Optimized operation of cascade reservoirs on Wujiang River during 2009-2010 drought in southwest China

The effects of optimized operation principles implemented at reservoirs on the Wujiang River in southwest China between September 2009 and April 2010 under drought conditions were analyzed based on operational data collected from the Guizhou Wujiang Hydropower Development Co., Ltd. A set of linear regression equations was developed to identify the key factors impacting the electric power generation at reservoirs. A 59% reduction in the inflow discharge at the Hongjiadu Reservoir led to a decrease of only 38% in the total electric power generation at the Hongjiadu, Dongfeng, Suofengying, and Wujiangdu reservoirs on the Wujiang River, indicating that optimized operation can play an important role in drought management. The water level and the amount of other water inputs at the Hongjiadu Reservoir and the outflow discharge at all of the reservoirs except the Wujiangdu Reservoir were key factors affecting the total electric power generation at reservoirs on the Wujiang River under optimized operation.

Influence of cascade reservoirs on spatiotemporal variations of hydrogeochemistry in Jinsha River

River hydrogeochemistry offers necessary guidance for effective water environmental management.However,the influence of cascade reservoirs on river hydrogeochemistry remains unknown.In this study,the Jinsha River,the headwaters of the Yangtze River of China,was selected to investigate the spatiotemporal variations of hydrogeochemistry after the construction of six cascade reservoirs.Major ions,total dissolved solids,electrical conductivity,and pH values of sampled water in the upper natural reaches and lower reservoir-regulated reaches were analyzed in both flood and dry seasons.The results of Piper diagram and Gibbs plots showed that the hydrogeochemistry of the Jinsha River was naturally controlled by both evaporation-crystallization and carbonate weathering processes,but it was also artificially affected by reservoirs.The impoundment of cascade reservoirs affected the hydrodynamic condition of the river.The river flow in the flood season was reduced by approximately 24.5%,altering the proportions of water sources and leading to notable hydrogeochemical alterations in reservoir-regulated reaches.Conversely,river hydrogeochemistry generally remained unchanged in the dry season,owing to the insignificant effect of cascade reservoirs on river flow.In contrast to what has been observed in previous studies of individual reservoirs,the cumulative influence of cascade reservoirs on the Jinsha River flow regime did not cause abrupt hydrogeochemical changes between the upstream and downstream areas of each reservoir.Moreover,the water quality assessments revealed that the impoundment of cascade reservoirs improved downstream irrigational water quality,with lower Naþratio values in the flood season.This study provides the earliest evaluation of cascade reservoir influence on the hydrogeochemistry of the Jinsha River.The findings of this study can be used as a reference for scientific guidelines for future environmental management of cascade reservoirs in large rivers.

Diurnal variations of pCO_2 in relation to environ-mental factors in the cascade reservoirs along the Wujiang River, China

We have investigated the diurnal variations of the pCO2 and related environmental factors in the cascade reservoirs with different trophic levels along Wujiang River. In surface water the pCO2 was 357±11 μatm in Hong-jiadu Reservoir, 338±48 μatm in Dongfeng Reservoir, 682±303 μatm in Wujiangdu Reservoir, and 1677±429 μatm in Liuguang, respectively. The results indicated that these cascade reservoirs had much lower pCO2 values in surface water than river did, and hypereutrophic reservoir showed larger diurnal variations of pCO2 than meso-eutrophic reservoir. In water column, pCO2 tended to increase with the depth. Phytoplankton and the environmental factors such as temperature and pH had different influences on pCO2 diurnal variations due to different trophic levels, and the effect of phytoplankton on pCO2 variation increased with the increase of trophic level in these reservoirs.

