Gorges Reservoir Operation Research Articles

Runoff variation in the middle and lower branches of Yangtze River and the two lakes (Dongting and Poyang Lake) before and after Three Gorges Reservoir's operation

为探索三峡水库运行前后长江中下游干流及两湖径流过程的变化及其驱动因素,利用宜昌、监利、大通、七里山、湖口共5个水文站的流量资料,分析了各站径流过程的变化特征及其成因。结论:(1)各站年径流量均减少,但除七里山站之外,其它各站减少比例均小于10%且变化不显著;(2)干流各站月径流量最大减幅发生在10月,而七里山站、湖口站分别发生在7月、4月;(3)干流各站月径流量最大增幅发生在3月,而七里山站、湖口站分别发生在1月、6月;(4)宜昌站,1-4月径流量增加是三峡水库入库径流增加和水库调度的共同作用结果,6-8月径流量减少的主因是三峡水库入库径流量减少,5、9、10月径流量变化的主因是三峡水库调度;(5)监利站,径流量的变化与宜昌站表现出高度的一致性,但冬季各月径流量的增幅均大于宜昌站;(6)大通站,4-6月径流量变化方向与湖口站一致,其它月份变化方向均与宜昌站一致。(7)七里山站,7月径流量减少的主因是洞庭湖流域来水减少,9、10月径流量减少的主要原因是荆江分流减少,但洞庭湖流域来水减少也是重要原因。(8)湖口站,4、5月径流量减少的主因是流域降水减少,9、10月径流量减少的主要原因是鄱阳湖汛期水位降低、低水位提前、蓄水量减少。;To explore and explain the changes of runoff process in the middle and lower Yangtze River mainstream and the two lakes of Dongting and Poyang before and after the operation of the Three Gorges Reservoir (TGR), the runoff data of five hydrological stations, which are Yichang, Jianli, Datong, Qilishan, and Hukou, were used. The stations of Yichang, Jianli, and Datong locate along the mainstream of the Yangtze River, while the other two stations locate at the exit of the Dongting and Poyang Lake, respectively. The runoff changes at each station before and after the TGR's operation and its causes were analyzed. Conclusions include: (1) The annual runoff at each station decreased, except at Qilishan Station, the reduction ratio of runoff at other stations was less than 10% and their changes were not significant; (2) The maximum decrease in monthly runoff at each mainstream station occurred in October, except that at Qilishan Station and Hukou Station it occurred in July and April, respectively; (3) The maximum increase in monthly runoff at each mainstream station occurred in March, while at Qilishan Station and Hukou Station it occurred in January and June, respectively; (4) At Yichang Station, the increase of monthly runoff from January to April resulted from both the inflow increment of the TGR and its operation. The main reason for the decrease in monthly runoff from June to August was the decrease in the inflow of the TGR. The main reason for the runoff change in May, September and October was the operation of the TGR; (5) At Jianli Station, the change of runoff was highly consistent with that at Yichang Station, but the increase of runoff at Jianli Station in each month in winter was greater than that at Yichang Station; (6) At Datong Station, from April to June the change direction of monthly runoff was the same as that at Hukou Station, and the change direction of other months was the same as that at Yichang Station. (7) At Qilishan Station, the main reason for the runoff reductions in July was the reduction of rainfall in Lake Dongting basin, and while the reduction of the diversion from Jingjiang River is the main cause to the runoff reduction in September and October, the reduction of rainfall in Lake Dongting basin also played an important role; (8) At Hukou Station, the decreases in runoff in April and May resulted from the reduction of rainfall in Lake Poyang basin, while the main reason for the runoff decreases in September and October was the reduction of water level in Lake Poyang during the previous months, which led to the early low water level season and the reduction of water storage.

