinsha River increased first and then decreased. The community structure and relative abundance of dominant genera of benthic eukaryotic microorganisms differed significantly among different reaches. The results of distance decay analysis showed that the community assembly of benthic eukaryotic microorganisms in the Jinsha River was influenced by environmental selection and dispersal limitation. The results of variance partitioning analysis and neutral model further demonstrated that the geographical distribution pattern was mainly driven by dispersal limitation. The co-occurrence network analysis revealed that the interspecific competition and network connectivity of the cascade dam reach were weaker than those of the upstream natural reach, indicating that the interactions of benthic eukaryotic microorganisms were stronger in the upstream natural reach. This study supplemented the lack of data on the diversity and geographical distribution of benthic eukaryotic microorganisms in the river of southwest China and provided data support for the ecological response of benthic eukaryotic microorganisms in the river of cascade hydropower development.

Heavy Metals Enrichment Associated with Water-Level Fluctuations in the Riparian Soils of the Xiaowan Reservoir, Lancang River.

The cascade hydropower development in the Lancang River has significantly modified the hydrologic regime and is consequently responsible for many local environmental changes. The influence of the altered hydrological regime on heavy metals accumulation in the soils of the riparian zone was evaluated for the Xiaowan Reservoir (XWR). Specifically, this study focused on investigating the trace metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn and their concentrations in the riparian soils. Furthermore, this research aimed to examine the contamination levels of heavy metals by employing the geoaccumulation index (Igeo) and the ecological risk index (RI), respectively. Additionally, the relationship between heavy metals and water level fluctuations as caused by the dam operation was explored. The results showed that heavy metals deposits occurred in relatively low levels in the riparian soils of XWR, even though several of these metals were revealed to occur in higher concentrations than the local background value. The Igeo assessment indicated that the riparian soils exhibited slight pollution by Hg at the Zhujie wharf (ZJW) and Cr at the transect of the Heihui River (HHR), and moderate contamination by As at ZJW. Moreover, the RI revealed that As in riparian soils is moderately hazardous while Hg poses a high risk at ZJW. The polluted water and sediments from upstream and upland of the riparian zone may be contributing to the changed concentrations of heavy metal in the riparian soils. The present study inferred that the WLFs due to reservoir impoundment play a vital role in the accumulation of trace metals in the riparian zone. However, more exhaustive investigations are necessary for verification.

Integrated flood risk assessment of river basins: Application in the Dadu river basin, China

Flood is the most common worldwide natural disaster with enormous impacts on human society and the ecosystem. Consequently, the research of flood risk assessment and zonation is critical. Its research scope is changeable, wherein the basin-scale research has become more and more important due to the increasing boom of cascade hydropower development in the river basin. The study proposed a basin-wide integrated flood risk assessment method combining index-based evaluation, Analytical Hierarchy Process (AHP) and Geographic Information System (GIS) technologies, which was implemented in the Dadu River basin, southwestern China to assess and zoning the basin flood risk. In the constructed risk assessment index system, we use extreme rainfall and dam breach to jointly describe the basin flood disaster-inducing factors and select flood control standard and flood routing coefficient as the sub-indicators of basic and specific coping capacity to characterize the flood intervention capacity of hydropower engineering. The results showed that, for the hazard, vulnerability and risk zonation maps with five classified levels, the southern of midstream and downstream of the basin are prone to frequent floods, while higher vulnerability levels mainly concentrate in the downstream but some parts scatter in the medium vulnerability zone. The high and very high risk zones account for 3% of the basin area and mainly concentrate in the southern basin, while 86% of the basin area is assigned as low and very low risk zones. The results of this work quantitatively express the spatial distribution characteristics of basin-wide flood hazard, vulnerability and risk, and provide a reference for practicing an integrated and efficient flood risk management, and disaster prevention and alleviation strategies.

