Yichang Station Research Articles

A multiscale attribution framework for separating the effects of cascade and individual reservoirs on runoff

Climate change and human activities have great impacts on runoff. With the gradual development of cascade hydropower in the watershed, the reservoirs have increasingly impacted runoff. However, the current study mainly focuses on quantifying the impacts of human activities and climate change on runoff, lacking the exploration of the impacts of cascade reservoirs, and the attribution results are relatively rough. Therefore, this study utilized data-driven models to establish a runoff attribution framework with the basic steps of “interval runoff prediction and scheduling rule extraction”, which achieved the spatial scale separation of the impacts of cascade and individual reservoirs on the runoff, and the analysis of the impacts of each factor at multiple time scales. Taking the upper reaches of the Yangtze River mainstem as an example, we verified the applicability and accuracy of the framework, explored the impacts of climate change, human activities (without reservoir scheduling), and reservoir scheduling on runoff during the period 1980–2018. The research found: (1) Compared to the base period 1980–2005, the average multi-year runoff changes at Pingshan Station (during 2013–2018), Yichang Station (during 2006–2012) and Yichang Station (during 2013–2018) were − 2.61 %, −4.33 % and − 0.89 %, respectively, with decreasing, increasing, and flattening trends over time. (2) Reservoir scheduling is the main factor leading to runoff change, showing negative impacts during flood season and positive impacts during non-flood season. (3) Under the control domain of single and cascade reservoirs, the annual scale impacts of climate change, human activities, and reservoir scheduling on runoff accounted for approximately 1:1:8 and 2:2:6, respectively, showing a complex nonlinear relationship between the impacts of single and cascade reservoirs on runoff. This study provides ideas for quantitatively assessing the impacts of cascade reservoirs on runoff and provide a basis for comprehensively assessing the ecosystem and socio-economic impacts of reservoirs on future runoff changes.

Using explainable artificial intelligence (XAI) methods to understand the nonlinear relationship between the Three Gorges Dam and downstream flood

Study RegionIn the Yangtze River basin of China. Study focusThe emerging Explainable Artificial Intelligence (XAI) methods provide us an opportunity to understand the nonlinear relationship that the Deep Learning(DL) model learned inside. The construction of the Three Gorges Dam (TGD) has successfully minimized the likelihood of flooding in the Yangtze River basin. The XAI methods can help us to know the nonlinear relationship behind it. We apply the Long Short Term Memory (LSTM) network, in conjunction with two XAI methods, SHapley Additive exPlanation (SHAP) and Expected Gradient (EG), to do our work.In our DL model, we use YiChang (YC) station runoff,Precipitation (Pre) and vapour pressure deficit (VPD) data from the middle and lower river basin as input, while the output of the model generates runoff data at the DaTong (DT) station, XAI methods enable us to calculate the significance of each input feature is for generating the output feature in a DL model. In this study, we examine the difference in importance scores between the Before Three Gorges Dam (BTGD) period and the After Three Gorges Dam (ATGD) period. New Hydrological Insights for the RegionIn the BTGD period, YC runoff was the primary contributor to flooding at the DT station. However, in the ATGD period, the largest contribution to flooding in the middle and lower Yangtze River basin has shifted from YC runoff to the the middle and lower reaches of precipitation. Our results suggest that the XAI can show the nonlinear relationship between the TGD and downstream flood clearly and the TGD can effectively mitigate flooding in the middle and lower river basins by regulating runoff from the upper river basin. The work shows the potential of XAI to explain the nonlinear relationship in the hydrology field.

Comprehensive evaluation of watershed ecohydrological risk and ecohydrological satisfaction characteristics from the perspective of hydrological variability

Abstract This study quantifies the degree of hydrological regime alteration in the middle and lower reaches of the Yangtze River (MLYR) by incorporating the indicators of hydrologic alteration (IHA) along with six additional indicators. The ecohydrological risks are analyzed using the eco-surplus and eco-deficit indicators. Furthermore, the ecohydrological satisfaction index (ESI) is proposed to characterize the degree to which hydrological conditions meet the eco-water demand of rivers. The results indicate that the concentration period is delayed, and the complexity of hydrological processes is increased in the MLYR. Regarding the variability of hydrological conditions, except for Datong station with a change degree below 0.5, the other stations have experienced high changes. At the annual scale, the eco-surplus and eco-deficit of the MLYR basin have changed with the alteration degree of 0.41 and 0.37, respectively, and the eco-deficit of the mainstream exceeds the eco-surplus, indicating high ecohydrological risks. The ESI at Yichang station has significantly decreased, with the most pronounced decrease occurring in February (−0.35). The ESI of tributaries in the MLYR remains stable, with periods when the ESI at Huangzhuang station exceeds 0.8 accounting for more than 80% of the period from 2004 to 2021.