Ecological risk assessment on the habitats of typical aquatic species in the middle reach of the Yangtze River: Implication for three gorges reservoir operation

The operation of a reservoir may change natural hydrological processes, thus affecting the habitat of aquatic organisms. However, the risks posed by reservoirs on aquatic organisms remain to be fully evaluated. In this study, a risk assessment model was established to assess the ecological risk of reservoir flow regulation based on the consequences of deviating from the environmental flow range of an aquatic habitat. We applied this model to the Three Gorges Reservoir by obtaining the risk time series of different aquatic habitats in the Yangtze River before and after the construction of the reservoir. The risk analysis results showed that when habitat discharge is above or below the appropriate range of environmental flows, the ecological risk increases. The Chinese sturgeon, four major Chinese carp species, and finless porpoise habitats were identified to be at low-flow risk, low-flow risk, and high-flow risk, respectively. We suggest that the habitat flows of Chinese sturgeon, four major Chinese carp species, and finless porpoise during the spawning period should not be less than 6,850, 7,000, and 13,500 m3/s, respectively. The results of this study could help river managers optimize reservoir operations to minimize risks and maximize ecological benefits.

Effects of the Three Gorges Reservoir Operation on Vertical Distribution of Chlorophyll a and Environmental Factors in Tributaries

The hydrodynamics and environmental factors in the Xiangxi River (XXR) and Shennong River (SNR), which are tributaries of the Three Gorges Reservoir (TGR), were monitored from July to August (the low water level period) and in October (the impoundment period) in 2018. The vertical distribution characteristics of chlorophyll a and other indicators of the two tributaries were analyzed during the different operation periods, and the factors that affected the vertical distribution in each period were discussed. The results showed that the vertical distribution of dissolved oxygen, water temperature, pH value, and chlorophyll a of the XXR and SNR during the low water level period was relatively consistent. The indexes 0-10 m (0-5 m for chlorophyll a) from the surface of the XXR and SNR, respectively, showed significant stratification and decreased with increasing water depth; the stability index of thermal stratification (RWCS/H) was 13.71-29.07 m-1, which was stable. After the water depth reached 10 m (5 m for chlorophyll a), the indexes tended to be stable along the water depth. During the impoundment period, there was no obvious stratification for each index; the stability index of thermal stratification was 0-0.5 m-1, the stability of the water body was weak, and the vertical variation of each index was relatively stable. The comprehensive trophic state index (TLI) of the XXR and SNR were 55 and 53 during the low water level period, respectively, indicating that they were in a slightly eutrophic state, and 39 and 46 during the impoundment period, respectively, indicating a mesotrophic state. Linear regression analysis showed that chlorophyll a, dissolved oxygen, water temperature, and pH in the two tributaries were significantly correlated in the vertical direction in the low water level period, indicating that dissolved oxygen, water temperature stratification, and pH were important factors affecting the vertical distribution of chlorophyll a. During the impoundment period, a large amount of backflow from the Yangtze River, a large fluctuation in tributary water level, and the decrease in RWCS/H were the important factors that affected the small vertical change in the water body. The enhancement of vertical mixing and the decrease in Zeu/Zmix were the key factors affecting the nutritional status of the water.

Multi-objective game theory optimization for balancing economic, social and ecological benefits in the Three Gorges Reservoir operation

Reservoir operation is an important and effective measure for realizing optimal allocation of water resources. It can effectively alleviate regional scarcity of water resources, flood disasters and other social problems, and plays an important role in supporting sustainable strategic development of water resources. Coordinating the stakeholders is key to the smooth operation of a multifunctional reservoir. This research examines the competition among stakeholders of a multi-objective ecological reservoir operation aiming to provide for economic, social and ecological demands. A multi-objective game theory model (MOGM) specified 10-day water discharge to meet the triple water demands (power generation, socio-economic consumption and environment) for multi-purpose reservoir operation. The optimal operation of the Three Gorges Reservoir (TGR), with the ecological objective of providing comprehensive ecological flow demanded for some key ecological problems that may occur in the middle and lower reaches of the Yangtze River, was chosen as a case study. Discharged water calculated by the MOGM and a conventional multi-objective evolutionary algorithm/decomposition with a differential evolution operator was then allocated to different demands. The results illustrate the applicability and efficiency of the MOGM in balancing transboundary water conflicts in multi-objective reservoir operation that can provide guidance for the operation of the TGR.

