三峡水库夏季不同支流倒灌特性及其影响分析

为研究三峡库区夏季不同支流库湾倒灌特性及其对水温分层和营养盐分布的作用特性，以及其对水华的影响，于2017年7月对三条不同支流库湾（香溪河、大宁河、小江）的流速、水温、营养盐和叶绿素a等进行了监测。结果表明：夏季三峡库区干流水体主要以中层倒灌潜入支流库湾，均主要为温差异重流，且倒灌潜入深度与厚度主要与支流库湾河口水温分布有关。受干流倒灌的补给作用，三条支流中下游营养盐普遍呈现出“中层>底层>表层”的垂向分布规律，由于上游有磷矿产业，香溪河TP分布情况较其他支流不同，呈现上游至下游逐渐减小的趋势。干、支流间不同的温度差使支流间倒灌异重流的强度存在差异，倒灌异重流将影响支流的水温分层结构，导致支流库湾存在不同水华优势藻种及强度，进而对支流水华产生不同的影响。

Characteristics and effects of different density flows in tributaries of Three Gorges reservoir in summer

Flow velocity, water temperature, nutrients and chlorophyll-a were monitored in the three tributaries (Xiangxi Bay, Daning Bay and Xiaojiang Bay) of the Three Gorges reservoir (TGR) in July 2017 to study the characteristics of density flow and its influence on thermal stratification, nutrients distribution and algal blooms in this reservoir. The results show that bidirectional density currents could be a common flow pattern in these tributaries, and they are primarily caused by the difference in water temperature between the mainstream and tributaries in summer. And the water from the TGR mainstream intrudes into the three tributaries from middle layers, and the backward density currents feature with a depth and thickness mainly related to the water temperature distribution in the tributary estuaries. Under the influence of the mainstream backward flows, nutrients in the middle and lower streams of the three tributaries generally exhibit a vertical distribution structure of “middle layer > bottom layer > surface layer”. Since phosphate rock miners are located upstream of the Xiangxi Bay, its TP concentration presents a tendency of gradual decreasing from upstream to downstream, quite different from the other tributaries. Temperature difference between the mainstream and tributaries varies across the three tributaries, and it results in differences in the intensities of backward flows into the tributaries. The backward flow will play a crucial role in the thermal stratification and the species and intensity of algal blooms in the tributary bays, and then dominate the algal blooms.