Influence of Cascade Hydropower Development on Water Quality in the Middle Jinsha River on the Upper Reach of the Yangtze River

In recent decades, there has been unprecedented development of hydropower in China, especially in the Yangtze River Basin, which has changed the hydrological and hydraulic conditions of natural rivers and has an impact on water quality. However, the spatial-–temporal extent, factors, and the reasons behind the influence of cascade hydropower development are not clear. The six hydropower stations on the main course of the middle reach of the Jinsha River in Yunnan and Sichuan Provinces have been in joint operation for seven years, and the impact of cascade hydropower development on water quality has begun to appear. In this paper, in order to accurately determine the causal relationship between cascade hydropower development and water quality changes on the middle reaches of the Jinsha River and their trends using regression discontinuity analysis, we collected monitoring data on water quality from 2004 to 2019. The results show that cascade hydropower development on the middle reach of the Jinsha River led to a decrease in TP concentration in that section of the river and an increase in the concentration of CODMn and NH3-N. Furthermore, increase in sedimentation following the impoundment of cascade hydropower development is the main reason for the decrease in TP concentration, and the regional economic and social development driven by cascade hydropower development are external sources of the increase in the concentration of CODMn and NH3-N. In addition, influenced by rainfall, the concentrations of CODMn and TP are higher in the rainy season and lower in the dry season, which is directly related to the input of non-point-source pollutants in the basin during the former. This study established a model to accurately judge the causal relationship between cascade hydropower development and water quality changes in the basin, which was then used to assess the impact of cascade hydropower development on water quality. Our results provide a basis for the formulation and implementation of a water quality protection plan for the middle reach of the Jinsha River and can also provide a basis for the development of cascade hydropower in other river basins.

Effects of cascade dams on the occurrence and distribution of microplastics in surface sediments of Wujiang river basin, Southwestern China

The influence of cascade dams on the migration of microplastics (MPs) was conducted by analyzing the spatial distribution of MPs in sediments of the Wujiang river basin (Wujiang river basin) in Southwest China. The results showed that the abundance of MPs in Wujiang river basin sediments ranged from 310 to 2620 items/kg dw (mean: 1354 items/kg dw, a high level compared with aquatic sediments worldwide). The main chemical components of these MPs were polypropylene and polyethylene. High abundance of MPs in tributary sediments suggested that tributary inputs contributed to the main stream and reservoirs. Statistical analysis showed that gross domestic product (GDP) and the basin area of cascade reservoirs, rather than hydraulic retention time and reservoir age, were the dominating factors in the distribution of MPs in the Wujiang river basin. The accumulation of MPs in cascade reservoirs implied the interception effect of cascade dams. The rapid development of cascade dam systems and the interception effect of dams should be taken into account when predicting the flux of MPs from rivers to the ocean. Heavy metals found on the surface of the MPs showed the compound pollution of MPs and heavy metals in dammed rivers and cascade reservoirs. Our results deepen the understanding of the migration of MPs in rivers alongside intensive cascade hydropower development.

Emergy theory to quantify the sustainability of large cascade hydropower projects in the upper Yangtze

Cascade development of hydropower projects in a river basin can fully enhance the utilization of hydropower resources. Yet, the impacts of cascade hydropower projects on river ecosystems and social-economic systems are not well elaborated. The current research proposed an emergy estimation method to evaluate the environmental sustainability of two large hydropower projects and suggest the reasonable scale of hydropower development at river basin scale. Unlike traditional approach that used a single hydropower project as a system, the method took river reach as a system. The cascade hydropower development in lower Jinsha River, the river reach in the upper Yangtze River in China, were taken as the case study to apply the method. The results shown that at current level of construction and management, the development of Xiangjiaba and Xiluodu are still sustainable but insufficient. And the scale of large hydropower development in the lower reaches of the Jinsha River is suggested to be 29000 MW to 54000 MW. Then the transformity of hydroelectricity would be 9.50E+04seJ/J to 6.85E+04seJ/J. The Emergy sustainability indicator (ESI) decreases with the increasing of development scale, ESI would be 6.5 in the case of current development plan (45200MW), which means a good utilization efficiency and sustainability. However, the on-grid electricity price was suggested to increase to 0.40 CNY/kW•h for the reason that fair price of the electricity is higher than the on-grid electricity price. Such evaluation results could have a greater reference for hydropower planning in river basin. We believed that this approach can help policymakers and stakeholders make more reliable decisions in hydropower planning.

