| 摘要: |
| 支流库湾温差异重流特性是研究其水华生消机理的重要基础。干支流水体温度差引起的密度差导致干流水体在春夏季、秋季、冬季分别通过中层、表层和底层异重流倒灌进入支流库湾。三峡正常运行每年要经历汛前消落期、汛期、汛后蓄水期、枯水期4个阶段，水位最大日变幅可达3.0 m/d。基于经率定验证的香溪河库湾三维水动力水温数学模型，通过对不同水位波动工况进行模拟分析，揭示了库湾温差异重流的变化特性。结果表明：随着水库水位上升，长江干流异重流的倒灌流速和倒灌厚度增大，上游来流异重流的潜入流速减小；随着水库水位下降，长江干流异重流的倒灌流速和倒灌厚度减小，而上游来流异重流的潜入流速增大。水位日升幅增大，长江干流异重流的倒灌距离也随之增大，但增幅较小；水位日降幅增大，长江干流异重流的倒灌距离显著减小，2.0 m/d的水位日降幅使得长江干流倒灌距离减少40%。水位周期性波动会引起库湾水流周期性运动。较高的水位波动频率（每6小时变动1.0 m）使得干支流水体在库湾中下游区域充分混合，降低水力停留时间，有利于限制藻类的生长和聚集。短时间（≤4 d）、小幅度（≤2.0 m/d）的水位波动难以改变库湾稳定的水温分层状态，温跃层平均深度基本不超过5.0 m。 |
| 关键词: 水位日变幅 周期性波动 温度分层 异重流 支流库湾 |
| DOI： |
| 分类号: |
| 基金项目:国家自然科学基金项目(52479062,52309086),山西省基础研究计划项目(202303021212080,202303021212065),山西省水利科学技术研究与推广项目(2023GM22) |
|
| The impact of water level fluctuations in the Three Gorges Reservoir on thermal density flow in the Xiangxi Bay |
|
LANG Yun1, WANG Lingling2, HAN Lijuan1, HU Zijun1
|
|
1.College of Water Science and Engineering,Taiyuan University of Technology;2.College of Water Conservancy and Hydropower Engineering,Hohai University
|
| Abstract: |
| The characteristics of thermal density flow in tributary reservoirs are an important basis for studying the mechanism of algal blooms. The density difference caused by water temperature difference between the mainstream reservoir and the tributary bay leads the mainstream of the Yangtze River flows into the tributary bay through the middle layer, surface layer and bottom layer in spring-summer, autumn and winter, respectively. The normal operation of the Three Gorges Reservoir goes through four stages every year: pre-flood drawdown season, flood season, post-flood storage season and dry season, with a maximum daily water level fluctuation of 3.0 m/d. Based on the calibrated and verified three-dimensional hydrodynamic and water temperature mathematical model of the Xiangxi Bay, different water level fluctuation conditions were simulated to analyze the characteristics of thermal density flow. The results show that with the water level rises, the backflow velocity and backflow thickness of the mainstream of the Yangtze River increase, while the inflow velocity of the upstream decreases. With the water level drops, the backflow velocity and backflow thickness of the mainstream of the Yangtze River decrease, while the inflow velocity of the upstream increases. The greater the daily increase of water level, the greater the backflow distance of the density flow from the mainstream of the Yangtze River. The greater the daily decrease of water level, the much smaller the backflow distance of the density flow from the mainstream of the Yangtze River. The maximum decline of the backflow distance from the mainstream of the Yangtze River is 40 percent with the daily water level decrease of 2.0 m/d. Cyclical water level fluctuation can cause cyclical water flow in tributary reservoirs. A high frequency of water level fluctuations (1.0 m every 6 hours) forces the mainstream reservoir and the tributary bay to be completely mixed in the middle and lower reaches of the tributary bay, which would reduce hydraulic residence time and limit the growth and aggregation of algae. Short-term (≤4 d) and small-amplitude (≤2.0 m/d) water level fluctuations are difficult to change the stable water temperature stratification state of the Xiangxi Bay, and the average depth of the thermocline does not exceed 5.0 m. |
| Key words: water level daily variation cyclical fluctuation temperature stratification density flow tributary reservoirs |