Analysis on variation characteristics of the minimum flow at Datong Station under the influence of the Three Gorges Reservoir

As an important hydrological control station in the lower reaches of the Yangtze River, the Datong Station can provide guidance for regulating downstream water withdrawal activities by studying the characteristics of its changes during the dry season. This study selected the annual minimum flow index, applied linear trend method, Mann-Kendall method and wavelet analysis method to analyze its trend and periodic change characteristics, and analyzed the empirical frequency changes before and after the operation of the Three Gorges Reservoir, and obtained the following conclusions: The annual minimum flow series shows a significant increase trend, showing the characteristics of multi-period nesting in periodic changes, in which the first main period is 35-year. At the same frequency, the corresponding flow after the Three Gorges Reservoir operation was all larger than that before.

Analysis of critical river discharge for saltwater intrusion control in the upper South Branch of the Yangtze River Estuary

Saltwater intrusion in the estuary area threatens the use of freshwater resources. If river discharge increases to a critical value, then saltwater intrusion frequency and salinity level decreases. In this study, long-term river discharge and tidal range data in the Yangtze River Estuary (YRE) and salinity data obtained in the upper South Branch of the YRE were used to analyze the characteristics of different variables and the basic law of their interactions. Two methods, namely, the material analysis method and empirical models, were applied to determine the critical river discharge for saltwater intrusion control. Results are as follows: (1) the salinity might exceed the drinking water standard of China when the river discharge was less than 30,000 m3/s. Approximately 69% of salinity excessive days occurred when the river discharge was less than 15,000 m3/s; (2) the tidal range in the YRE roughly varied in sinusoidal pattern with a 15-day cycle length. Exponential relationship existed between daily salinity (chlorinity) and daily mean tidal range. Combining these two features with the cumulative frequency statistics of tidal ranges, it was showed that notable saltwater intrusion occurred when the tidal range was more than 2.7 m at Qinglonggang station. Moreover, the critical discharge was found to be slightly higher than 11,000 m3/s; (3) various of empirical models for salinity prediction could be chosen to calculate the critical discharge. The values obtained by different models were in the range of 11,000-12,000 m3/s; (4) the proposed critical discharge to reduce notable saltwater intrusion was 11,500 m3/s. After the Three Gorges Reservoir operation, the minimum river discharge into the YRE in 2008–2017 was below the critical discharge, thereby suggesting an increase in the minimum river discharge by reservoir regulation in drought periods.

Disintegration law of strongly weathered purple mudstone on the surface of the drawdown area under conditions of Three Gorges Reservoir operation

Mudstones locating on surfaces of drawdown area of a bank slope in Three Gorges Reservoir (TGR) are prone to disintegrate under cyclic wetting-drying (WD) conditions during the reservoir operation, which will have adverse effects on the slope stability. In order to study disintegration law of the mudstones, 9 strongly weathered purple mudstone (SWPM) samples from the Middle Triassic Badong group (T2b) in TGR area were collected to conduct laboratory-based cyclic WD experiments under ambient stresses (0.0 MPa, 0.5 MPa and 1.0 MPa) using a novel self-developed experimental system. Meanwhile, grain size distribution curves of materials slaking form the mudstone samples were measured after each WD cycle. Grain size distribution curves and disintegration phenomena of the SWPM samples show that disintegration degree decreases with the increase of ambient stresses when the mudstone undergoes the same wetting-drying cycles, and it increases with the increase of wetting-drying cycles under the same ambient stress. A new index, disintegration coefficient (Dt), is proposed to describe the disintegration degrees of the mudstone under conditions of reservoir operation (WD cycles and ambient stresses). The changes of disintegration coefficient suggest that the SWPM on the surface of the drawdown area is more likely to disintegrate under smaller ambient stress in the course of reservoir operation.

Impact of the three gorges reservoir operation on the hydrological situation of Poyang Lake

The operation of Three Gorges Reservoir (TGR) has changed the hydrological situation of Yangtze River and its connected lakes. Based on the hydrodynamic model, the influence of TGR operation from 2009 to 2014 on the Poyang Lake has been evaluated. It is found that TGR impoundment reduced the discharge of the Yangtze River and the water level of Poyang Lake, brought the decreasing of the backflow phenomenon. Especially in October, the discharge and water level of Hukou station (HKS) decreased by 9.6% and 1.09 m respectively, and this effect could be up to the Kangshan area. Meanwhile, TGR operation has also increased the water level of HKS by 0.1~0.56 m from December to May, which only affected the vicinity of Duchang. In addition, TGR operation also increased the maximum water level of HKS from April to June by 0.1~0.34 m, and that from July to August decreased by 0.22~0.4 m which is beneficial to reducing the flood control risk of Poyang Lake. But TGR impoundment changed the water exchange process between Yangtze River and Poyang Lake, and advanced the dry season, which had a certain impact on the water supply and ecological environment of the lake area.

