Search Results (10)

Danjiangkou Reservoir is a world-famous large artificial freshwater lake that offers water resources for the middle route of the South-to-North Water Diversion Project in China. In this study, the distribution of carbon, nitrogen, and phosphorus in reservoir sediments and their pollution assessments were elucidated at different water periods. The average TN (total nitrogen), TP (total phosphorus), and TOM (total organic matter) contents were 794.8 mg/kg, 807.2 mg/kg, and 8.7% in the nonflood season, respectively. When the time comes to flood season, with the large amount of nitrogen pollution inputted from peripheral nonpoint sources and phosphorus released by the accelerated exchange of water bodies, the average TN concentration increased to 1061.2 mg/kg. In addition, the average TP and TOM contents were reduced to 559.5 mg/kg and 6.3%. Nutrient pollution fluctuated between the safe and lowest level. Reservoir eutrophication risk was low. There was a certain nitrogen enrichment in the Danjiangkou Reservoir, and the flood season was the main period of nitrogen pollution input. Water exchange during flood season might accelerate organic matter degradation. Near the dam, sediment organic matter content increased significantly, reaching severe pollution levels. The results of the simulated sediment nutrient release test showed that the nitrogen and phosphorus in the reservoir would release slowly. Moreover, their annual release flux was calculated as 470.4 t and 87.9 t, respectively. It illustrated that the internal pollution of Danjiangkou Reservoir was light, and the release amount was small, so it was not the main pollution source of the reservoir at present. Full article

Reservoir water and rainfall are the two main factors affecting the seepage of earth-rock dams, but the seepage measurement includes the seepage discharge caused by the reservoir water and rainfall. Only by obtaining the seepage discharge caused by the reservoir water can we evaluate the seepage safety state. In this paper, a statistical model for seepage monitoring of earth-rock dams is established. Normal distribution function and Rayleigh distribution function are used as the lag functions of reservoir water and rainfall, respectively. The grey wolf algorithm is used to solve the lag days, and the partial least square method is adopted to solve the regression coefficient of the statistical model. Then, the reservoir water (main water) and rainfall infiltration (foreign water) parts of the measuring weir are separated with the statistical model. The developed method is used to separate the main and foreign water parts of the three measuring weirs of the Danjiangkou earth-rock dam. The results show that the overall accuracy of the models is high (the multi-correlation coefficients are about 0.95), and the separated main and foreign water seepage discharge conforms to the seepage law of earth-rock dam, which verifies the effectiveness of the method. Full article

Danjiangkou Reservoir is the water source of the mid-route of the South-to-North Water Transfer Project. The source, distribution and potential risk of antimony in its water and sediments are rarely reported. In this study, symmetrical investigation results demonstrated that the concentration of antimony in the Han sub-reservoir and water in front of the dam fluctuated at about 0.9 mg L⁻¹, while it was relatively higher and increased with the distance from the dam in Dan sub-reservoir water, with an annual average of 0.93~3.15 mg L⁻¹. In recent years, the concentration of antimony in the Danjiangkou Reservoir showed a downward trend, and the difference between the Han and Dan sub-reservoirs decreased significantly. The antimony in the sediments in the reservoir was primarily derived from the inflowing rivers, and it was higher in the Dan sub-reservoir than in the Han sub-reservoir. The concentration of antimony in the water in the reservoir was considerably higher than the background value in the watersheds, indicating that there is an external input with decreasing input intensity. The content of antimony in the sediments in the reservoir and its inflow rivers was substantially higher than the background value of watersheds, indicating that there is a certain degree of enrichment. In addition, the antimony mining industry in the water source area poses a risk to the water safety of the reservoir. Antimony is not a conventional pollutant. Consequently, the collection of antimony monitoring results is a challenging task. Additionally, this study fills the gap in regional antimony research. Furthermore, the ecological risk assessment of antimony in China is still in its infancy. Unquestionably, the study of the temporal and spatial distribution of antimony concentration will be beneficial for the protection of water sources in relevant regions. Full article

