The Danjiangkou Reservoir is the water source for the middle route of the South-to-North Water Diversion Project in China. Thus, its water quality status is of great concern. Five water quality indicators （dissolved ...The Danjiangkou Reservoir is the water source for the middle route of the South-to-North Water Diversion Project in China. Thus, its water quality status is of great concern. Five water quality indicators （dissolved oxygen, permanganate index, ammonia nitrogen, total nitrogen, and total phosphorus）, were measured at three monitoring sites （the Danjiangkou Reservoir dam, the Hejiawan and the Jiangbei bridge）, to investigate changing trends, and spatiotemporal characteristics of water quality in the Danjiangkou Reservoir area from January 2006 to May 2012. We then applied a Bayesian statistical method to evaluate the water quality comprehensively. The normal distribution sampling method was used to calculate likelihood, and the entropy weight method was used to determine indicator weights for variables of interest in to the study. The results indicated that concentrations of all five indicators increased during the last six years. In addition, the water quality in the reservoir was worse during the wet season （from May to October）, than during the dry season （from November to April of the next year）. Overall, the probability of the water＇s belonging to quality category of type lI, according to environmental quality standards for surface water in China, was 27.7%-33.7%, larger than that of its belonging to the other four water quality types. The increasing concentrations of nutrients could result in eutrophication of the Danjiangkou Reser- voir. This method reduced the subjectivity that is commonly associated with determining indicator weights and artificial classifications, achieving more reliable results. These results indicate that it is important for the interbasin water diversion project to implement integrated water quality management in the Danjiangkou Reservoir area.展开更多
为提高不确定路网可靠性评估的合理性,设需求服从对数正态分布,假定出行者在随机需求作用下能够达到确定性用户均衡,运用路径算法获得流量,根据BPR(bureau of public roads)型路段特性函数以及对数正态分布的概率特性,给出了路径出行时...为提高不确定路网可靠性评估的合理性,设需求服从对数正态分布,假定出行者在随机需求作用下能够达到确定性用户均衡,运用路径算法获得流量,根据BPR(bureau of public roads)型路段特性函数以及对数正态分布的概率特性,给出了路径出行时间的随机分布,以此为基础建立了路径及OD对出行时间可靠性评估模型.用数值算例验证了评估方法的可行性,分析结果表明该方法能够合理评价需求及其波动程度、路径之间的相关程度对出行时间可靠性的影响.展开更多
基金Acknowledgements This study was supported by the National Science and Technology Support Program （No. 2011BAC12B02）, the National Science Foundation for Innovative Research Group （No. 51121003）, and the Outstanding Doctoral Thesis Fund of Beijing Normal University （No. 105512GK）. We are grateful to the editors and anonymous reviewers＇ careful review of this paper, whom have contributed substantially to improving the paper.
文摘The Danjiangkou Reservoir is the water source for the middle route of the South-to-North Water Diversion Project in China. Thus, its water quality status is of great concern. Five water quality indicators （dissolved oxygen, permanganate index, ammonia nitrogen, total nitrogen, and total phosphorus）, were measured at three monitoring sites （the Danjiangkou Reservoir dam, the Hejiawan and the Jiangbei bridge）, to investigate changing trends, and spatiotemporal characteristics of water quality in the Danjiangkou Reservoir area from January 2006 to May 2012. We then applied a Bayesian statistical method to evaluate the water quality comprehensively. The normal distribution sampling method was used to calculate likelihood, and the entropy weight method was used to determine indicator weights for variables of interest in to the study. The results indicated that concentrations of all five indicators increased during the last six years. In addition, the water quality in the reservoir was worse during the wet season （from May to October）, than during the dry season （from November to April of the next year）. Overall, the probability of the water＇s belonging to quality category of type lI, according to environmental quality standards for surface water in China, was 27.7%-33.7%, larger than that of its belonging to the other four water quality types. The increasing concentrations of nutrients could result in eutrophication of the Danjiangkou Reser- voir. This method reduced the subjectivity that is commonly associated with determining indicator weights and artificial classifications, achieving more reliable results. These results indicate that it is important for the interbasin water diversion project to implement integrated water quality management in the Danjiangkou Reservoir area.
文摘为提高不确定路网可靠性评估的合理性,设需求服从对数正态分布,假定出行者在随机需求作用下能够达到确定性用户均衡,运用路径算法获得流量,根据BPR(bureau of public roads)型路段特性函数以及对数正态分布的概率特性,给出了路径出行时间的随机分布,以此为基础建立了路径及OD对出行时间可靠性评估模型.用数值算例验证了评估方法的可行性,分析结果表明该方法能够合理评价需求及其波动程度、路径之间的相关程度对出行时间可靠性的影响.
