Impoundment Of Three Gorges Dam Research Articles

Joint impacts of dams and floodplain on the rainfall-induced extreme flood in the Changjiang (Yangtze) River

Fluvial flooding is the most devastating natural hazard in the world, which presents an increased trend in the context of global warming and the active hydrological cycle with large risk for human survival. In 2020, a historically extraordinary flood hit the Changjiang River Basin where located considerable mega dams and reservoirs, including the world’s largest dam, Three Gorges Dam (TGD). The 2020 extreme flood raises public concern about the effectiveness of the impoundment of dams and reservoirs on flooding. Here, we analyzed the observed water discharge and level during the extreme flood in 2020 as well as the simulated rainfall-induced discharge and level data through the GR4J model and level-discharge curve. Results show that the water levels exhibited a rapid response to the increased water discharge, and exceeded the warning level at almost the same time along the middle and lower reach during the 2020 extreme flood. The intensive rainfall caused the basin-wide extreme flood with extra regional rainwater responsible for the largest flood in the middle and lower reach. Dams and reservoirs significantly mitigated the extreme flood by reducing 1.49 m in the flood levels and contributing to 94 % of the level changes. Meanwhile, the TGD impoundment successfully prevented a disastrous flood that could have happened with the flood level being lowered by 2.93 m. However, the considerable recession of the downstream floodplain amplified the flood level by 0.08 m, which was equal to increasing the total flood level by 5 %. Our results highlighted the crucial role of mega dams in flood control and the potential of restored floodplain storage for sustainable flood modulation in the future.

Reshuffling of the sediment suspension regime in the “starving” middle Yangtze River downstream from cascade mega-reservoirs

The impoundment of cascade mega-reservoirs in the upper Yangtze River (uYR) has exerted profound and accumulative impacts on the lower reaches—not only a drastic drop in the incoming sediment load but also overturning of the runoff-sediment relationship. Based on a 1990–2021 dataset, we examined fundamental changes in the sediment suspension regime in the Jingjiang reach, approximately 100 km below the Three Gorges Dam (TGD). The cascade mega-reservoir impacts are elucidated by three parameters: inflow water discharge and sediment concentration released to the Three Gorges Reservoir (TGR) and operating water levels in front of the TGD. The wash-load concentrations in the reach in the post-TGR period illustrate strong relationships with the flow capacity index, they, however, were actually determined by the above three parameters. The relative importance of the three parameters in determining the wash-load concentrations was evaluated by a random forest model. After upstream reservoir impoundment starting in 2003, the unsaturation degrees in the reach tended to increase, and the thresholds distinguishing wash-load and bed-material-load have risen to ∼0.125 mm and ∼0.25 mm at SS/JL and ZC after TGD impoundment, respectively. In addition, the flow capacity coefficients, i.e., m and k, in the “starving” reach became significantly lower than their equilibrium counterparts. The study aims to facilitate effective management of the uYR cascade mega-reservoirs and the experience could be drawn on for other large rivers facing hydropower development.

Three Gorges Dam Operation Altered Networks of Social–Economic–Ecological System in the Yangtze River Basin, China

It is necessary to review changes in the interactions of indicators following the construction of the Three Gorges Dam (TGD) in order to explore the impact of the dam on ecology. Research on changes in interactions among indicators of the comprehensive social–economic–ecology system in the Yangtze River Basin is limited, and the objective of this study was to investigate how this system changed after the operation of the TGD, as well as how the indicators contributed to this change. Here, the correlational network approach using 38 data point indicators from 1949 to 2018 of the Yangtze River Basin was applied to analyze the changes in indicator interactions before and after the TGD operation. The TGD impoundment altered networks of the social–economic–ecological system in the Yangtze River Basin. Indicators are both less positively and less negatively connected. The number of synergy and trade-off networks clusters changed from two (Modularity = 0.33) to -six (Modularity = 0.23) and from two (Modularity = 0.015) to four (Modularity = 0.34) after the TGD operation, indicating that the sustainable development of the Yangtze River Basin might be at a middle level after the TGD operation. Further analysis revealed that the mean annual discharge, downstream fry runoff, and downstream counts of the eggs and larvae of four carp, diatom abundance index, breeding population of Chinese sturgeon, and annual precipitation contributed more to the changes in the networks after 2003.