The important role of tributaries and flood events in sediment transport: A study on the spatiotemporal variability of water and sediment discharge upstream and downstream of the Three Gorges Reservoir

After the construction of the cascade reservoirs in the lower Jinsha River, it has become necessary to clarify the spatial and temporal variability of the volume of sediment entering the Three Gorges Reservoir in order to manage sediment within the basin considering the new situation of rapid sediment reduction. Previous studies were affected by the inaccurate analyses of transition points and associated causes and were unable to identify clear changes in the spatial and temporal characteristics. Therefore, the impact that the Three Gorges Reservoir has on sediment reduction in the upper Yangtze River needs to be reassessed. The Lepage test and sediment identity factor method were applied to reveal that the sediment transported by the Jinsha River has significantly decreased since 2013 due to the reservoir construction, while the sediment transported by the Min River and Jialing River has slightly increased since 2014 and 2015 due to heavy rainfall. However, this has ultimately led to a significant reduction in sediment entering the Three Gorges Reservoir since 2013. Accordingly, the spatial composition of sediment sources in the Three Gorges region has been dominated by tributaries in recent years, with the Jialing River accounting for 38.98 % of the total and the Jinsha River accounting for only 1.74 %. Under these new conditions, sediment transported during short-term floods becomes more important, with sediment entering the Three Gorges Reservoir during 7 day flood events accounting for up to 47.16 % of the total transport in a year. As a result of sediment trapping by the upstream reservoirs, the Three Gorges Reservoir is responsible for only 7.5 % to 22.75 % of the sediment reduction observed at Yichang Station. Understanding the weakened impact that the Three Gorges Reservoir has on the sediment reduction phenomenon in the upper Yangtze River is important for managing the schedules of the reservoirs in the upper Yangtze River.

Driving forces of hydrological health and multifractal response of fish habitat in regulated rivers

Climate change and anthropogenic activities are major influences on the hydrological cycle, further altering river hydrological health. However, the characteristics of the forces in driving the variations of hydrological health at long-short time scales (annual, seasonal, monthly), as well as the potential impacts of these variations on aquatic habitats, remain unclear. In this study, the flow threshold method was introduced to identify the inherent characteristics of river hydrological health degree (RHD) evolution in the upper reaches of the Yangtze River (URYR) through the extreme-point symmetric modal decomposition (ESMD) method and range of variation approach (RVA). The RHD under unregulated conditions was reconstructed to quantify the impacts of anthropogenic activities and climate change. Subsequently, a multifractal model was proposed to establish the relationship between RHD and habitat-weighted usage area (WUA) during the spawning period of the Four Famous Major Carps, aiming to analyze the response mechanisms of habitat conditions to RHD fluctuations. The results showed that the RHD in the URYR exhibited degradation characteristics, experiencing a moderate change with a value of 0.44. Climate change was identified as the dominant factor causing the annual-scale decline in RHD, with an average impact weight of 62.9%. At the annual scale, Anthropogenic activities exacerbate (−3.4), counteract (20.1), and counteract (20.5) the adverse climatic impacts at Yichang, Cuntan, and Zhutuo stations, respectively. Additionally, the effect of human activities during the flood season is slight, with the most favorable and unfavorable impacts occurring in December (50.7) at the Zhutuo station and in October (−27.2) at the Yichang station. Under the influence of driving forces, the multifractal correlation of the RHD-WUA system tended to homogenized as the time window increased, indicating the presence of potential nonlinear dependence, asymmetric fractal characteristics, and positive-to-negative persistence transitions. Therefore, modeling river health considering fish habitat cannot be limited to linear paradigms. The findings provide valuable insights for the management and restoration of aquatic ecosystems.