Numerical Simulation of Dam-Break Flooding of Cascade Reservoirs

Previous studies at home and abroad have mainly focused on single dam-break, and little attention has been paid so far to the dam-break of cascade reservoirs. Multi-source flooding, which can lead to three-dimensional turbulent phenomena and superposition effects, is the main difference between the dam-break of cascade and single reservoirs. Detailed descriptions of the coupled numerical simulation of multi-source flooding have little been reported, and the initial wet riverbed is rarely considered in current models. Therefore, in this paper, a method based on the three-dimensional (Formula presented.) turbulence model coupled with the volume-of-fluid method is proposed to simulate the dam-break flooding of cascade reservoirs. The upstream river, reservoir, and downstream river are connected by the internal boundary method, and the initial conditions, including river flow and reservoir water, are determined according to the results of the numerical simulation. Coupled numerical simulation of different dam-break flooding is then achieved. The present work solves the challenges presented by the enhancement and superposition of natural river flow, upstream flooding, and downstream flooding. This paper provides a theoretical basis for future studies on the dam-break flood routing of cascade reservoirs. © 2017 Tianjin University and Springer-Verlag GmbH Germany

Identification of terrigenous and autochthonous organic carbon in sediment cores from cascade reservoirs in the upper stream of Pearl River and Wujiang River,southwest China:lignin phenol as a tracer

Organic carbon(OC)source attribution for cascade reservoir sediments has been identified as a critical gap in understanding the effective carbon sink of inland waters.In this study,nine sediment cores were collected from cascade reservoirs in the Wujiang and Pearl Rivers.We analyzed lignin phenol(Λ8),total organic carbon(TOC)content,and stable carbon isotopic composition(δC)of the sediments,focusing on the changes of terrigenous OC,and the variation of OC source in cascade reservoir sediments after damming.Our results showed that theΣ8 and TOC contents decreased from upstream to downstream reservoirs,indicating the significant interception of terrigenous OC by cascade damming.Additionally,theΛ8 content in the Pearl River reservoir sediments was much higher than that in the Wujiang River.From the three-end-member mixing model,we estimated that OC in reservoir sediments mainly comes from soil and plankton.After damming,the proportion of plankton OC in TOC slightly increased in seasonal and annual regulation reservoirs due to the limnetic evolution of the reservoir.These findings suggest that the cascade damming increases the interception capacity of the river to terrigenous OC and nutrients,and that slowing of water velocity caused by damming affected primary productivity and fluvial carbon cycling.

FORECASTING OF A NONLINEAR CASCADE FOR WATERSHED RUNOFF

Forecasting of a nonlinear cascade was developed for modeling watershed runoff, and was tested by computing the direct runoff hydrograph for two rainfall- runoff events on a small watershed in China . The forecasting model was superior to Ding s variable unit hydrograph method and the method of limited differences for these two events.

Optimal Scheduling of Cascaded Hydrothermal Systems Using a New Improved Particle Swarm Optimization Technique

Optimum scheduling of hydrothermal plants generation is of great importance to electric utilities. Many evolutionary techniques such as particle swarm optimization, differential evolution have been applied to solve these problems and found to perform in a better way in comparison with conventional optimization methods. But often these methods converge to a sub-optimal solution prematurely. This paper presents a new improved particle swarm optimization technique called self-organizing hierarchical particle swarm optimization technique with time-varying acceleration coefficients (SOHPSO_TVAC) for solving short-term economic generation scheduling of hydrothermal systems to avoid premature convergence. A multi-reservoir cascaded hydrothermal system with nonlinear relationship between water discharge rate, power generation and net head is considered here. The performance of the proposed method is demonstrated on two test systems comprising of hydro and thermal units. The results obtained by the proposed methods are compared with other methods. The results show that the proposed technique is capable of producing better results.

EXPERIMENTAL STUDY OF DAM-BREAK FLOW IN CASCADE RESERVOIRS WITH STEEP BOTTOM SLOPE

Dam break can cause a significant disaster in the downstream, especially, in a valley with cascade reservoirs, which would aggravate the disaster extent. The experimental studies of the dam-break flow of cascade reservoirs are few and far between at the present, Most of related studies concern the failure of a single dam.. This article presents an experimental study of the characteristics of an instantly filled dam-break flow of cascade reservoirs in a rectangular glass flume with a steep bottom slope. A new method was used to simulate the sudden collapse of the dam. A series of sensors for automatic water-levels were deployed to record the rapid water depth fluctuation. The experimental results show that, the ratio of the initial water depth of the downstream reservoir to that of the upstream reservoir would greatly affect the flood peak water depth in the downstream reservoir area and in the stream channel behind the downstream dam, while the influence of the dam spacing is insignificant. In addition, the comparison between the single reservoir and the cascade reservoirs shows some difference in the dam-break flow pattern and the stage hydrograph at the corresponding gauging points.

