【作者】 曹巧丽；

【导师】 刘德富；

【作者基本信息】 三峡大学 ， 水工结构工程， 2010， 硕士

【摘要】 三峡水库蓄水后,库区水位升高、水体流速减缓,库湾和支流污染物的滞留时间延长,水域环境条件发生了显著变化,引起了社会各界的广泛关注。越来越多的学者开始认识到水流变缓是三峡水库支流库湾发生富营养化的主要诱因。一方面水库蓄水使支流库湾流速变缓有利于水华发生;另一方面水库的水位调节以及水库干支流水体物理化学性质存在差异,水库干、支流水体处于频繁的交换状态,这种交换又会反过来进一步改变库湾水体的物理、化学特性,从而不断影响着支流库湾水华的发生。因此,研究清楚三峡水库蓄水后支流库湾水动力特性及其受水库干流影响的特点,是研究库湾水环境状况和解决其水体富营养化问题的基础。本文以三峡水库香溪河库湾为研究对象,利用现场监测数据分析库湾的水动力特性,并以此为基础建立倒灌异重流室内物理模型,模拟在三峡水库典型调度工况下的香溪河库湾倒灌异重流现象,来进一步揭示异重流的水动力学特性,为研究其它支流库湾水动力特性提供理论依据。主要工作及认识如下:1、基于2008年香溪河库湾现场监测数据,对水体流速、水温、密度、水位、温差、流量等因子进行分析,结果表明香溪河库湾在深度上长期具有复杂的分层异向流动特征,库湾底部始终存在流向河口的潜流,大多时候河口处水库干流水体以倒灌异重流的形式进入库湾,2月和3月为底部异重流,4-9月主要为中层异重流,汛后第一阶段蓄水主要为表层异重流,第二阶段蓄水为中层异重流,11、12月分别为底部和中层异重流。香溪河倒灌异重流形成的根本原因是水库干流与支流库湾水体温差和含沙量差引起密度差,其中温差是主导因素。2、以初始水位、入流量、温度差为基本变量,在室内进行了一系列底、中、表温差倒灌异重流实验,通过分析异重流头部移动速度、厚度、交界面高度、潜入点速度等因子的变化过程,得到如下认识:(1)异重流头部移动速度沿程呈线性递减;同一断面处,异重流头部速度随入流量、初始水位及温差的增加而增大。(2)异重流运行过程中,底、表层异重流头部交界面及中层异重流头部下交界面均沿程呈线性升高,同一断面处的交界面高度随入流量及初始水位的增加而升高;中层异重流头部的上交界面高度沿程几乎不变,而同一断面处的高度随初始水位增加而增大。(3)底、中、表层异重流头部厚度均沿程呈线性递减,头部厚度对初始水位变化最敏感,随初始水位升高而增加,而温差变化对其几乎没有影响。(1)异重流运行稳定时前锋过后的异重流交界面形态不变,底部异重流与环境水体交界面比降与水槽底部相反,表层异重流交界面倾向与水槽底部一致,中层异重流上交界面倾向与水槽底部相反,下交界面倾向与水槽底部一致,同时所有交界面比降均小于水槽底坡。(2)室内温差异重流潜入点Fr0 2值分布均较集中,平均值约为0.54;潜入厚度大约是环境水深的0.5倍,稳定后的厚度大约是环境水深的0.4倍。(3)在一定范围内,异重流潜入点速度与入流量、初始水位及温差均呈正相关;潜入点厚度与入流量及初始水位呈正相关,而与温差呈负相关;(4)异重流头部速度与水体密度差及阻力系数呈显著正相关;头部厚度与初始水位及入流量呈显著正相关。(5)实验得到异重流潜入距离的特性与现场得到的基本一致,即与水位、入流量呈显著正相关,与入侵水体和环境水体之间的密度差呈显著负相关。3、对室内、野外温差倒灌异重流的运动特性进行对比分析得到如下规律:更多还原

【Abstract】 After impounding, water environment of the total Three Gorges Reservoir (TGR) has been significantly changed due to dramatically increased water level, lower flow velocity, poorer diffusion ability and longer retention time in the tributaries; these problems have been a matter of social concern. More and more scholars realized that dramatically decreased flow velocity was the key factor driving eutrophication and algal boom problems of the TGR tributaries. Firstly, low flow velocity in tributaries reduced transport ability of the flows and strengthens the biomass H0accumulation directly. Secondly, quite low flow velocity in tributaries prolonged water retention time, enriched nutrients and increased H1light transmittance which indirectly accelerated algal growth. In addition, it is noteworthy that research indicated the tributaries were strongly impacted by reverse intrusion of the TGR arm water with high nitrogen and phosphorus concentration. Therefore, a hydrodynamic characteristic of the tributaries is now a primary goal to study water environment and eutrophication problems of the tributaries.In this paper, Xiangxi Bay (XXB) is chosen as the study area. Based on field data in 2008, the basic hydrodynamic characteristics is analyzed, then a physical model is established to study plunging conditions and motion characteristics of the reverse density currents in XXB. Major works and conclusions are as follows:1. Based on the field data of XXB in 2008, a series of flow velocity, water temperature, density, water level, temperature difference, flow and hydrodynamic parameters were analyzed, the results showed that hydrodynamics of the XXB could be generalized as a bidirectional flow but a one-dimensional flow. The inflow from upstream entered into XXB as a underflow all the time, while the TGR arm water intruded into XXB as reverse density currents most of the time. Underflows occurred in February and March, and then interflows occurred in April to September. Water temperature is the primary contributor to density differences driving reverse density flows, whereas sediment is the secondary in the creation of these flows.2. A series of bottom, mid-depth and surface reserve density current experiments were carried out in laboratory. Initial water level, total inflow and initial temperature difference are the basic variables. Developing processes of the H2correlated hydrodynamic parameters, such as density current front velocity, thickness, height of the front interface, velocity in plunging point are analyzed, the results are as follows: (1) Velocity of density current front during the processes of formation and developing is decreased approximately linearly along H3longitudinal direction; while in the same section it will increase as initial water level, total inflow or initial temperature difference increases;(2) During the propagation process, the height of the front interface of the underflows and overflows will increase linearly and slowly; while in the same section it will increase as the initial water level and total inflow increases; the height of the upper front interface of the interflows are nearly fixed, while in he same section it will increase as initial water level increases.(3) The thickness of density current front decreases linearly along H4longitudinal direction, and more sensitive to the initial water level.3. Comparing the motion of density currents in laboratory with field monitoring results, some conclusions could be obtained:(1) When the reserve density current tends to stable, its interface shape after the highest point is nearly fixed, distribution of interface height of the underflow show opposite tendency with slope gradient of the flume, and the interface slope is lower. Interface height of the overflow is in accord with slope gradient of the flume, similarly, the interface slope is lower.(2) Fr0 2 of the density currents in laboratory are relatively concentrated with an average of about 0.54; the plunging thickness usually occupy half of the entire water depth, and the stable thickness of the density currents decreased to about 0.4 times.(3) To some extent, plunging velocity increases as the initial water level, total inflow and initial temperature difference increases; and density current thickness is positively correlated with the initial water level and total inflow, but negative correlation with the initial temperature difference.(4) Velocity of density current front is negatively related to the density difference and the coefficient of drag, and it is positively related to the initial water level and the total inflow.(5) In general, the hydrodynamic characteristics of the density currents in the experiments are accord with the field monitoring, both show significant positive correlation with the water level and the total flow, and significant negative correlation with the density difference between intruding water and environmental water.更多还原