Study on a mother wavelet optimization framework based on change-point detection of hydrological time series

Abstract. Hydrological time series (HTS) are the key basis of water conservancy project planning and construction. However, under the influence of climate change, human activities and other factors, the consistency of HTS has been destroyed and cannot meet the requirements of mathematical statistics. Series division and wavelet transform are effective methods to reuse and analyse HTS. However, they are limited by the change-point detection and mother wavelet (MWT) selection and are difficult to apply and promote in practice. To address these issues, we constructed a potential change-point set based on a cumulative anomaly method, the Mann–Kendall test and wavelet change-point detection. Then, the degree of change before and after the potential change point was calculated with the Kolmogorov–Smirnov test, and the change-point detection criteria were proposed. Finally, the optimization framework was proposed according to the detection accuracy of MWT, and continuous wavelet transform was used to analyse HTS evolution. We used Pingshan station and Yichang station on the Yangtze River as study cases. The results show that (1) change-point detection criteria can quickly locate potential change points, determine the change trajectory and complete the division of HTS and that (2) MWT optimal framework can select the MWT that conforms to HTS characteristics and ensure the accuracy and uniqueness of the transformation. This study analyses the HTS evolution and provides a better basis for hydrological and hydraulic calculation, which will improve design flood estimation and operation scheme preparation.

Simulation of Water Level and Flow of Catastrophic Flood Based on the CNN-LSTM Coupling Network

The occurrence of catastrophic floods will increase the uncertainty of hydrological forecasting at downstream hydrological stations. In order to solve the problems of the unclear propagation law of catastrophic floods in the middle and lower reaches of the Yangtze River and the inadaptability of traditional forecasting methods, this paper uses the M-K trend test method to analyze the annual average flow and annual average water level of the Yichang and Hankou stations. For conventional floods and catastrophic floods, Random Forest (RF), Convolutional Neural Network (CNN), Long Short-Term Memory Network (LSTM), and CNN-LSTM neural networks are used to simulate the water level/flow of Hankou station. The simulation results are analyzed by Nash–Sutcliffe Efficiency Coefficient (NSE), Kling–Gupta efficiency coefficient (KGE), Root Mean Square Error (RMSE), and Symmetric Mean Absolute Percentage Error (SMAPE). The results show that the annual average flow and annual average water level of Yichang station show a downward trend and the annual average water level of Hankou station shows an upward trend. By comparing the four indicators of NSE, KGE, RMSE, and SMAPE, the CNN-LSTM coupling model was determined to be the best fitting model, with NSE and KGE greater than 0.995 and RMSE and SMAPE less than 0.200. The proposed coupling model can provide technical support for flood control optimization, scheduling, emergency rescue, and scheduling impact analysis of the Three Gorges Power Station.

Disproportional erosion of the middle-lower Yangtze River following the operation of the Three Gorges Dam

The operation of the Three Gorges Dam (TGD) modifies downstream flow and sediment regimes, triggering disproportional fluvial responses at different distances downstream. However, our understanding of the downstream geomorphic changes in the middle-lower Yangtze River remains incomplete due to the complexity of the river responses across temporal and spatial scales. Here, we leverage data on discharge, suspended sediment concentration (SSC), riverbed grain size, cross-sectional profiles and high-resolution channel bathymetric maps at different locations downstream of the TGD to investigate geomorphic responses. The results show that the magnitude of fluvial erosion decreases downstream, with the Yichang-Luoshan Reach (the first ~500 km downstream) experiencing the most severe erosion in 2003–2020 (~9.05 × 104 t/km/yr). Local changes in riverbed morphology include channel bar erosion, channel incision (~0.43 m/yr in CS1 near the dam site over 2002–2019), riverbank retreat and bed material coarsening (an increase in D50 from 0.175 to 43.1 mm at Yichang station from 2002 to 2017). Such marked erosion is caused by the sharply reduced SSC in the dominant discharge range (10,000–30,000 m3/s) and the extended duration of this dominant discharge range. The sediment erosive magnitude in the Luoshan-Datong Reach is relatively small (3.85 × 104 t/km/yr) in 2002–2020. The Luoshan-Hukou Reach (~500–1000 km downstream) exhibits moderate channel incision, minor bed material coarsening and moderate mid-channel bar lateral erosion. The Hukou-Datong Reach (below 1000 km downstream) experienced minor geomorphic change without significant evidence of bed material coarsening. The relatively small impact of the TGD on the lower reach from Luoshan to Datong can be mainly attributed to the progressive SSC recovery along the river induced by upstream channel erosion providing sediment replenishment. These findings have significant implications for estimating geomorphic changes in response to upstream damming and thus could inform better river management and ecological assessment in other similar alluvial rivers.