Spatially-explicit quantitative relationship for a potential PES mechanism: Cascade hydropower development in Yarlung Zangbo River Basin, China

Spatially-explicit quantitative relationship for a potential PES mechanism: Cascade hydropower development in Yarlung Zangbo River Basin, China

Migration characteristics of arsenic in sediments under the influence of cascade reservoirs in Lancang River basin

Cascade hydropower development in the Lancang River (LCR) Basin has a complex and far-reaching impact on river ecosystem, which has always been the focus of international attention. In this study, diffusive gradients in thin films (DGT) technique was used to study the reactivation of arsenic (As) in the sediments of Xiaowan (XW) and Nuozhadu (NZD) cascade dams in LCR. Pearson correlation analysis and Redundancy Analysis (RDA) were used to evaluate the bioavailability and spatial distribution characteristics of As. The results showed that the vertical variation of As in DGT at different sampling points presented different activation trends. The content of DGT-labile As (CDGT-As) in NZD Reservoir (36.21 ng/ml) was less than that in XW Reservoir (47.26 ng/ml). However, the difference of total content of As between the two reservoirs was relatively small. The results showed that the development of cascade reservoirs had no significant impact on total As, but had a great impact on DGT-labile As. The diffusion fluxes of the two reservoirs indicated that most of the sediments in the reservoir area were the source of As. Similar distribution characteristics and correlation analysis indicated that the migration mechanism of As was related to Iron (Fe) and manganese (Mn). In addition, on the basis of the results, the sources of As in sediments had certain spatial differences: cascade dam projects had significant accumulation and interception effects on As in the sediments, and at the same time strengthened the role of regional sediment, and this role reduced the risk of As release in downstream NZD Reservoir.

Experimental study of the degasification efficiency of supersaturated dissolved oxygen on stepped cascades and correlation prediction model

Spills of dams often lead to dissolved gases supersaturation of water downstream. Owing to the slow dissipation, the impact of supersaturated dissolved gases in cascade hydropower development basin may be basin-wide, which can cause fish mortality. It is imperative to explore high-efficiency technology to reduce the saturation of dissolved gases. Stepped cascades are recognized as high potential air-water mass transfer exchangers, their application focused on re-oxygenation. In the literature, stepped cascades weren't applied in the dissipation of supersaturated dissolved gases yet. In this study, 89 groups of supersaturated dissolved oxygen degassing experiments were carried out in three different types of stepped cascades. From the top to the bottom of stepped cascades, supersaturated dissolved oxygen dissipated rapidly and the most significant drop was 63.3%. Degasification efficiency was defined by the percent saturation of dissolved oxygen measured on different steps and the equilibrium saturation. The variation law of degasification efficiency of supersaturated dissolved oxygen was discussed under different flow regimes. The degasification efficiency showed a positive relation with energy dissipation efficiency and the length of aerated flow region. Then a correlation model to predict the degasification efficiency was established with which the square of the correlation coefficient (R2) between calculated and experimental values is 0.93. Finally, two possible applied scenarios of stepped cascades in natural rivers were listed, the model was proved practical. The results of this study can provide suggestions for the construction, operation and management of hydropower development considering ecological-environmental protection.

The Impact of Cascade Large Deep Reservoir on the Migration and Deposition of Cadmium in Lancang River

Metal pollution is a global environmental problem. In order to understand the effects of the cascade hydropower development on Cd in reservoir sediments, this study investigated the migration and deposition mechanisms of Cd in reservoir sediments by using the film diffusion gradient technique (DGT) for the cascade large deep reservoirs of the Lancang River (LCR), Nuozhadu (NZD) and Xiaowan (XW). The results show that: (1) Strong correlations amongst the deposition processes of Cd, Mn and S were found in the sediments of the NZD reservoir; weak correlations between the deposition processes of Cd and Mn were found in the sediments of the XW reservoir. (2) Part of labile Cd in the pore water of the NZD reservoir was supplemented by silt and sand, and another part was inherent in the pore water; most of labile Cd in the pore water of the XW reservoir was inherent in the pore water, and minimal replenishment of sediment was noted. (3) Mn is the main factor controlling the migration of Cd in the NZD reservoir. This paper provides an effective resource for understanding the migration and deposition of Cd in the sediments of large deep reservoirs along the LCR.

Spatial-temporal dynamics and influencing factors of archaeal communities in the sediments of Lancang River cascade reservoirs (LRCR), China.