Evaluation of optimization operation models for cascaded hydropower reservoirs to utilize medium range forecasting inflow

This paper evaluates the performances of the models that incorporate forecasting inflow for cascaded hydropower reservoirs operation. These models are constructed separately on the concepts of explicit stochastic optimization （ESO） and implicit sto- chastic optimization （ISO） as well as parametefization-simulation-optimization （PSO）. Firstly, the aggregation-disaggregation method is implemented in ESO models to reduce the complexity of stochastic dynamic programming （SDP）. And the aggre- gate flow SDP （AF-SDP） and aggregation-disaggregation SDP （AD-SDP） are constructed respectively. Secondly, in ISO mod- el, decision tree is the well-known and widespread algorithm. The algorithm C 5.0 is selected to extract the if-then-else rules for reservoir operation. Thirdly, based on the PSO model, the hedging rule curves （HRCs） are pre-defined by fusing the storage and inflow as state variable. The parameters of the HRCs are determined by using the simulation-optimization model. Finally, China＇s Hun River cascade hydropower reservoirs system is taken as an example to illustrate the efficiency and reliability of the models. In addition, the values of quantitative precipitation forecasts of the global forecast system （10 days lead-time） are implemented to forecast the 10 days inflow.

Ecologically-friendly operation scheme for the Jinping cascaded reservoirs in the Yalongjiang River, China

Ecologically-friendly reservoir operation pro- cedures aim to conserve key ecosystem properties in the rivers, while minimizing the sacrifice of socioeconomic interests. This study focused on the Jinping cascaded reservoirs as a case study. An optimization model was developed to explore a balance between the ecological flow requirement （EFR） of a target fish species （Schizothorax chongi） in the dewatered natural channel section, and annual power production. The EFR for the channel was determined by the Tennant method and a fish habitat model, respectively. The optimization model was solved by using an adaptive real-coded genetic algorithm. Several operation scenarios corresponding to the ecological flow series were evaluated using the optimization model. Through comparisons, an optimal operational scheme, which combines relatively low power production loss with a preferred ecological flow regime in the dewatered channel, is proposed for the cascaded reservoirs. Under the recommended scheme, the discharge into the Dahewan river reach in the dry season ranges from 36 to 50 m3/s. This will enable at least 50% of the target fish habitats in the channel to be conserved, at a cost of only 2.5% annual power production loss. The study demonstrates that the use of EFRs is an efficient approach to the optimization of reservoir operation in an ecologically friendly way. Similar modeling, for other important fish species and ecosystem functions, supplemented by field validation of results, is needed in order to secure the long-term conservation of the affected river ecosystem.

Dissolved inorganic carbon and its isotopic differentiation in cascade reservoirs in the Wujiang drainage basin

Three cascade reservoirs,built in different periods of time in the Wujiang drainage basin,were inves-tigated in this study.Samples were taken at the surface and also at 20,40,60,80 m depths in front of the dams in April,July,October of 2006 and January of 2007.Chemical parameters were calculated and the concentrations of dissolved inorganic carbon DIC and its isotopic composition(δ13CDIC) were de-termined.In surface waters,the δ13CDIC values are high in summer and autumn and low in winter and spring,while the DIC concentrations are relatively low in summer and autumn and relatively high in winter and spring.In the water column,the DIC concentrations increase while δ13CDIC values decrease with water depth.DIC in various reservoirs is significantly different in isotopic composition from that in natural rivers,but is close to that in natural lakes.In addition,in surface waters,the δ13CDIC values tend to become lower whereas the nutrition level tends to become higher with increasing age of the reser-voirs.The conclusion is that after dam blocking,changes took place in the hydrochemical properties of river water,and the impounding rivers developed toward lakes and swamps.In addition,differentiation in DIC isotopic composition may be used to some extent to trace the evolution process of a reservoir.

