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.

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。

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。

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。

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。

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。

黄河中下游水资源多目标利益对古贤水库运行的响应

为量化未来古贤水库参与黄河中下游梯级水库群联合运行对供水、发电、调水调沙、生态多目标关键利益及非关键利益的影响,设置2030水平年有古贤水库及无古贤水库两种情景,基于梯级水库群多目标协同优化调度理论构建黄河中下游梯级水库群多目标协同优化调度模型,通过求解模型分析了径流减少及未来综合需水增加的背景下,黄河中下游多目标利益对古贤水库参与联合运行的响应关系。结果表明:与无古贤水库情景相比,有古贤水库情景下水库群调度系统总协同度略微增加,供水与发电子系统有序度有所增加,农业关键期、非关键期多年平均缺水量减少,水库群多年平均发电量增加;除调沙频率略微下降外,有古贤水库情景下输沙、生态目标关键利益及非关键利益均有所提升。

考虑发电与弃水风险的梯级水电站水库风险调度模型

为量化梯级水电站水库调度过程中的风险形势,提出了预报信息驱动的梯级水电站水库风险调度模型。基于长短期记忆(LSTM)神经网络建立风险形势预测模型,通过构造预报入库径流、水库运行工况、调度决策与出力破坏程度和弃水量之间的映射关系,动态推演复杂工况下梯级水电站水库调度风险;建立基于风险形势的梯级水电站水库调度模型,提出发电不足风险预控模式和弃水风险预控模式。选取雅砻江流域下游锦屏一级和二滩水库组成的梯级水电站水库作为实例研究,结果表明:与常规发电量最大模型相比,风险调度模型通过提前降低出力来补偿未来出力破坏时段的发电量,锦屏一级和二滩水电站分别减小出力破坏程度46%、63%,通过提前增加发电流量预留库容来缓解蓄水期后续时段的弃水量,锦屏一级和二滩水电站分别降低弃水流量4.8%、5.4%;风险形势预测模型能够将径流不确定性嵌入风险调度模型中,通过风险预控决策动态响应水电站水库调度运行状态和径流形势变化,在保证梯级发电量的同时有效降低调度风险。

梯级水库下游最不利洪水地区组成法

梯级水库运行调度显著改变了下游洪水的时程分配,而现有洪水地区组成法没有考虑对工程设计和防洪调度最不利或最恶劣的情景。本文基于灾害风险理论,根据未控区间洪量及地区组成概率,提出一种最不利洪水地区组成法。雅砻江梯级水库实例分析表明:最不利地区组成法分配给下游未控区间流域的洪量总是大于同频率组成法和最可能组成法;最不利组成法推求的雅砻江出口断面1 000年一遇设计洪峰、3 d和7 d洪量分别为16 700 m^(3)/s、41.6亿和85.1亿m^(3),均大于其他洪水地区组成法估计值。理论推导和统计试验表明最不利地区组成法可合理分配洪量并兼顾下游防洪风险,具有深入研究和应用的价值。

金沙江下游梯级水电工程库区生态系统服务价值演化及权衡协同关系

基于生态系统服务变化指数、相关分析及空间自相关等方法,对金沙江下游梯级水电工程库区2005—2018年生态系统服务价值进行定量分析,探索库区生态系统服务权衡协同关系的时空演变规律。结果表明:(1)2018年库区生态系统服务价值达到940亿元,研究期间生态系统服务价值总量增加42亿元。(2)库区生态系统服务价值空间分布较为稳定,呈现南高北低格局,空间相关类型均为正相关,生态系统服务价值增益地区集聚于金沙江沿岸。(3)库区生态系统支持服务与供给、调节、文化服务之间表现为权衡关系,供给、调节、文化服务两两之间表现为协同关系,各乡镇生态系统服务的相关关系以协同关系为主。研究结果进一步证明水电工程的实施能改善库区生态系统服务功能,为库区环境保护和土地资源可持续利用提供技术支撑。

考虑生态流量约束的梯级水库分期消落水位多目标优化调度

针对如何表征枯水期季节性特征、优化分期消落水位来指导水库群消落调度的科学问题,提出了考虑生态流量约束的梯级水库分期消落水位多目标优化调度模型。以金沙江中下游6座水库与三峡水库为研究对象,综合运用多种数理统计方法划分流域枯水期;采用逐月滑动计算法推求梯级水库分期消落水位;以生态和发电效益最大为目标函数,利用NSGA-Ⅱ算法求解调度模型,得到不同来水情景下梯级水库枯水期消落调度方案。研究结果表明:不同来水情景下,相较于常规调度方案,选定的优化调度方案可增加梯级水库发电量30.20亿~52.27亿kW·h(增加2.3%~5.0%)和供水量83.15亿~87.14亿m3(增加5.8%~7.4%),并提高河道生态流量保证率2.6%~22.9%。研究成果可为协调梯级水库生态和发电调度提供技术支撑。

东江流域控制性水工程联合调度策略与机制探讨

近年,东江流域旱涝事件并存,防洪与供水安全形势严峻,三大水库和干流梯级电站是东江流域水旱灾害防御中的重要水利工程。收集流域水工程多年运行经验、案例、数据,综述东江流域控制性水工程联合调度在管理体制、防洪调度、水量调度等方面的研究、实践现状,通过数学模型、统计等方法,对现状调度体制与机制中存在的问题进行分析。从管理、技术、研究等角度提出建议与对策。

金沙江梯级库区生态系统服务供需耦合协调度及驱动因素

[目的]探索金沙江梯级水电工程库区生态系统服务供需关系的时空演变规律及其驱动因素,为水电工程库区生态管理提供决策支撑。[方法]基于金沙江梯级水电工程库区土地利用、人口、国内生产总值、归一化植被指数和降水量等数据,采用市场价值法、耦合协调度模型和地理加权回归模型等方法,开展库区生态系统服务供需耦合协调度及其驱动因素研究。[结果]2005—2019年期间库区生态系统服务价值增加了6.8亿元,总量达到了917亿元。生态系统服务供需严重失调和重度失调的区域,主要分布于金沙江北岸的四川省境内,勉强协调和良好协调的区域主要分布于金沙江南岸的云南省境内。植被覆盖对库区生态系统服务供需耦合度呈现正向驱动关系,人口和地形起伏度为负向驱动关系,降水量对库区北部局部地区为正向驱动关系,其余地区为负向驱动关系。[结论]库区生态系统服务供需耦合协调度呈现南高北低的空间分布特征,且受多重因素影响,未来应加强水电工程库区生态系统服务研究。

水库群蓄水调度多目标随机规划与聚类分析

梯级水库群汛后蓄水期蓄水时机、速率、次序决策面临径流不确定、多目标竞合关系复杂等问题。针对蓄水期决策难题,构建发电、蓄满、生态、上、下游防洪安全等指标的水库群多目标随机规划模型,生成非劣解集;采用K均值聚类法提取非劣解集类别特征,分析目标矛盾关系及蓄水机制。以溪洛渡-葛洲坝梯级水库群为例,结果表明:蓄水期来水越枯,蓄水难度越大,综合效益越低,枯水年发电量较丰水年下降了21.6%;上游防洪安全与发电量矛盾性最强,由枯到丰相关系数降低了0.047;溪洛渡、三峡蓄水呈分段式变化,前期快速蓄水,中后期缓速蓄水。本研究提出的耦合水库群多目标随机规划与聚类分析方法对于科学制定水库群蓄水方案具有参考价值。