The spatial and temporal distribution of the archaeal community and its driving factors in the sediments of large-scale regulated rivers, especially in rivers with cascade hydropower development rivers, remain poorly understood. Quantitative PCR (qPCR) and Illumina MiSeq sequencing of the 16S rRNA archaeal gene were used to comprehensively investigate the spatiotemporal diversity and structure of archaeal community in the sediments of the Lancang River cascade reservoirs (LRCR). The archaeal abundance ranged from 5.11×104 to 1.03×106 16S rRNA gene copies per gram dry sediment and presented no temporal variation. The richness, diversity, and community structure of the archaeal community illustrated a drastic spatial change. Thaumarchaeota and Euryyarchaeota were the dominant archaeal phyla in the sediments of the cascade rivers, and Bathyarchaeota was also an advantage in the sediments. PICRUSt metabolic inference analysis revealed a growing number of genes associated with xenobiotic metabolism and carbon and nitrogen metabolism in downstream reservoirs, indicating that anthropogenic pollution discharges might act as the dominant selective force to alter the archaeal communities. Nitrate and C/N ratio were found to play important roles in the formation of the archaeal community composition. In addition, the sediment archaeal community structure was also closely related to the age of the cascade reservoir and hydraulic retention time (HRT). This finding indicates that the engineering factors of the reservoir might be the greatest contributor to the archaeal community structure in the LRCR.

DNA barcoding for identification of fishes in Xiangjiaba reservoir area in the downstream section of the Jinsha river

The downstream section of the Jinsha River is a global biodiversity hotspot for fishes. However, cascade hydropower development has altered the original habitat and has had a huge impact on the area’s fish diversity. To assess the power of DNA barcoding and construct a DNA barcode library for Xiangjiaba reservoir area, 333 fish mitochondrial DNA barcodes (672 bp) employing a fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI) were obtained for 57 species from the Xiangjiaba reservoir area in this study. The intra-specific genetic distances were below 2%, ranging from 0 to 1.69% (mean 0.19%). The interspecific genetic distances within genera ranged from 0.45 to 11.14% (mean 2.98%). The Bayesian inference (BI) tree and neighbor-joining (NJ) tree inferred that all species were unambiguously separated, with strong support values at the terminal branches except the node of Hemibarbus maculatus shared with its adjacent clade. The DNA barcoding gaps could accomplish fish species discrimination. These results revealed that DNA barcoding was an effective tool for the identification of fish species, and that it was possible to construct a robust DNA barcode reference library for fish species in the Xiangjiaba reservoir area. The results will contribute to future efforts in monitoring, conservation, and management of fish resources.

水电梯级开发进程中澜沧江干流鱼类群落演变特征

水电梯级开发进程中澜沧江干流鱼类群落演变特征

Do bacterioplankton respond equally to different river regulations? A quantitative study in the single-dammed Yarlung Tsangpo River and the cascade-dammed Lancang River

River damming has raised controversial concerns as it simultaneously contributes to socioeconomic development but may jeopardize aquatic ecology. Since bacterioplankton catalyze vital biogeochemical reactions and play important roles in aquatic ecosystems, more attention has been paid to their responses in dammed rivers. Here, a comparative study was conducted between single-dammed (the Yarlung Tsangpo River) and cascade-dammed (the Lancang River) rivers in Southwest China to investigate whether bacterioplankton respond equally to different river regulations. Our results showed that the decreased bacterioplankton abundance and the increased α-diversity always co-occurred in reservoirs of the Yarlung Tsangpo River and the Lancang River. However, the impact of damming on bacterioplankton abundance and α-diversity were resilient in the Lancang River, which can be attributed to the repeated alterations of environmental heterogeneity in cascade damming reaches. Meanwhile, a generalized additive model (GAM) was applied to identify the important drivers affecting bacterioplankton variation. The abundance was influenced by trophic conditions, such as dissolved silicon, while α-diversity was closely related to the microbial dispersal process, such as elevation and distance-from source. And it is also noted that the bacterioplankton dispersal process was interrupted in cascade damming reaches. In addition, based on their important drivers, variations in abundance and α-diversity were also predicted by GAM. As revealed by the quantitative mutual validation between the two rivers, abundance and α-diversity in the cascade-dammed river can be predicted by their response to single-dammed river, suggesting that the impact of cascade damming on bacterioplankton can be pre-assessed by referring to the single stage damming effect. Therefore, our study provides the first trial of quantitative evidence that bacterioplankton do not respond equally to different river regulations, and the impact of cascade damming on bacterioplankton can be predicted based on single stage damming effect, which can contribute to the protection of aquatic ecology in the cascade hydropower development.