Precipitation Changes in the Three Gorges Reservoir Area and the Relationship with Water Level Change

As the largest hydroelectric project worldwide, previous studies indicate that the Three Gorges Dam (TGD) affects the local climate because of the changes of hydrological cycle caused by the impounding and draining of the TGD. However, previous studies do not analyze the long-term precipitation changes before and after the impoundment, and the variation characteristics of local precipitation remain elusive. In this study, we use precipitation anomaly data derived from the CN05.1 precipitation dataset between 1988 and 2017 to trace the changes of precipitation before and after the construction of the TGD (i.e., 1988–2002 and 2003–2017), in the Three Gorges Reservoir Area (TGRA). Results showed that the annual and dry season precipitation anomaly in the TGRA presented an increasing trend, and the precipitation anomaly showed a slight decrease during the flood season. After the impoundment of TGD, the precipitation concentration degree in the TGRA decreased, indicating that the precipitation became increasingly uniform, and the precipitation concentration period insignificantly increased. A resonance phenomenon between the monthly average water level and precipitation anomaly occurred in the TGRA after 2011 and showed a positive correlation. Our findings revealed the change of local precipitation characteristics before and after the impoundment of TGD and showed strong evidence that this change had a close relationship with the water level.

Declining Sediment Discharge in the Yangtze River From 1956 to 2017: Spatial and Temporal Changes and Their Causes

AbstractA sharp decline in the Sediment load at the seaward most Datong station (DTS) of the Yangtze River occurred at an average rate of 7.22 × 106 t/yr since 1956, and this drop had a staircase pattern that can be divided into five distinct periods (1956–1968, 1969–1991, 1992–2002, 2003–2012, and 2013–2017). In this study, a new holistic basin‐wide Sediment Budget Method (SBM) was developed using sediment data from a total of 74 gauging stations (arguably the largest datasets so far) to estimate the sediment contributions to DTS from tributaries and mainstream. Our results show that the Jinsha River in upper basin between Panzhihua and Xiangjiaba used to be one of the largest contributors to DTS in 1956–2002 (16%–33%), but its contribution decreased sharply after 2003 due to the impoundment of Three Gorges Dam (TGD) and decreased further to nearly nil in 2013–2017 due to the impoundment of new cascade dams (CDs) which were upstream of TGD. In contrast, the mainstream between Yichang and Datong contributed 50%–64% of the DTS in 2003–2017, owing to the active channel erosion downstream of TGD. Before 2003 about 66%–84% of the DTS was contributed by the upper reach, but 72%–91% of the DTS was from the middle‐lower reaches after 2003, reflecting a drastic shift in sediment suppliers from upper to middle‐lower reaches. On average, the drop of DTS was 128.37 × 106 t/yr due to TGD impoundment in 2003–2012 and 27.28 × 106 t/yr due to CDs impoundment in 2013–2017 because of the reservoir trapping and the inhibition of historically eroding channels in the reservoir area. This new SBM can be applied to other large and small rivers around the world to track sediment sources/sinks and provide valuable results for sediment resource management.

Hydrological Drought in Dongting Lake Area (China) after the Running of Three Gorges Dam and a Possible Solution

Dongting Lake is located at the downstream of Three Gorges Dam (TGD) and the hydrological drought is intensified after the impoundment of TGD as the dry period has been extended from 123 days/year before the operation of TGD (1981–2002) to 141 days/year (2003–2016) on average. Particularly, the Dongting Lake’s water shortage becomes very severe. To solve the problem caused by upstream dams, an innovative flood control scheme (IFCS) was introduced, and its feasibility of application in Dongting Lake is studied using the hydrodynamic module of Mike 21. The results show the IFCS can effectively convert the peak discharge of floodwater in wet seasons into water resources in dry seasons as the IFCS could significantly increase the usable water storage of the lake. For example, the usable water storage could increase to 2.85 billion m3 and 1.81 billion m3 in the extreme drought year of 2006 and 2011, respectively. The average increment of the water level would be about 0.4 m, 0.6 m, and 0.5 m in the West Dongting Lake (WDL), South Dongting Lake (SDL), and the East Dongting Lake (EDL), respectively, if the water stored in the inner lake was discharged uniformly in 30 days (27 November to 27 December 2006) with the application of IFCS. This study may provide an innovative method to alleviate the water shortage problem in Dongting Lake and other similar lakes.