The Danjiangkou hydropower station is a water source project for the middle line of the South-to-North Water Transfer Project in China. The dam is composed of riverbed concrete dam and earth rock dam on both banks, with a total length of 3442 m. Once the dam is wrecked, it will yield disastrous consequences. Therefore, it is very important to evaluate the dam safety behavior in time. Based on the long-term and short-term memory (LSTM) network, the deformation prediction models of the embankment dam of the Danjiangkou hydropower station are constructed. The models contain two LSTM layers, adopt the rectified linear unit function as the activation function and determine the super parameters of the models with Bayesian optimization algorithm. According to the settlement monitoring data of LD12ZT01 measuring point (dam crest 0 + 648) on the left bank of the embankment dam of the Danjiangkou hydropower station from July 2013 to March 2022, the LSTM and bidirectional LSTM models are constructed. In total, 80% of the monitoring data are taken as the training set data and 20% of the monitoring data are taken as the test set data. The mean absolute error, root mean square error and mean square error for the test set are 0.42978, 0.56456 and 0.31873 for partial least squares regression (PLSR), 0.35264, 0.47561 and 0.22621 for LSTM and 0.34418, 0.45400 and 0.20612 for bidirectional LSTM, respectively. The results show that the bidirectional LSTM model can obtain better deformation prediction value than the LSTM model and the PLSR. Then, the bidirectional LSTM model is used to predict the settlement value of LD16YT01 measuring point (dam crest 0 + 658) on the right bank, and the mean absolute error, root mean square error and mean square error for the test set are 0.5425, 0.66971 and 0.4520, respectively. This shows the bidirectional LSTM model can effectively predict the settlement value of the embankment dam of the Danjiangkou hydropower station. Full article

The Danjiangkou Reservoir in China is characterized by significantly high concentrations of total nitrogen (TN), and the sources are not clear. Recently, research on this reservoir has focused on the N cycle, the spatial and temporal distribution characteristics of N, and the factors influencing N concentration. Significant temporal and spatial differences in TN concentrations exist, both in the reservoir area and the tributaries. N concentration in the area is affected by numerous factors, including N transported by tributaries, nonpoint source pollution around the reservoir, internal N release, and atmospheric N deposition. Moreover, a dam heightening project led to a larger water-fluctuation zone and more bays in the reservoir, directly affecting its N cycle. However, further research is required to explore the N cycle on a large watershed scale in the Danjiangkou Reservoir and upper stream areas, determine N pollution sources using satellite remote sensing, and conduct simulations of a water body N cycle model based on data fusion. Although the issue of excessive TN has been alleviated to some extent by the South-North Water Diversion Project, the excessively high TN concentrations require more research to aid the implementation of N-reducing strategies. Full article

Large reservoir projects typically occupy vast lots of rural land and trigger resettlement on a massive scale. In China’s reservoir context, increasing concerns have arisen regarding distant-resettlees (those who are resettled outside the reservoir area), while fewer studies have examined the nearby-resettlees (those who are resettled near the original area) and the non-movers (those who do not resettle). The significance of these two groups has been downplayed and their populations are in the millions (or more) in China. How and why they are impacted is under-researched and their relative position and intergroup nexus with the distant-resettlees remains unclear in the existing literature. To address this research gap, this paper incorporates the differences between nearby-resettlees and non-movers and collectively refers to them as the “stayers” as they are left behind in reservoir areas. Based on the background of reservoir-induced resettlement in present-day China, and a review of the project-induced impacts, we use Danjiangkou Reservoir as a case study. The findings indicate that the stayers are largely disadvantaged in terms of land assets, housing conditions, finance, infrastructure, industrialisation, livelihood strategies, and emotional impact, while many distant-resettlees are less affected or positively impacted in these aspects. Through the lens of the political nature of reservoir-induced resettlements, we interpret the gaps between the distant-resettlees and stayers. Finally, domestic and global policy implications and further comments are presented. Full article

Knowledge of river engineering impacts on water discharge is significant to flow guidelines and sustainable water resource managements for balancing human consumption and the natural environment. In this study, based on the collected multi-decadal discharge data at Yichang, Hankou, and Datong stations, we determined that in October, Three Gorges Dam contributed 34.4%, 24.5%, and 18.7% to the discharge decrease in the upper, middle, and lower reach, respectively, while Gezhouba Dam contributed 14.5%, 10.7%, and 10%. Danjiangkou Reservoir caused the discharge ratio of Hanjiang to Changjiang to decline from 7.2% during 1954–1973 to 6.3% during 1973–2014. Owing to growing water withdrawal and consumption, we suggest that the distribution of water diversion and consumption should be regulated to prevent the probable occurrence of the severe issue of salt water intrusion in the Changjiang Estuary in 2028. Full article