Morphological changes in the lower Lancang River due to extensive human activities.

BackgroundMorphological changes in river beds determine the risk for soil erosion within floodplain areas. At present, little is known about river morphological changes in high-altitude mountainous area influenced by extensive human activities. The study has important reference value for clarifying the morphological changes of mountainous rivers due to extensive human activities.MethodsBased on the long-term multi-source remote sensing image data, we analyzed morphological changes in the lower Lancang River (LCR) in Southwest China at regional and local scales, and determined their influencing factors. Visual interpretation is used to extract the information and unify the interpretation standards of various localities, mainly including water bodies, sandbars, shorelines and beaches. Based on high-resolution remote sensing images, we analyzed the planforms, erosion and accretion conditions in Jinghongba (JHB) reach and Ganlanba (GLB) reach.ResultsOur results showed that: (1) during 1993–2016, the planforms of Jinghongba and Ganlanba in the wide valley of the lower LCR changed significantly, (2) In the interval 1993 to 2016, the JHB reach exhibited extensive erosion, with the right bank more eroded seriously than the left bank, and an erosion area of 0.36 km2. The erosion area of the GLB reach was 0.33 km2, with accretion area of 0.61 km2. The right bank was dominated by erosion, while the left bank by sedimentation; (3) Morphological changes in JHB and GLB reches were the result of the combined effects of cascade hydropower development, river regulation, and sand-mining in the river. The results improved the understanding of riverbed evolution, and could help guide sediment management in mountainous areas influenced by extensive human activities.

The influence of cascade hydropower development on the hydrodynamic conditions impacting the reproductive process of fish with semi-buoyant eggs

Hydropower projects have changed the physical habitat of rivers, which has a serious impact on the survival of local fish. The reproduction of fish producing semi-buoyant eggs requires a specific hydrodynamic condition. To predict the influence of cascade hydropower development on the reproductive process of fish with semi-buoyant eggs, a MIKE 21 Flow Model was applied. Lagrangian particle tracking was used to simulate the movement of semi-buoyant eggs and larvae using the Agent-based Modeling (ABM) lab module. The calibrated model showed good agreement between the simulated and observed data for the hydrodynamic process in the reservoir. Twelve scenarios were defined to fully understand whether fish with semi-buoyant eggs can reproduce naturally. The results showed the following: (1) It is difficult to form a fish migration passage in the reservoir in all potential scenarios. (2) Semi-buoyant eggs and larvae sank to the bottom and perished before they hatched and were old enough to survive, since the hydrodynamic conditions could not meet the minimum flow velocity required to keep them in the drift. (3) Even if the hydrodynamic conditions can keep them in the drift in impossible high-discharge conditions, there was not enough drifting time and distance in the reservoir. The results implied that fishes with semi-buoyant eggs cannot reproduce naturally in the main stream, but it is possible that they can reproduce successfully after the protection of the tributary. The method is transferrable to other locations via establishment of models with relevant data to a particular area.

Time Series Decision-making of Cascade Hydropower Station Development Based on Prospect Theory

To make a reasonable decision on the development timing of cascade hydropower stations, the optimal dispatching model and prospect theory are synthetically applied to establish a development timing decision model based on psychological preference. First, according to the characteristics of hydropower benefit development, the influence of generation capacity and minimum output on development benefit is analyzed, and the mechanism of the decision maker’s psychological change is clarified. Second, the double-objective dispatching benefit preference function is proposed and the variable weight theory is introduced to modify the probability decision weight. Finally, the optimal genetic algorithm used to solve the dispatching scheme and calculate the pre-synthesis weights. Scene value is used to analyze the effect of preference of different reference points on decision-making. The case study indicated that the A scheme should be selected when considering the overall balance and economy of the system, the C scheme should be chosen when the decision maker prefers maximum power generation, and the B scheme should be chosen when the decision maker prefers the output. Compared to the traditional decision-making evaluation, the influence of the decision maker's preference on the development sequence is further verified, which provides a theoretical basis for the study of cascade hydropower development decision-making under different preferences.