Dam Impacts on Seasonality of Water and Sediment Transport in Intensively Managed River Basins: A Case Study of the Yangtze River

AbstractExtensive studies have been performed on water and sediment transport of the Yangtze River in recent decades, but very few studies were focused on seasonal and daily variations. After the construction of Three Gorges Dam (TGD) in 2003, several key cascade dams were built on the Yangtze upstream. Annual, monthly, and daily data were used to study the seasonality change on water level, water discharge, and sediment load in response to multiple reservoir impoundments. TGD impacted the water level inside the reservoir greatly by shifting the peak water level from summer to winter and made the hydrograph more asymmetrical. In contrast, minor changes in water levels (<2 m) occurred at stations downstream of the TGD mainly due to channel incision. Downstream of TGD at Yichang station, annual hydrograph was flattened slightly: water discharge in the dry season increased 49% whereas that of flood season decreased 14% from 1956–2002 to 2013–2017. Mean annual water discharge downstream of the TGD was slightly impacted because the impounded water was <5% of annual inflow of the reservoir. Comparing with the Yangtze, the annual hydrographs of other intensively managed rivers like the Yellow, Missouri, and Colorado have been flattened more effectively by reservoir impoundments. The sediment rating curves at Yichang and Hankou changed from an oval‐like shape before 2013 to two overlapping and flattened lines in 2013–2017. This shift indicates that the rising and falling limbs of the hydrograph experienced similar sediment concentrations in 2013–2017 and suggests a less obvious hysteresis effect. Over 50% of the sediment load observed at the seaward‐most Datong station was contributed by the large tributaries in the upper reach, like Jinsha and Jialing rivers, before 2003. The channel scour downstream of TGD contributed 49%–64% of the Datong sediment load after 2003.

Multi-scale variability of hydrothermal regime based on wavelet analysis - The middle reaches of the Yangtze River, China

Water temperature is a major driver of riverine ecosystems and has an extremely significant impact on them. Understanding the multi-scale water temperature dynamics in a river basin is critical to analyze the water temperature status of rivers. In this study, the intra-annual and inter-annual time series of water temperature (WT) at Yichang station in the middle reaches of the Yangtze River over the past 62 years was analyzed using complex Morlet wavelet functions to reveal the complex structure of water temperature variation at multiple time scales. The ecological impact of water temperature changes on the reproduction of the “Four Major Chinese Carp” under the influence of the Three Gorges Dam (TGD). The results showed that the water temperature at Yichang Station has a multi-level time scale structure, with an increasing trend at the inter-annual scale from 1956 to 2017, but different variations at the seasonal scale, and the water temperature cycles at both the inter-annual and seasonal scales have time scale variations of about 8–14 years and 4–7 years, with obvious characteristics of WT variation stages. The inter-annual and summer scales will have low WT in 2017–2022 and high WT in 2023–2027, while the other seasonal scales will have high WT in the next few years, either in the short or medium term. The correlation between air temperature and WT is the most significant among the three drivers of air temperature, flow and rainfall, and the correlation between WT and the air temperature is the most significant in winter scale under the influence of the Three Gorges Dam construction. Since the completion of TGD in 2003, the summer drainage temperature has decreased and the breeding period of the “Four Major Chinese Carp” has been shortened by 30–40 days compared to that before the construction of TGD. The results of this study can be used as a basis for further exploration of the formation mechanism of river water temperature and provide a scientific basis for river ecological protection.

Evaluation of hydrological regime alteration and ecological effects in the middle and lower of the Yangtze River, China

Abstract The flow regime is regarded as the key driver of the structure and function of riverine ecosystems. This study uses an ecologically meaningful indicator (range of variability approach method) to assess the dynamic runoff process in the middle and lower reaches of the Yangtze River, whose changes negatively affect the ecosystems in the study area. In addition, the study quantitatively analyzed the contribution rate of human activities and climate change to flow change. The effects of ecological index changes on four famous major carp species (FFMC) resources in the middle and lower reaches of the Yangtze River were studied. The results show that after the Three Gorges Dam (TGD) operation, the hydrological changes of Yichang Station, Hankou Station, and Datong Station were 65, 58, and 46%, respectively. The weight of the impact of human activities on runoff is smaller the farther away from the TGD. The impact weights of human activities at the three hydrological stations in the middle and lower reaches of the Yangtze River are 73.69, 67.98, and 56.84%, respectively. The operation of the Three Gorges Project caused changes in the hydrological regime of the Yangtze River, which adversely affected the structure and quantity of FFMC populations.