How the three Gorges Dam affects the hydrological cycle in the mid-lower Yangtze River: a perspective based on decadal water temperature changes

Three Gorges Dam (TGD), the world’s largest hydroelectric project in terms of installed capacity, alters the discharge and thermal regime of the Yangtze River in China, thereby threatening the aquatic biodiversity along the mid-lower Yangtze River. Thus, the influence of the TGD impoundment on the river temperature (Tw) and water cycle warrants in-depth examination. To the best of our knowledge, this study is the first to use decadal (2001–2013) Moderate Resolution Imaging Spectroradiometer temperature data to assess the impacts of TGD impoundment on the inland water cycle. We found that (1) spatially, the multiyear Tw decreased by 5 °C along the mid-lower Yangtze River, (2) temporally, Tw exhibited a warming trend after the operation of the TGD began, with most warming occurring from October to December directly after the TGD impoundment, and (3) the correlations between discharge and Tw in the pre- and post-TGD periods have changed; specifically, the closer to the TGD a location is, the greater the change in the relationship. Our analysis implies that downstream water temperature alteration is mainly attributed to the TGD management regime, and the influence is obvious along the 260 km river downstream of the TGD. It is likely that the impoundment of the TGD has increased the water residence time and slowed the water speed downstream.

Effects of Early Dry Season on Habitat Suitability for Migratory Birds in China’s Two Largest Freshwater Lake Wetlands after the Impoundment of Three Gorges Dam

Dongting Lake and Poyang Lake, the China’s two largest freshwater lakes, are the most important wintering area and pathways for migratory birds in East Asia. As a result of human activities (impounding of the Three Gorges Dam (TGD), and sand mining) and climate change, the dry season of Dongting Lake and Poyang Lake came early after the impoundment of TGD. And the early dry season (EDS) would change wildlife habitat and would have a negative effect on biology and biodiversity. In this paper, we compared the habitat suitability for Anatidae, Charadriidae, Ardeidae and Laridae (the four main types of migratory birds) of the Dongting Lake and Poyang Lake between three normal hydrologic years (NY) and three hydrologic years which had EDS (EY) of each lake by geo-spatial overlay calculation, to reveal the effect of EDS on the habitat suitability for the main types of migratory birds. The grading systems of suitability included four grades: poor (0-25), fair (25-50), good (50-75), and very good (75-100). The results showed that the EDS 1) improved the habitat suitability for Anatidae; 2) had no significant influence on the habitat suitability for Charadriidae and Ardeidae; and 3) had an almost significant adverse effect (would be significant in fact and in the future) on the habitat suitability for Laridae at the two wetlands.

GRACE observed mass loss in the middle and lower Yangtze basin

Anthropogenic architectures have a significant impact to the environment. The Three Gorges Dam (TGD), as the largest dam in the world, is a typical example, and has influenced the mass anomalies transported by the flow downstream in the Yangtze River since June 2003. However, the evidence of TGD influence on downstream mass transportation is not documented. In this study, we analyze the monthly gravity solutions from GRACE to investigate the downstream mass variations of Yangtze River. From our results, the considerable mass loss is detected in the downstream of TGD. By comparing our estimations with the in situ water level data of TGD, we find that the mass variations derived from GRACE at Datong station decreases shortly after the impoundment of TGD. This confirms a strong connection between them. Furthermore, by comparing with the in situ sediment load and river discharge at Yichang and Datong gauging stations, we find that the sediment load data shows a similar mass loss signature while the river discharge of both stations has stay at a relative stable level. This indicates that further study is still needed to understand the mechanism better.