Back Analysis of a Recent Progressive Failure in China Three Gorges Reservoir Area: Shanshucao Landslide

Abstract The Shanshucao landslide is a recent landslide that occurred in the China Three Gorges Reservoir area. It is next to the Daling Hydropower Station landslide, one of the geological hazard professional monitoring points in the China Three Gorges Reservoir. The Shanshucao landslide had not shown a significant deformation during recent decades until September 2nd, 2014. On that day, the Shanshucao landslide abruptly started to move at around 9 a.m. local time, stopped at 13:19 p.m., and caused a 43.2 × 104m3 landslide mass which slipped into the Luogudong River, the secondary branch of Yangtze River. Fortunately, the local government gave an efficient early warning and organized a successful emergency evacuation. Nobody was injured or killed in this landslide failure event. The Daling Hydropower Station and its attached buildings were eradicated by the landslide. Posterior to the failure, a newborn free surface occurred on the dip slope. The remaining body of the landslide poses a great threat to the safety of both the village and the Three Gorges Reservoir operation. Subsequently, an emergency monitoring system has been placed on the slope to observe any subsequent deformation. By applying the kinematic model, this article will give a general outlook on the failure event and investigate the geological features which caused the slope instability. Also, the two inclined blocks models are introduced in the back analysis and show a good comparison to the site observation results. This article will provide guidance and suggestion for the stability analysis of similar highly weathered bedded landslides in the China Three Gorges Reservoir area.

The influence of Three Gorges Reservoir high water level on the rainfall runoff

After Three Gorges Reservoir building up, the natural river course and the near hillside inside the backwater region are inundated to form a fairly wide man-made lake which affects the hydrological characteristics and floodwater transmission to different degrees. When the reservoir impound to high water level, the conflux time is obviously shortened, the flood-peak discharge increase, and the peak type became sharper. The change of runoff yield and concentration makes the forecast scheme unable to be applied well. Based on the practice of Three Gorges Reservoir operation, the rainfall-runoff characteristics of the backwater region under the condition of high water level are analysed and summarized, then a set of unit hydrographs suitable for rainfall-runoff calculation are recalibrated, which has great reference value for hydrological forecasting of Three Gorges region.

Effects of river-lake interactions in water and sediment on phosphorus in Dongting Lake, China.

As a large river connected lake, Dongting Lake is influenced by anthropogenic activities and the discharge from its upstream tributaries in the lake basin and by the water recharge via a connection to the Yangtze River (YR) outside the basin. This makes the lake phosphorous cycle more complex than that in other disconnected lakes. Here, we calculated section fluxes and ran a hydrodynamic model to investigate the phosphorus (P) variations in response to the changing interactions in the water and sediment between the YR, four tributaries, and the lake. Results show that particulate P was the dominant form with a significant linear relationship with suspended sediment (r 2=0.906). The sediment input reduction from the YR through three water inlets, which is closely related to the Three Gorges Reservoir operation since 2003, led to a decrease in the total P (TP) concentration in the western Dongting Lake. However, the impact and range of this decrease were fairly limited. Compared with the limited effect of the YR, the raised TP flux from the Yuanjiang tributary controlled the TP concentration at the outlet of the western Dongting Lake. Apart from the influence of the YR and the tributaries, anthropogenic activities (sand dredging) in the eastern Dongting Lake also contributed to a high TP concentration around the S10 area through sediment resuspension. We suggest that, compared with the reduction in TP flux and sediment load from the connected Yangtze River outside the basin, the elements within the basin (increased TP input from tributaries and sand dredging) have a greater effect on the variations of TP in Dongting Lake.