Impacts of climate and reservoirs on the downstream design flood hydrograph: a case study of Yichang Station

Impacts of climate and reservoirs on the downstream design flood hydrograph: a case study of Yichang Station

Study of the Three Gorges Dam’s Impact on the Discharge of Yangtze River during Flood Season after Its Full Operation in 2009

The impact of the Three Gorges Dam (TGD) on the discharge after its first operation in 2003 has drawn much attention. Most of the existing research focuses on the TGD’s impact after its initial operation in 2003. However, the water level first reached the TGD’s maximum water level, 175 m, in September 2009. In this paper, to quantify the TGD’s impact during flood season after its full operation in 2009, we created a hydrological model to reconstruct the daily discharge unregulated by the TGD from 2003 to 2018 at the five stations downstream from the TGD. The TGD had an impact on the maximum 1-day discharge and maximum 30-day runoff and the coefficient of variation of the daily discharge, but it had less impact on the flood season runoff and the coefficient of skewness of the daily discharge. Additionally, the TGD was only responsible for 18.3% of the change in the maximum 1-day discharge at the Datong station, which is 1123 km downstream from the TGD. Moreover, the TGD had limited impact on the discharge after its initial operation in 2003, but the impact of the TGD on discharge increased after its full operation in 2009. This study helps to show the TGD’s impact on the discharge of the Yangtze River from the Yichang station (43 km downstream from the TGD) to the Datong station.

Spatio-Temporal Variability in Hydroclimate over the Upper Yangtze River Basin, China

As global warming produces dramatic climate changes, water management is facing increasingly serious challenges. Given to the process of climate change and its complex effects on watershed hydrology, this paper investigates the spatial and temporal variation characteristics of major climatic factors (i.e., precipitation and temperature) over the upper Yangtze River basin (UYRB), China. The statistical analyses are based on annual and seasonal scales during 1951–2020 with a recorded period of seven decades. The Mann–Kendall nonparametric test and R/S analysis are used to record the temporal trends (past and future) of climate variables; the Pettitt test, standard normal homogeneity test and Buishand test are used to detect the homogeneity in climate series. The sensitivities of the streamflow to climatic parameters are assessed at the watershed scale, especially considering the Three Gorges Dam’s (TGD) effect on changing runoff. The results of the study indicate that the annual precipitation of 29 out of 34 series indicate homogeneity, while 31 out of 34 annual mean temperature series show heterogeneity, with jump points around 1997 in the mean temperature of 20 sites. Detectable changes in precipitation were not observed during 1951–2020; however, the temperature increased significantly in the whole basin on annual and seasonal scales, except for several stations in the eastern part. The magnitude of increase in air temperature in high altitudes (Tibet Plateau) is higher than that in low altitudes (Sichuan Plain) over the last seven decades, and future temperatures continue to sharply increase in high altitudes. The TGD plays an important role in explaining the seasonal variations in streamflow at Yichang station, with streamflow experiencing a sharp increase in winter and spring (dry season) and a decrease in summer and autumn (rainy season) compared to the pre-TGD period. The streamflow variation at an annual scale is mainly regulated by climate fluctuation (variation in precipitation). During the last seven decades, increasing air temperature and decreases in rainfall and runoff signify reduced water resources availability, and the climate tends to be warmer and drier over the basin. The sensitivity of the streamflow to watershed precipitation is higher than that to temperature, with variation in annual rainfall explaining 71% of annual runoff variability.

Hydrological drought evolution and its response to meteorological drought in the middle-lower reach of the Yangtze River triggered by Three Gorges Reservoir