基于改进NSGA-Ⅱ算法的梯级水库多目标优化调度

针对在时间步长较小、计算时段数目较多时,传统智能优化算法在求解梯级水库联合优化调度问题上效率低甚至无可行解的问题,提出了一种改进NSGA-Ⅱ算法。该算法基于NSGA-Ⅱ算法框架,引入参考目标值、潜力目标值、偏移度以及变异引导算子来优化种群进化过程,强化迭代中的种群质量,使获得的解集更加接近真实的Pareto前沿。福建省金溪流域梯级水库多目标优化调度实例验证结果表明,改进NSGA-Ⅱ算法相对其他算法运算效率更高,优化结果更好,具有较好的实用性。

Study on joint optimization operation scheme forPangduo reservoir and Zhikong reservoir

The cascade hydropower system composed of Pangduo reservoir and Zhikong reservoir are formed on the middlereach of the main Lasahe river. For giving full play of joint compensation effect of the two reservoirs, the paper studied the joint operationscheme for Pangduo reservoir and Zhikong reservoir. Based on the respective operation scheme, a reservoir group joint operationmodel is built, the model is solved by the simulation- optimization method, and then the practical and operational scheme isachieved. The scheme could give full play of the joint regulation and storage effect of the reservoir group and improve effectivelythe utilization factor of hydropower resources.

Historical Evolution of the Trophic and Limnological Relationships in the Itaipu Reservoir:Top-Down and Bottom-Up Effects upon Fish Production

Many experimental studies have contributed to the development of the theory of trophic chains in lacustrine habitats. They have revealed the important role played by fish, a subject that has been mostly ignored by limnological studies for the past few decades. Most of these studies were developed in Europe and in the United States. The general applicability of this theory has not yet been tested in subtropical and tropical habitats. In spite of controversies, the bottom-up: top-down trophic cascade hypotheses are the most adopted conceptual models. In this context, we examined if these hypotheses may be corroborated by data from the subtropical Itaipu Reservoir. A negative effect was verified between water transparency and total suspended solids. The detritivorous fish exerted a controlling effect on chlorophyll-a concentrations. Bottom-up effects were detected in four trophic levels, and top-down was detected in just one trophic level. The limnological variates influenced the chlorophyll-a concentration, which indicated that the lnTKN plus the effect of the quarter and the reservoir zone (and their interaction) were important.

长江梯级水库群联合调度成效、挑战及对策

经过70 a的建设,长江流域控制性水库群基本建成。以三峡水库为核心的梯级水库群联合调度已经开展10 a。在总结控制性水库群在防洪、供水、生态和应急联合调度取得成绩的基础上,分析控制性水库群及与水网工程联合调度面临的问题和挑战,提出了相应的对策建议。研究表明:水库群联合调度因流域防洪调度而启,目前在防洪、抗旱供水、生态环境和应急等公益调度中发挥了重要作用。气候变化及水文中长期预报不确定性是联合调度面临的主要挑战,其次是水库群联合调度与单个水库多目标调度利益协调、定量评价调度效果及合理的补偿等管理问题。加强“四预”是解决气候变化和人类活动不确定性的主要对策。水库群与水网工程联合调度可以更广泛地发挥水利工程水安全保障作用。建立科学合理的水工程群联合调度体制和机制是解决联合调度管理问题的有效措施。

Eutrophication Indexes Used as Fish Production Parameters in the Itaipu Reservoir(Brazil)

The knowledge of liminology can be applied in studies of trophic state indexes and morfoedaphic indexes as factors for determining the inference fish production in reservoirs. This work is based on the hypothesis of the trophic cascade relations, particularly related to bottom-up and top-down effect in Itaipu Reservoir (Brazil). Using the data available by Itaipu, from 1999 to 2004, analyzes of multiple regressions were accomplished to determine the relationships of the dependent and independent variables. We applied the trophic state indices (TSI) based on readings Secchi disk, total phosphorus and chlorophyll-a density for obtaining TSI medium. Morfoedaphic index was calculated based on the reading of the concentration of dissolved solids and the inference of fishing yield, from this index. The average results of the trophic state indices indicate an oligotrophic status for the entire reservoir as well as for the riverine, transition and lacustrine zones separately. The fish was yieldn Estimated by the relation with cyanobacteria concentration, and this was the best variable que explained this prediction. The use of the morfoedaphic index (MEI), with the recorded catch data, predictive models can generate que estimate the fishing yield in the Itaipu Reservoir. The relations of MEI with chlorophyll-a and water transparency que Indicate this index may be a good predicting factor for future fish captures.