A large number of water resources development projects have significantly changed the natural flow regime of the middle and lower reaches of the Hanjiang River, especially the Danjiangkou Reservoir, cascade reservoirs, the South-to-North Water Diversion Middle Line Project and their compensation projects, completed in 1973, 2000, and 2014, respectively. The daily streamflow data of three stations in the middle and lower mainstream of the Hanjiang River are divided into four periods corresponding to pre-impact (1954–1973), interim (1974–1999), transition (2000–2013) and post-impact (2014–2018). Eco-flow metrics and indicators of hydrologic alteration (IHA) were used to study the change of natural flow regime. The annual streamflow decreased gradually during the four periods. The construction of the Danjiangkou Reservoir increased streamflow, minimum flow value, and the number of reversals in the dry season along the middle and lower course of the Hanjiang River. Moreover, the dam reduced streamflow, maximum flow value, low pulse duration, and the rise and fall rates in the wet season. Additionally, the streamflow reduced corresponding to the completion of cascade reservoirs and the Middle Route of South-to-North Water Diversion Project. In particular, the streamflow decreased drastically from July to September, affected by the Middle Route of the South-to-North Water Diversion Project. Furthermore, the compensation projects, such as the Yangtze-Hanjiang Water Diversion Project, mitigate the reduction of streamflow from July to September in the downstream. The study provides insights into the ecological and economic benefits associated with water resources development and use in the mainstream of the middle and lower course of the Hanjiang River for the achievement of sustainable development in the region. Full article

Channel bars are essential landforms and their evolution is crucial to aquatic and riparian biodiversity, river’s water-sediment process, and economic development. With the development of water conservation facilities and hydropower projects, numerous changes have been taken place in hydrological regimes and morphology. There have been many changes on channel bars in the middle reaches of Hanjiang River due to the combined effects of cascade reservoirs. However, little was known about such dynamics and their linkages to cascade dams across the entire downstream area. Using Landsat remote sensing images from 1986–2018 and the threshold binary Otsu extraction method, this study completed comprehensive monitoring of nine mid-channel bars (DX1–DX7, XZ1, and XZ2), and three shoal group (XZ3–XZ5) dynamics. Results showed that the mid-channel bars’ area in the reach from Danjiangkou to Xiangyang (DX) decreased over the past 33 years, with the exception of DX4, while the total area decreased by 23.19%, this channel bars’ area change was mainly influenced by backwater from the Cuijiaying Reservoir with high water level after 2010 (r = −0.93, p < 0.01). The total channel bar area from Xiangyang to Huangzhuang (XZ) decreased by 16.63% from 1986 to 2018. The total channel bar area in XZ had a strong negative correlation with runoff at Huangzhuang hydrologic station (r = −0.79, p < 0.05), which was partly attributed to upstream precipitation according to the high correlation between runoff and precipitation (R² = 0.65). In general, the DX section was under equilibrium between scouring and deposition compared to downstream Xiangyang, the bars in DX section were mainly affected by water level, and bars in XZ section during 1986–2018 were complicated because it was upstream eroded and downstream deposited. In addition, vegetation cover, revetments, flood events, sand mining, land use, and over-exploitation may cause channel bar area dynamics. Hence, more continuous investigations are suggested to focus on effects of cascade reservoir operation on hydrological regime, as well as the changing morphology of channel bars in the middle reaches of the Hanjiang River. Full article

Drinking water safety is increasingly perceived as one of the top global environmental issues. Plankton has been commonly used as a bioindicator for water quality in lakes and reservoirs. Recently, DNA sequencing technology has been applied to bioassessment. In this study, we compared the effectiveness of the 16S and 18S rRNA high throughput sequencing method (HTS) and the traditional optical microscopy method (TOM) in the bioassessment of drinking water quality. Five stations reflecting different habitats and hydrological conditions in Danjiangkou Reservoir, one of the largest drinking water reservoirs in Asia, were sampled May 2016. Non-metric multi-dimensional scaling (NMDS) analysis showed that plankton assemblages varied among the stations and the spatial patterns revealed by the two methods were consistent. The correlation between TOM and HTS in a symmetric Procrustes analysis was 0.61, revealing overall good concordance between the two methods. Procrustes analysis also showed that site-specific differences between the two methods varied among the stations. Station Heijizui (H), a site heavily influenced by two tributaries, had the largest difference while station Qushou (Q), a confluence site close to the outlet dam, had the smallest difference between the two methods. Our results show that DNA sequencing has the potential to provide consistent identification of taxa, and reliable bioassessment in a long-term biomonitoring and assessment program for drinking water reservoirs. Full article