Response of the Changjiang (Yangtze River) water chemistry to the impoundment of Three Gorges Dam during 2010–2011

The environmental impact of Three Gorges Dam (TGD) in the Changjiang (Yangtze River) is an important topic of concern for scientific communities and the public. However, the changes in river water chemistry in response to the dam construction remain poorly constrained. This study presents the seasonal variability of all major cations and some anions in the lower Changjiang during a full hydrological year from 2010 to 2011. The concentrations of all ions, except for HCO3−, are higher after the TGD operation than before (p < 0.01), implying that the TGD has modified the river water chemistry in the mid-lower mainstream. Dissolved silicate (DSi) fluxes at Datong station thus increase slightly since the beginning of TGD impoundment. The change of mixing pattern of different water sources and alteration of hydrological and biogeochemical processes could cause the change of solute concentrations in the mid-lower Changjiang after the TGD operation. The mass balance model suggests that two factors primarily account for this increase of DSi observed at Datong: 1) an increasing loading of DSi downstream TGD due to erosion by “clean water”, and 2) an enhanced “Source” role of Lake Poyang in the mid-lower reaches. Our study would provide insights into the damming effect on river water chemistry and the complexity of a large river system facing rapid climate change and strong human activities.

Remote observation of water clarity patterns in Three Gorges Reservoir and Dongting Lake of China and their probable linkage to the Three Gorges Dam based on Landsat 8 imagery

The Secchi disk depth (ZSD) plays a critical role in describing water clarity. Several studies have shown linkages between Three Gorges Dam (TGD) and the downstream lacustrine ecosystem in the middle and lower Yangtze River basin. However, the potential influence on the ZSD fluctuation in the entire anthropogenic reservoirs of Three Gorges (ER) and Dongting Lake (DTL) has not been reported, possibly due to technical obstacles in obtaining statistically significant spatial and temporal results. We addressed this challenge by using remote sensing technology: the Landsat 8 Operational Land Imager (OLI). We proposed a new, robust remote-sensing algorithm to estimate ZSD from OLI imagery using red and green band-ratio, leading to MAPE of 21.68% and RMSE of 0.076m for ZSD ranging from 0.1m to 1.05m. After satisfactory image-based validation, the algorithm was implemented on OLI data to derive ZSD patterns over ER and DTL from 2013 to 2017. Several crucial findings can be drawn: 1) Spatial-temporal patterns of ZSD exhibited notable fluctuations over both ER and DTL, and they also demonstrated a significant correlation with each other because of the opposite temporal cycle of ZSD fluctuations between ER and DTL; 2) Temporally, monthly fluctuations of ZSD between ER and DTL had opposite temporal cycles, which was mainly attributed to the surface runoff and sediment discharge driven by the outbound runoff variations of TGD. Spatially, the heterogeneity of the ZSD pattern in ER might have resulted from the different geographical regions being divided by large anthropologic hydrological facilities, such as TGD; 3) The relationship between ZSD and total suspended matter (TSM) showed a significant negative correlation, as did the relationship between ZSD and Kd(490). These findings demonstrate that TSM often plays a principal role in light attenuation of extremely turbid inland waters; 4) An inversed phenomenon of water clarity was observed at the intersection of DTL and the Yangtze River around Chenglingji site (YRAC), which was due to the opposite temporal cycle of ZSD fluctuations between DTL and ER after the impoundment of TGD; and 5) Owing to the analysis of noise-equivalent ZSD, OLI data can be used to derive ZSD, since the imagery uncertainty is 0.07m by means of our band-ratio algorithm, which demonstrates similar results to MODIS. The proposed ZSD-derived algorithm in this study could be suitable for other turbid lakes or reservoirs to formulate related strategies of water quality management in the middle and lower Yangtze River basin, and the unveiled findings here improve our understanding of ZSD spatiotemporal fluctuations in large river-connected lakes, such as Poyang Lake.