基于Vine Copula的梯级水库短期发电调度风险估计

基于能准确描述高维变量相关关系的Vine Copula,考虑短期径流预报误差的空间相关性,构建了梯级水库短期发电调度风险估计模型,并将模型应用于长江上游溪洛渡、向家坝和三峡水库,分析了径流预报误差带来的单一水库、梯级水库短期发电调度风险。结果表明:基于C-vine Copula构建的联合分布能较好地描述屏山站、朱沱站、寸滩站和武隆站的日径流预报误差特性;随着水库可调节安全区间范围增大,单一水库发电量不足风险率、弃水风险率均越来越小,梯级水库发电量不足、弃水联合风险率和同现风险率越来越小,即水库调节库容越大,其承担的风险也就越小。

考虑弃水风险的梯级水库中长期多目标优化调度研究

针对现有水电站弃水风险计算结果与实际情况存在较大偏差的问题,基于水量平衡原理,通过识别弃水风险因素,提出了耦合径流和负荷双重不确定性的梯级水库弃水风险量化方法;引入临界弃水概率的概念,提出了基于预警空报率和漏报率联合最小的梯级水库临界弃水概率确定方法以及基于临界弃水概率的梯级水库供水期末库水位消落控制方法;在此基础上,构建了考虑弃水风险的梯级水库中长期多目标优化调度模型,并以乌江梯级水库群为对象开展了实例研究。结果表明:乌江梯级水库群弃水概率与弃水流量间存在显著的单调递增关系;耦合调度期和余留期的两阶段方案发电效益较常规优化调度方案增加了约0.51%,生态效益提高了约1.06倍。

基于谈判博弈的三峡梯级蓄水期多目标调度

汛后蓄水期是三峡梯级防洪向兴利调度转换的重要时间窗口,不合理的蓄水调度将对梯级防洪、发电兴利、生态效益造成不利影响。本文以发电量最大、防洪库容占用比最小以及修正流量偏差最小作为三峡梯级蓄水期调度目标构建优化调度模型,进而引入谈判博弈模型将各个调度目标作为不同谈判主体,通过逐步缩减各调度目标期望效益值进行多轮谈判,最终得到纳什均衡调度方案。实例计算表明,应用谈判博弈模型能够求解得出三峡梯级蓄水期不同调度主体的最优蓄水调度方案,同时该蓄水调度方案也能够达到其他调度主体期望效益值,被其他目标主体所接受。研究成果可为三峡梯级多目标调度决策提供新的思路。

黄河上游近60年水沙变化特征及其影响因素

由于受人类活动及气候变化影响,黄河上游干流水沙特征发生显著变化。为探究黄河上游水沙变化情况,基于黄河上游5个水文站19642019年水沙、遥感影像等数据,利用Mann-Kendall检验法、滑动t检验法、累积距平曲线和双累积曲线等突变检验方法和小波分析法,对黄河上游水沙变化特征进行研究。利用水沙关系曲线及线性回归法等方法估算人类活动和气候对水沙变化的贡献率,并着重讨论梯级水库建设及土地利用变化对水沙的影响。结果表明:1)黄河上游玛曲-小川段流域内降雨量和径流量变化幅度不明显,贵德站、循化站、小川站19862019年年均输沙量分别减至19641985年的9.8%、24.6%、38.8%,输沙量大大减少。黄河上游玛曲-小川段径流量突变多在1986年,输沙量突变多在1969、1986、2004年,径流量存在8、16、22 a周期,输沙量存在4~8、18~21、27 a周期。2)1969年后,河流输沙能力增强,水沙关系显著改变。在不同时段内,人类活动对径流量变化在19872019年贡献率为66.3%,对输沙量变化在19701986、19872004、20052019年的贡献率为72.96%、70.73%、69.7%。人类活动对黄河上游干流水沙影响占据主导因素。3)刘家峡水库淤积最为严重,单库运行期水库淤积量为2.39亿t,排沙比变化范围为1.39%~10.7%。梯级水库联调使得径流量在19642004年间减少47.8%,19642019年间梯级水库减沙94.8%,梯级水库对输沙量影响远大于对径流量的影响。4)19802020年间,草地面积增加了1880.03 km 2,增幅3.1%,有利于减少输沙量,草地拦沙效益大于截流效益。