Spatiotemporal response of pelagic fish aggregations in their spawning grounds of middle Yangtze to the flood process optimized by the Three Gorges Reservoir operation

Flood patterns altered by regulation and operation of the Three Gorges Reservoir (TGR) on the Yangtze has negatively affected fish spawning downstream, particularly results in the decline of spawning sizes. The TGR release was optimized by reoperation for enhancing fish reproduction downstream since 2011. Response of spawning sizes to the flood alteration was documented, yet litter is known concerning the adult fish. Accurate estimate of spatiotemporal changes and abundance of adults in the spawning grounds is critical for quantifying the contribution of flood changes to the spawning. This study used hydroacoustic surveys to document the response of fish aggregations to the changes of flood process (i.e., deployed before-, during- and after flood) on the Jingjiang- and Yichang spawning ground. Acoustic signals from fish tracking were allocated into two groups according to frequency distributions of Target strength (TS), defined as small fish (−60 dB < TS < −35 dB) and large fish (TS > −35 dB). Sizes of small fish acquired before- and during flood were significant larger than those acquired after flood whereas no significant different observed for large fish. Both small and large fish aggregated in both spawning grounds during flood and disappeared after flood. Besides, fish numbers presence in both spawning grounds during flood was greater than those before and after flood. This study suggested spatial distributions of fish aggregations with different sizes in both spawning grounds shifted with the flood changes. Fish aggregated into the spawning grounds for spawning during the flood and departed after the flood, resulting in large fish numbers presence during the flood period. Further research is required to reveal relationships between the hydrological and hydraulic changes results from flow alteration and fish responses to realize their precise requirements and behaviors for spawning.

Eco-hydrological impacts of Three Gorges Reservoir's operation on three outfalls of Chingjiang River

Based on the measured daily flow prototype sequence of five hydrologic stations in the three outfalls of Chingjiang River from 1990 to 2014, its hydrological characteristics and its changing trend was analyzed by using the Mann-Kendall statistical test and the cumulative anomaly method, while the effect of the operation of the Three Gorges on the variation of the 33 indexes of ecological hydrology was also analyzed by the index system of ecological hydrology and range of variability approach. The results showed an obvious decreasing trend in annual mean discharge with the confidence degree of 95% with a decrease rate of 19% during 1990-2014. The jump point appeared in 2003, with the annual mean discharge being 1981.1 m3·s-1 before 2003 but 1603.25 m3·s-1 after. There was an obvious increase in monthly mean discharge from January to April (the degree of deviation was 1.58, 1.86, 0.83 and 0.62 respectively), an obvious increase in the late May and the early June, a slight decrease in July and August (the degree of deviation was -0.12 and -0.10 respectively), and a significant decrease in October (the degree of deviation was -0.40). There was a great change in annual minimum flows while a slight change in most of the annual maximum flows and a moderate decrease in 1-day and 3-day maximum flow. It also had a great change in duration and frequency of the low-flow pulse and slight change in high-flow pulse.

Spawning activity of the four major Chinese carps in the middle mainstream of the Yangtze River, during the Three Gorges Reservoir operation period, China

Summary River flow alterations caused by dams have introduced many ecological problems, in particular a decline in aquatic species such as fishes. One compensatory measure is to create a hydrological process similar to the natural state with regard to the survival requirements of the fish. In recent years, the Three Gorges Reservoir (TGR) has introduced man-made flood by ecological operation experiments to facilitate spawning of the four major Chinese carps in the Yangtze River, China. To investigate the fish spawning activities and their responses to the TGR operation, eggs from the four major Chinese carps were sampled using conical drift nets in the middle mainstream of the Yangtze River, May to July in 2012 and 2013. Spawning timing, location, and scale of the four carps were studied and compared between the 2 years; key hydrological and environmental factors associated with spawning were determined by principal component analysis and stepwise regression analysis. Two factors were significantly positive when correlated with egg abundance: one was increasing rate of the river flow (flood amplitude), and the other was river transparency; only one factor, starting of the river flow (flooding occasions), was significantly and negatively correlated with the time of spawning. Comparison of egg abundance in one flood pulse response to different operation rules showed that flooding made by an ecological operation induced a larger scale of spawning than a conventional operation. The study implied that suitable flood conditions could produce a successful spawning event, and that the occasion and pattern of the flood process might result in different responses in fish spawning. Further research is required to develop more scientific monitoring designs in order to obtain accurate field data for both biotic and abiotic factors, and explore new research methods for egg abundance estimations combined with particle experiment and hydrodynamic modeling. This work is fundamental to improve the strategic decisions on reservoir operation and river management.