Quantifying the Effects of Near-Bed Concentration on the Sediment Flux after the Operation of the Three Gorges Dam, Yangtze River

The regime of sediment transport in the Jingjiang Reach has significantly changed from quasi-equilibrium to sub-saturation since the impoundment of the Three Gorges Dam (TGD), and vertical profiles of suspended sediment concentration (SSC) have changed accordingly. Vertical profiles of SSC data measured at three hydrological stations in the Jingjiang Reach (Zhicheng, Shaishi, and Jianli), before and after the impoundment of TGD, were collected and analyzed. Analytic results indicate a remarkably large concentration in the near-bed zone (within 10% of water depth from the river-bed) in a sub-saturated channel. The maximum measured concentration was up to 15 times the vertical average concentration, while the ratio in quasi-equilibrium channel was less than four times that. Concentrations normalized with reference concentration at the same height, and may decrease with increasing values of suspension index (settling velocity over shear velocity). In addition, concentration near the water surface may be larger than concentration in the near-bed region when the suspension index is smaller than 0.01. Sediment flux transported in the near-bed zone may be up to 35% of the total sediment flux in unsaturated flows. The relationship between deviations of estimating sediment flux when ignoring the near-bed concentration and discharge in flood season and non-flood season are different in unsaturated and quasi-equilibrium channels. Analysis indicates that, in the quasi-equilibrium channel, more attention should be paid to near-bed concentration during non-flood season, the same as measurements during flood season with larger discharge.

Wetland changes of China's largest freshwater lake and their linkage with the Three Gorges Dam

The impoundment of the Three Gorges Dam (TGD) has led to significant inundation shrinkage and water level decrease in China's largest freshwater lake, Poyang Lake. However, little is known about the influence on the lake's wetland landscapes. Here, using Moderate Resolution Imaging Spectroradiometer (MODIS) observations and a phenology-based decision tree approach, we present the spatial and temporal changes of the major wetland cover types from 2000 to 2014. Over the 15-year period, both total coverage of vegetation (Carex spp., Triarrhena lutarioriparia L. - Phragmites, sparse grass, and Zizania latifolia communities) and the area of each community (excluding floating aquatic macrophytes community or FAM) showed significantly increasing trends, with vegetation expanded towards the lake center. In contrast, the areas of water and mudflat have decreased significantly since the TGD impoundment, and they were mainly replaced by prominently expanded vegetated areas. The transition maps during 2000–2014 show that the vegetation community transitions occurred mainly from hydrophilic cover types to those adapted to dryer conditions. Despite the significant changes in wetland cover types, the most preferable water depth for each cover type remained stable before and after the TGD. In conclusion, the vegetation compositions are primarily controlled by water depth, indicating that the recent wetland changes can be directly linked to the TGD-induced hydrological regime-shift. These results provide a critical reference for local authorities to assess the potential influence of the newly proposed dam in this lake and to optimize its future operations with respect to modulating water levels.

Relationships Between Long-Term Trend of Satellite-Derived Chlorophyll-a and Hypoxia Off the Changjiang Estuary

The Changjiang Estuary is one of the largest estuaries in the world, where hypoxia frequently occurs during the summer season. Recent routine surveys in the observed area found that the low dissolved oxygen (DO) in the summer bottom water was not rapidly expanding with increasing nutrient loads in Changjiang diluted waters. Based on the remote sensing data and in situ data, we examined the historic seasonal hypoxia observations for the bottom waters of the Changjiang Estuary and investigated the short- and long-term effects that runoff had on variations in DO and chlorophyll-a (Chl-a). Our analysis indicated that the recent areal variation in hypoxia was due to the changing Chl-a distribution and stratification conditions. The correspondence between hypoxia and surface Chl-a concentration showed that remotely sensed Chl-a larger than 3.0 mg L−1 was an essential condition for the formation of hypoxia off the Changjiang Estuary. The trend of Chl-a concentration was significantly impacted by the Three Gorges Dam (TGD), and the inter-annual variation of Chl-a was weakly affected by global-scale climate variability. After the TGD impoundment, the sediment loading in the Changjiang runoff and suspended sediments in Changjiang Estuary in August decreased, and the high Chl-a concentration moved landward. These shifted the hypoxia from its optimal forming conditions.