利用1960—2016年长江流域183个气象站逐月气温和降水数据以及干流3个水文站逐月径流资料, 采用标准化降水蒸散指数(SPEI)和标准化径流指数(SRI)分析三峡水库蓄水运行前后长江中下游宜昌、汉口和大通站水文干旱的多时间尺度演变以及对气象干旱的响应特征. 结果表明: (1) 三峡水库运行后下游各站冬春季旱情明显趋缓, 而秋季干旱状况略有加重; 水库蓄水后各站中旱和重旱发生频率均呈减少趋势, 其中中旱减幅明显, 而特旱发生频率则总体表现为增加趋势; (2) 三峡水库蓄水后3个站平均干旱历时的变幅相对较小, 而干旱烈度和烈度峰值的均值增幅较大; 同时, 各站短时间尺度(1和3个月) 干旱特征变量的变幅总体呈现沿程递增趋势, 而长时间尺度(6和12个月) 干旱特征变量的变幅整体表现为沿程递减趋势; (3) 水库蓄水后各站短时间尺度SRI与SPEI的相关性减小, 但相关性随时间尺度增加而迅速增强, 12个月时间尺度的相关系数达到最大并略高于蓄水前; 在年内相关性上, 蓄水后各站短时间尺度SRI与SPEI的相关系数明显减小, 冬季表现尤为突出, 而长时间尺度的相关系数则略有增加; (4) 水库影响下不同时间尺度宜昌站水文干旱滞后于气象干旱平均天数有增有减, 而汉口和大通站的滞后天数均呈显著增加趋势, 且总体表现为沿程递增趋势. 研究结果可为变化环境下水文干旱预警与水库优化调度提供参考.;Based on monthly temperature and precipitation data from 183 meteorological stations in the Yangtze River (YZR) Basin and monthly runoff data from three hydrological stations in the mainstream of the YZR during 1960—2016, this study, using the standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI), analyzed the multiple timescales evolution of hydrological drought and its response to meteorological drought at Yichang, Hankou, and Datong stations in the middle-lower reach of the YZR before and after the operation of the Three Gorges Reservoir (TGR). The results showed that with the operation of TGR, drought situations at the downstream hydrological stations in winter and spring were significantly reduced, while drought conditions were slightly aggravated in autumn. The occurrence frequency of moderate and severe drought at each hydrological station showed a declining trend in the post-TGR period, particularly for the moderate drought. The frequency of extreme drought demonstrated an increasing trend in general. With the TGR was impounded, the average drought duration of three hydrological stations showed relatively mild variations, whereas the average drought severity and peak exhibited a significant upward trend. Furthermore, the variation amplitude of drought characteristic variables at the short-term timescale (1 and 3 months) from three hydrological stations displayed an increasing trend along the middle-lower reach of the YZR, while decreasing trend happened at the long-term timescale (6 and 12 months). The correlation between SRI and SPEI series from three hydrological stations at short-term timescale decreased significantly, but the correlation increased rapidly with timescale increase. Correlation coefficient between the SRI and SPEI series reached the maximum at 12-month timescale and were slightly higher than that in the pre-TGR period. Meanwhile, the intra-annual correlation coefficients between the SRI and SPEI series at the short-term timescale declined evidently in the post-TGR period, particularly in winter. However, the correlation coefficients of the SRI and SPEI series at long-term timescale increased slightly. With the impacts of the TGR, average day number that hydrological drought lagged behind meteorological drought at Yichang station at different timescales increased or decreased, while the number of lagged days at Hankou and Datong stations increased significantly, and had an increasing trend along the middle-lower reach of the YZR. These results can provide reference for hydrological drought warning and optimal operation of reservoir under the changing environment.

A nonstationary bivariate design flood estimation approach coupled with the most likely and expectation combination strategies

In this study, a framework is proposed to estimate the nonstationary bivariate design flood, which includes three key steps. First, a nonstationary copula model was constructed to analyze the temporal variation in the bivariate joint distribution. Second, the equivalent reliability method was used to calculate the design value of the dominant variable for a return period and the design lifespan length under non-stationarity. Third, the design value of the secondary variable that was conditioned on the design value of the dominant variable, was calculated using the conditional most likely combination and conditional expectation combination strategies. Through the above three steps, the typical design value combination of the nonstationary bivariate was obtained for a specific design standard. A case study, based on the nonstationary annual maximum 1-day (AM1) and 15-day (AM15) flood volume at the Yichang station, was conducted to illustrate the framework. The results indicate that the joint distribution of the AM1 and AM15 flood volumes varied over time. For a specific design standard, the design values of the AM15 and AM1 flood volumes decreased with an increase in the design lifespan length. Moreover, the conditional most likely estimation of the design value for the AM1 flood volume that was conditioned on the design value for the AM15 flood volume was greater than its conditional expectation estimation.

