【作者】 张怡辉；

【导师】 沈永明；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2011， 硕士

【摘要】 在河口、海岸水域中存在着复杂的物理过程,内陆径流与外海潮流交汇于此。这两股作用的强弱决定着河口附近的流场特性,若外海潮波强,则流场表现为明显的往复流动,若径流作用更强,则流场以单向的流动为主。长江口作为我国最大的河口,一年四季径流变化比较明显,随着三峡工程于2009年竣工并开始发挥作用,在三峡工程调蓄流量的影响下长江口上游来水量相比较天然情况下有比较明显的变化,这势必对长江口的水流特性产生显著的影响,而流场特性的改变也会给长江口附近海域排放的污水的稀释和输运带来一定的影响。对水环境情况进行分析和评价,进而对其进行有效的规划和管理,对保证社会经济和自然环境的和谐发展具有十分重要的意义。应用水动力模型,对水体的水动力特性进行分析,是水环境分析、评价和预测的重要基础。本论文以2005年11月长江口实测的流速资料为依据,应用ECOMSED模型建立了长江口的三维水动力数学模型,并在此基础上,分析了2010年7月长江流域大洪水期,由于三峡工程调蓄洪水作用,长江口水动力特性的变化以及对上海排放污水的稀释扩散和输运的影响,得出一些规律和认识,具体包括以下几个方面：(1)潮位和流速、流向的对比表明,模式不仅很好的反应了长江口潮位的变化特征,而且也表明该模型用于长江口的流场模拟也是成功的,很好的反应了长江口及杭州湾附近的水动力特性,可以进行长江口及杭州湾附近的水动力数值模拟计算。(2)三峡工程的存在对长江口的水动力产生了一定的影响,对于2010年7月长江大洪水,由于三峡工程的调蓄洪水作用,使得长江口附近的水流流速在落潮时发生明显的减小；涨潮时,流速有变大的迹象。(3)即使是洪水(即大流量来水)对长江口北支的水动力影响也非常小,这与近年来北支萎缩,泥沙严重淤积的实际情况相符合。北支的水动力主要受外海潮波的影响,因此盐水倒灌现象会比较严重。(4)由于三峡工程的蓄水,上游来水量相应减小,使得外海潮波对长江口的影响更加明显,这样就加剧了长江口的盐水倒灌现象,盐水入侵的可能性增加,且时间会更长,对长江口沿岸的生活和生产产生一定的影响。(5)长江口附近的水动力特性,整体呈现表层流速大,底层流速小的特点。三峡工程蓄水与否对长江口的影响,整体上是对表层水动力特性的影响大于对底层的影响。顺着上游来水往长江口方向,三峡工程蓄水与否对表层、中层、底层的水动力特性的影响逐渐减小,而且对表层、中层、底层之间的影响差距也随着逐渐靠近口门而减小。(6)三峡工程的蓄水,使得长江口上游来水量减小,这样就会使长江口附近的上海排出的污水的稀释扩散变得缓慢,且向外海输运的可能性减小,更加容易在近海区域和杭州湾附近滞留,不利于污水的扩散和输移。由此我们可以看出上游来水量对长江口附近的污水的稀释和输运有很大的影响。(7)三峡工程的蓄水使得长江口附近流速发生变化,从而会对长江口附近的泥沙输运和水环境带来一定的影响。长江口作为我国乃至世界比较典型的河口,其水动力的研究对分析和讨论人为影响下的近海水环境变化意义重大。其水动力的影响因素比较复杂,许多过程至今尚未弄清。因此长江口的水动力过程和水环境研究任重而道远,需要更多的学者进行长期不懈的努力。更多还原

【Abstract】 Some complicated physical processes exist in the estuary and coastal areas, where the inland runoff and the sea tides meet with each other. The strength compare of those two flows determines the characteristics of current distribution nearby estuary. When the tides from open sea are stronger, current moves in circles; while the inland runoff predominate, the current just flow mainly towards the open sea. The runoff flows into Yangtze River Estuary (YRE), which is the biggest estuary in China, is totally different in every season. After Three Gorges Project (TGP) has been completed and put into service in 2009, the water volume downstream to YRE varied apparently to the times before because of the water regulation of TGP. So the hydro-dynamic characteristics of YRE changed significantly, which, therefore, would have negative impacts on dilution and transportation of waste water discharged into YRE. To analyze and evaluate the aquatic environment and then making effective manage plans is important for social and natural environment harmonically develop. Analyzing hydrodynamic properties of water body by employing hydrodynamic models is an essential fundamental for water resource analysis, evaluation and estimation.A 3D hydrodynamic mathematical model for YRE was established by using ECOMSED in this paper. The water level and flow rate compared to the observed data collected in No-vember 2005 show that the model is sound. Then, a simulation is conducted to flood season of July 2010 to study the effect of the flood storage of TGP on the hydrodynamic properties and the dilution and transportation of waste water discharged from Shanghai in YRE. Several rules and acknowledgements were obtained as follows:(1) According to the comparison of tidal level and current velocity and direction between simulated and observed data, this mathematical model is not only displaying tidal characteris-tics in YRE, but also showing up the availability of this model working on the simulation of flow field there. It successfully demonstrated the hydrodynamic characteristics around YRE and Hangzhou Bay.(2) Three Gorges Project has a certain impact on the hydrodynamic of Yangtze River Estuary. Take the big flood that happened in July 2010 for example, the flood storage of TGP contributed extremely to decrease flow velocity in ebb tide, while increase in flood tide.(3) In fact, the floods (large volume of flow) do not have much influence on the hydro-dynamic properties of the north branch of YRE, which is because water in the north branch is running off and sludge is silting up badly. The north branch is affected mainly by open sea tidal wave, which brings out a serious problem of salinity intrusion.(4) The flood storage of Three Gorges Reservoir decreases the water volume from up-stream, accelerating the effects on YRE from outside tides, consequently, lifting the possibil-ity of salinity intrusion and giving rise to the period. All those are going to introduce impacts to life and productivity along the river.(5) On the whole, the flow velocity on the surface is high, while that in the deep down is low. Therefore, the effect from impoundment of TGP are mainly on the surface layer rather than on the under layer. Going along with the Yangtze River from upstream to estuary, the influence of the flood storage to the hydrodynamic characteristics keep dropping down from surface layer, to middle layer, and to bottom layer. In addition, the difference between layers is decreasing going along to the estuary.(6) The flood storage of TGP reduces water volume from upstream, slows down the speed of dilution of the waste water discharged near to Shanghai. At the same time, it dimi-nishes the transport possibility to outside sea, which makes it worse for coastal and Hangzhou Bay areas because the waste water just stay around without getting diluted or spread. Hence, we can figure it out how much the upstream water volume impacts on the effluent dilution.(7) The flood storage of TGP changes the current velocity near YRE, which would make effects on the sediment transportation and water environment.As a typical estuary in China, even in the world, YRE plays a non-substituted role in re-searches of hydrodynamic impacts on people living in coastal areas. The influencing elements are complex, even some of which are still in studying. So it needs much more efforts and will be a long and tough work to keep it going.更多还原