三峡水库运行期间原生动物群落时空异质性研究

三峡水库运行期间原生动物群落时空异质性研究

Analysis of the Three Gorges Reservoir Operation on the Water Level of Yangtze River during the Non-Flood Season

In the middle and downstream area of the Yangtze River, low water levels had occurred at post-flood season or before the flood season in recent years, since the trial impoundment of the Three Gorges Reservoir (TGR) in 2008. Based on the analysis of the low water levels, both rating curve of main stations in the middle and lower reaches of the Yangtze River and the operation of TGR in the dry season were analyzed in study to reveal the effects of the impoundment of TGR on water level of downstream areas. The research results show that the water supplement of the TGR could raise the downstream water level, which has positive effect on water supplement and navigation in this area.

Stability of Huangtupo I# Landslide under Three Gorges Reservoir Operation

Abstract. During the normal operation of Three Gorges Reservoir, the water level of the reservoir will fluctuate periodically, which will soften and decrease the shear strength of rock soil on the bank, meanwhile decrease the landslide stability. Huangtupo landslide is a typical large and complex landslide in the Three Gorges Reservoir Region, which is consist of four sub-landslides. In particular, the stability of its riverside Huangtupo I# landslide has a great stake. Based on the analysis of engineering geological condition of Huangtupo landslide, the 2D finite element model of Huangtupo I# landslide(The Riverside Slumping mass I#) was established, the proper mechanical parameters was selected. By using the GeoStudio software, according to the reservoir running curve, the simulation on coupling effect of seepage field and stress field was conducted in 7 different modes within the period of one year. The results showed that: ①the reservoir water level fluctuations will affect both the displacement in saturated and un-saturated area of landslide; especially when the water level drawing down sharply; ②the stability coefficient of Huangtupo I# changes with the reservoir water level fluctuations; the minimum stability coefficient occurs 48 days after the water level drawing down and the moment when the water level falls by 11.9m, under that moment the Huangtupo I# is unstable.

Impact of the Three Gorges reservoir operation on downstream ecological water requirements

With population increase and economic growth, the flow regime of the Yangtze River has been altered to some extent by human activities, particularly dam construction. Dam-induced alterations in the flow regime of the Yangtze River will unavoidably influence water allocation among different water users and instream ecological water requirements may not be guaranteed during some months, particularly during phases of reservoir storing water. To assess the impacts of the Three Gorges reservoir operation on the downstream minimum instream ecological water requirements, this paper selected the Three Gorges reservoir and Yichang hydrological station below the reservoir as case study sites. On the basis of long-term time series of daily discharge data, the reservoir outflow was simulated under two water storing schemes and the degree to which the downstream minimum ecological flow was satisfied was computed. The results of this paper could provide references for the integrated management of the Yangtze River water resources and the assessment of dam-induced impacts on the Yangtze River ecosystem health.

Impact analysis of the Three-Gorges Project on the spawning of Chinese sturgeon Acipenser sinensis

Summary The spawning run of adult Acipenser sinensis was blocked by the Gezhouba Dam in 1982 and the flow line was altered again in October and November, when during the spawning period the Three Gorges Project (TGP) started to fill the reservoir with water. This alteration of river flow may affect spawning of A. sinensis. By comparing historical river flow records at spawning dates and outflow at the design year from TGP, we found that A. sinensis spawning in the Yangtze river took mostly place below the Gezhouba Dam on the flood receding period, and discharge volumes of about 7110 m3 s−1 were at the minimum for the spawning of A. sinensis. The Three Gorges reservoir operation as designed would satisfy the spawning flows for A. sinensis except in low-flow years. Once low flow years occur, an adaptive operational procedure should be taken to meet the A. sinensis spawning requirements for hydrodynamics. This can be achieved by impounding water early on and taking rapid responses to meet the flow at the spawning time of A. sinensis.