Investigation on joint mining of Rare earth elements and zircons from the Yangtze River, China

Rare earth elements(REEs) have attracted much attention in recent years. China is the leading supplier of REEs, thanks to its vast mineral reserves and technological innovation since the 1960s. In the same period, China’s sand used in construction has also increased year by year. The integrated application of the full utilization of sand for construction and exploration and mining engineering of REEs have been the subject of many recent studies. This paper compares the main erosion areas of the Changjiang River. And the abundance of zircon, a byproduct of heavy rare earth elements in different regions. Yichang station is considered as a possible mining site. According to the characteristics of mechanical separation process and hydrometallurgy, a comprehensive system of river sand mining and REEs extraction was designed. This system is well established in zircon mining(LCA). However, the REEs extraction of river sand is affected by mineral composition, which requires a large number of experiments to optimize the process. This area needs further research.

A Statistical Hydrological Model for Yangtze River Watershed Based on Stepwise Cluster Analysis

Streamflow prediction is one of the most important topics in operational hydrology. The responses of runoffs are different among watersheds due to the diversity of climatic conditions as well as watershed characteristics. In this study, a stepwise cluster analysis hydrological (SCAH) model is developed to reveal the nonlinear and dynamic rainfall-runoff relationship. The proposed approach is applied to predict the runoffs with regional climatic conditions in Yichang station, Hankou station, and Datong station over the Yangtze River Watershed, China. The main conclusions are: 1) the performances of SCAH in both deterministic and probabilistic modeling are notable.; 2) the SCAH is insensitive to the parameter p in SCAH with robust cluster-tree structure; 3) in terms of the case study in the Yangtze River watershed, it can be inferred that the water resource in the lower reaches of the Yangtze River is seriously affected by incoming water from the upper reaches according to the strong correlations. This study has indicated that the developed statistical hydrological model SCAH approach can characterize such hydrological processes complicated with nonlinear and dynamic relationships, and provide satisfactory predictions. Flexible data requirements, quick calibration, and reliable performances make SCAH an appealing tool in revealing rainfall-runoff relationships.

Changes in Flood Regime of the Upper Yangtze River

River flooding affects more people worldwide than other natural hazards. Thus, analysis of the changes in flood regime caused by global warming and increasing anthropogenic activities will help us make adaptive plans for future flood management. The nonstationary flood behavior in the upper Yangtze River was examined comprehensively in terms of trend, change point, and periodicity with co-usage of different methods. Results show that there are decreasing tendencies in the corresponding series of annual maximum flood peak flow and flood volume in four out of six control stations, except Pingshan and Wulong stations in the Jinsha River and the Wu River, respectively, and the flood peak occurrence time appears earlier mostly. The uniformity of flood process increases in four main tributaries, while it decreases in mainstream of the Yangtze River (Yichang and Pingshan stations). The rates of both rising limb and recession limb of all the typical flood process flowing through the six stations were analyzed. 77.8% of the rates of rising limb decrease, while 61.1% of the rates of recession limb increase, which is almost consistent with the variation reflected by the uniformity. The change points of most evaluation indicators happened in 1970s–1990s. The first main periodicity of evaluation indicators in Yichang is about 45 years, while that of other stations is about 20 years. Invalidity of stationarity in the flood series can be attributed to the intensified construction on major water conservancy projects, changes of underlying surface, and influences of climatic variables. The contributions of both climatic control and the Three Gorges Dam (TGD) to the variation of the annual flood peak in Yichang station were further quantitatively evaluated, which has verified that the construction of the TGD has played a positive role in peak-flood clipping.

A C-vine copula framework to predict daily water temperature in the Yangtze River

The thermal regime of rivers plays a crucial role in chemical, biological and ecological processes. Effectively predicting water temperature is a key issue related to environment management. This study develops a probabilistic model based on C-vine copulas for water temperature prediction. The proposed framework is applied to forecast daily water temperature in the Yangtze River, considering long-term effects of preceding air temperature and daily discharge. The prediction performance of this framework is compared with the logistic regression model (LogR) and generalized regression neural network (GRNN). The results of this study indicate that the proposed C-vine copula framework and GRNN model provide better forecasting of stream temperature with weak human-related disturbances than LogR model. The outperformance of C-vine framework is reflected by its ability to accurately capture variations in the water temperature greatly affected by the Three Gorges Reservoir (TGR). This steady and reliable framework is further applied for the conservation of Chinese Sturgeon to estimate the range of suggested discharge, given the daily air temperatures, to adjust the water temperature within 18–20 °C at Yichang station during the spawning season. This application is verified to be more effective, providing indications for reservoir management to lower water temperatures by regulating river flow to ensure the occurrence of spawning activities. The results of this study may provide a scientific reference for the ecological operation of reservoirs in regulated rivers.