三峡水库典型支流库湾不同水团水交换特征的定量标识及其动力学模拟

The water residence time and stratification are the main factors of tributary algal bloom in Three Gorges Reservoir, temporal and spatial distribution of the average residence time in tributary is not considered in traditional computation and simulation. Physical processes of phytoplankton gathering and transporting cannot be explained clearly..The typical tributaries and adjacent trunk streams chosen from Three Gorges Reservoir are studied in this research. Combining stable isotopic tracing methods with three-dimensional dynamic simulation, the characters of different water parcels in the tributary are identified quantitatively. Temporal and spatial distribution of tributary water exchange is analyzed with spatial-based average residence time. Frontal surface, blending and stratification which resulted from the interaction of main stream and tributary are depicted. Influences of the reservoir water storage and discharge on tributary water parcel’s structure and associated effects of nutrients transporting and phytoplankton gathering are clarified. The research result which is an innovation combining stable isotopic tracing methods with three-dimensional dynamic simulation develops a new appreciation for ecological water conservancy and provides scientific supports for overall and accurate solutions to the factors of eutrophication of tributaries.

水体滞留和分层是导致三峡水库支流水华的主要因素，传统的模拟计算未充分考虑到支流水团存留时间的空间异质性，因而不能很好解释驱动支流浮游植物聚散迁移的物理过程。.本项目拟选择三峡库区典型支流及毗邻干流为研究区域，运用稳定同位素水团示踪和三维动态模拟相结合的手段，定量标识支流库湾不同水团性质，以空间分布式的平均存留时间为主要指标，明晰支流水交换周期的时空分布特征，刻画库区干-支流水团交互的锋面、混合、层化过程，阐明工程蓄放调度对支流水团结构以及伴生的营养盐输运、浮游植物分布聚集的影响。课题的成果将通过水团示踪技术与新模拟技术相结合的方案，实现水库生态水利学的新认识，为全面、准确的回答库区支流富营养化的发生机理提供科学支撑。

本项目选择三峡库区的朱衣河、梅溪河、草堂河三条不同类型的支流及毗邻干流为研究区域，运用氢氧稳定同位素和三维数值模拟相结合的手段，对干-支流相互作用的支流库湾水交换过程、水体平均存留时间的时空分布和支流水体平均存留时间对三峡水库调蓄方案的时空响应过程进行了研究。结果表明：三峡水库蓄水后，库区内支流从山区河流转变为河道型水库，其水动力、水交换特性发生了根本性改变。由干-支流水温差造成密度流取代了重力成为了维持支流库湾水体运动的首要驱动力，这也使得支流库湾区别于天然河流和湖泊。在密度流的驱动下，长江干流灌入到支流库湾的水量远大于水位变化引起的水量，使得来自长江的水团成为了支流库湾水体的主要成分。此外，由于在三峡水库调度和密度流的共同作用下，支流库湾水体交换呈现明显的时空变化特征，水体平均存留时间不但在平面上梯度变化不均匀，而且还呈现显著的表底差异，这也与传统的河流和湖泊有明显的差异。三峡水库的水位调度对小型支流和与长江联系密切支流的水体平均存留时间有接近同步的影响，但是对于大型支流水体平均存留时间的影响则存在大约60天的滞后效应。