Responses of landscape pattern of China’s two largest freshwater lakes to early dry season after the impoundment of Three-Gorges Dam

The effects of hydrologic cycle change (caused by human activity and global climate change) on ecosystems attract the increasing attention around the world. As a result of impounding of the Three Gorges Dam (TGD), climate change and sand mining, the dry season of Poyang Lake and Dongting Lake (China’s two largest freshwater lakes) came early after the TGD impoundment. It was the primary cause of the increasing need for sluice/dam construction to store water in the Lakes and attracted increasing attention. In this paper, we compared the landscape pattern between three hydrologic years with early dry season (EY) and three normal hydrologic years (NY) of each lake by remote sensing technology, to reveal the effect of early dry season on landscape pattern. The results showed that early dry season caused expanding of Phalaris to mudflat zone in Poyang Lake, while caused expanding of Carex to Phalaris zone and expanding of Phalaris to mudflat zone in Dongting Lake. In landscape level, there was no significant difference in landscape grain size, landscape grain shape, habitat connectivity and landscape diversity between EY and NY in the two lakes. While in habitat class level, there were significant changes in area of mudflat and Phalaris and grain size of mudflat in Poyang Lake, and in area of Carex, grain size of Phalaris and grain shape of Carex and Phalaris in Dongting Lake. These changes will impact migrating birds of East Asian and migratory fishes of Yangtze River.

Effect-Directed Analysis of Aryl Hydrocarbon Receptor Agonists in Sediments from the Three Gorges Reservoir, China.

The construction of the Three Gorges Dam (TGD) in the Yangtze River raises great concern in ecotoxicological research since large amounts of pollutants enter the Three Gorges Reservoir (TGR) water bodies after TGD impoundment. In this work, effect-directed analysis (EDA), combining effect assessment, fractionation procedure, and target and nontarget analyses, was used to characterize aryl hydrocarbon receptor (AhR) agonists in sediments of the TGR. Priority polycyclic aromatic hydrocarbons (PAHs) containing four to five aromatic rings were found to contribute significantly to the overall observed effects in the area of Chongqing. The relatively high potency fractions in the Kaixian area were characterized by PAHs and methylated derivatives thereof and heterocyclic polycyclic aromatic compounds (PACs) such as dinaphthofurans. Benzothiazole and derivatives were identified as possible AhR agonists in the Kaixian area based on nontarget liquid chromatography-high resolution mass spectrometry (LC-HRMS). To our knowledge, this study is the first one applying the EDA approach and identifying potential AhR agonists in TGR.

Three Gorges Dam alters the Changjiang (Yangtze) river water cycle in the dry seasons: Evidence from H-O isotopes

As the largest hydropower project in the world, the Three Gorges Dam (TGD) has attracted great concerns in terms of its impact on the Changjiang (Yangtze) River and coastal marine environments. In this study, we measured or collected the H-O isotopic data of river water, groundwater and precipitation in the mid-lower Changjiang catchment during the dry seasons of recent years. The aim was to investigate the changes of river water cycle in response to the impoundment of the TGD. Isotopic evidences suggested that the mid-lower Changjiang river water was ultimately derived from precipitation, but dominated by the mixing of different water masses with variable sources and isotopic signals as well. The isotopic parameter “deuterium excess” (d-excess) yielded large fluctuations along the mid-lower mainstream during the initial stage of the TGD impoundment, which was inherited from the upstream water with inhomogeneous isotopic signals. However, as the reservoir water level rising to the present stage, small variability of d-excess was observed along the mid-lower mainstream. This discrepancy could be explained that the TGD impoundment had significantly altered the water cycle downstream the dam, with the rising water level increasing the residence time and enhancing the mixing of reservoir water derived from upstream. This eventually resulted in the homogenization of reservoir water, and thus small fluctuations of d-excess downstream the dam after the quasi-normal stage (2008 to present). We infer that the retention effect of large reservoirs has greatly buffered the d-excess natural variability of water cycle in large river systems. Nevertheless, more research attention has to be paid to the damming effect on the water cycle in the river, estuarine and coastal areas, especially during the dry seasons.

Impacts of the Three Gorges Dam on the bathymetric evolution of the Yangtze River Estuary

The Three Gorges Dam (TGD) is the largest hydraulic engineering structure in the world. Its downstream impacts, especially on the Yangtze River Estuary, have attracted worldwide attention since its impoundment in 2003. A lack of high-accuracy bathymetric data that completely accounts for the Yangtze River Estuary makes it difficult to reliably document the influence of the TGD to any degree of detail. In this study, high quality bathymetric data, covering the Yangtze River Estuary from 2002 (pre-TGD) until 2013, were analyzed to delineate the bathymetric evolution of the Yangtze River Estuary during the post-TGD period and the effects of the TGD impoundment. After the completion of the TGD, deposition occurred in the Yangtze River Estuary in the inshore area from a depth of 6.4 m below the lowest tide, whereas there was significant erosion in the area below that water depth that intensified severely until 2013. In the area below the -19 m isobath, the bathymetry changed little, indicating a weak influence from the force of local water, so the -19 m water depth contour was proposed as a reference boundary for local bathymetric monitoring. The study area gradually changed from being deposition-dominated to being erosion-dominated between 2002 and 2007, and the erosion intensified with time after 2007. The amount of sediment eroded from 2002 to 2013 was more than 10×108 t. The trend in the local sediment flux from 2007 to 2011 relative to that in 2002 was correlated closely with the suspended sediment discharge from the TGD and the Datong gauging station, located 600 km from the Yangtze River Estuary, with a correlation coefficient greater than 0.99. This indicates that the TGD impoundment was the main mechanism that controlled the evolution of the Yangtze River Estuary after 2007. The intensified erosion in 2013 also in part reflects the insufficient sediment supply from the outer Yangtze River Estuary and the North Jiangsu coastal ocean.

Effects of hydrological regulation and anthropogenic pollutants on Dongting Lake in the Yangtze floodplain

AbstractDongting Lake, a wetland of international importance under the Ramsar Convention, is the hydrological lynchpin of the Yangtze floodplain. It is subjected to eutrophication and heavy metal pollution, but little is known of recent rapid degradation of its aquatic environment and potential causes. Here, we use sedimentary records of particle size, elements and pigments, combined with historical hydrological and limnological data, to assess aquatic environmental changes since ca 1960. Coarse particles in the sediments increased after 2003, while concentrations of K, Li, Al and Mg declined. These changes are probably linked to strong erosion of the downstream riverbed and declining supply of ion‐rich material from the upper Yangtze reaches after the Three Gorges Dam (TGD) began to operate. Furthermore, enrichment of sedimentary heavy metals and total phosphorus since the 1990s can be attributed to the influx of anthropogenic pollutants. Biotic responses are manifested in higher concentrations of fossil algal pigments, especially those from chlorophytes and siliceous algae after the TGD impoundment. Multivariate analysis revealed that changes in fossil pigments were significantly correlated with total phosphorus and Pb and three indicators for hydrological conditions (i.e. coarse particles, water exchange ratio and sediment discharge), indicating that influx of anthropogenic pollutants and hydrological regulation by the TGD are main drivers of algal community change. Our results provide reference conditions for restoration of Dongting Lake and highlight the importance of hydrological connection with the mainstream and pollution control for continuing efforts to restore Dongting Lake, as well as other similar floodplain lakes worldwide. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Impoundment Effects of the Three-Gorges-Dam on Flow Regimes in Two China’s Largest Freshwater Lakes

The impoundment of the Three-Gorges-Dam (TGD) significantly alters the flow regimes in Poyang and Dongting Lakes, the two largest freshwater lakes in China by reducing river discharge. This work aims to investigate the impoundment effects of the TGD on lake outflow and water level and clarify dynamic mechanism for the hydrological responses of both lakes to the TGD impoundment based on the typical case study. A hydrodynamic model is set up to simultaneously simulate hydrodynamics in the two lakes and the middle Yangtze River. Results show that TGD induces profound changes of the flow regimes in both lakes. The effects dynamically change with the TGD-induced Yangtze River discharge alteration, and are highly heterogeneous in space due to the complicated interactions between the lakes and the Yangtze River. The impoundment of the TGD accelerates Poyang Lake drainage. But that is not all for Dongting Lake, the TGD impoundment also reduces its water supply from the Yangtze River. The results from this work improve the understanding of the TGD impacts on the downstream river-lake system and provide scientific evidences for formulating better scheme for water resources management in this region.