【作者】 黄颖；

【导师】 李义天；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2005， 博士

【摘要】 流域内人口密度高,河流是人类赖以生存的环境的重要组成部分,兴建水库引起的河床调整必然将对流域社会、经济产生深远影响,对工程效益以至成败的影响也是显而易见的。一方面,为了开发利用水资源而兴修水库等工程是非常必要的,这将不可避免地引起水沙变异;另一方面,为了保障下游两岸的安全和稳定,又需要避免河床形态调整带来的负面影响。因此,需要了解河流在自然状态下,以及受到干扰后的调整过程,从而能够使人类整治行为更好地顺应河流的调整趋势。然而,当前针对具体河段的河床演变以及整治措施比较多,对水库下游河床调整的机理研究较少,相应的整治和防护措施研究则更加贫乏。 本文以水库修建后水沙变化为主线,将水库下游的河道整治与河床演变相结合,同时注重了水库下游纵向、横向河床变形的发生发展规律,以及新环境下河道整治、防护措施所面临问题,提出初步的改进和解决方法。 取得主要研究进展如下: (1)分析水沙变异下河床演变特性及整治所面临的挑战,提出河床整治以河床演变为基础,当水沙变异后河床演变呈现出新的特征,这必然也将对河床整治提出新的要求。 (2)通过国内外多个水库下游实测资料的系统分析,对水沙输移的一般特性进行了总结,得出以下认识:水沙条件发生较大变化时,河床调整十分迅速,并且调整随时间的发展是非线性的。在最初的时刻强度最大,逐渐减缓直至达到新的平衡。水库下游河床演变现象,主要表现在纵断面和横断面变化上,随着水沙条件变化的幅度,河床形态的调整速率也具有阶段性。基于以上特性,结合丹江口水库建库前后下游演变情况,将本文总结的规律和实际的河床演变现象进行了对比检验,表明本文得出的认识对实践具有一定指导意义。 (3)对电站日调节波的变化特性进行了分析,指出日调节波对河床演变的影响随着水库调节方式以及河道特性的差异而不同。结合三峡电站日调节资料,对日调节波进行模拟分析,结果显示日调节波将加剧局部比降对航运的负面影响。 (4)总结了河床纵向变形的一般特性,并对水沙变异后河床纵向变形特性进行了分析;比较了预测水沙变异后河床纵向变形深度的估算方法,并以三峡下游沙卵石河床为例,利用数值模拟方法估算了河床的纵向冲刷发展过程。然后结合河床纵向演变特点,对各种纵向防护措施效果、适用性、型式以及稳定性进行了探讨分析,并指出了改进现有防护建筑物的必要性和途径。建库后,由于沿程河床冲深,将使建筑物附近出现新的冲刷,即所谓的断层冲刷问题,因此,一方面要正确估计天然情况下各种防护措施附近的最大冲刷深度,另一方面要对水库修建后可能出现的断层冲刷进行防护。为此,本文对估算建筑物附近最大冲刷深度的方法进行了比较分析,利用实测资料,改进了现有一些冲深估算公式。更多还原

【Abstract】 With dense population in basin, rivers are important components of environment. When reservoirs are built on rivers for certain purposes, downstream channel adjustment will be apparent, which will inevitably affect the sustainable development of society and economic in watershed scale. Negative impact aroused by these projects even will overtake their benefits. Thus, on the one hand water resource exploitation are necessary for energy deficit, which will consequently alter water and sediment delivery to downstream reach, on the other hand human have tried to harness the power of channel and create more stable system to protect surrounding communities. So, it’s not only important to understand the natural variability and dynamics of river system, but also crucial to have the ability to predict its adjustment under disturbance. Base on greater understanding of river processes, human can create the beat possible scenario of river management and promote successful controlling measures. To nowadays, related researches are most aimed in some local river reaches, orienting at natural evolution process. Few of previous researches are about the mechanism of riverbed adjustment downstream dams, and few about corresponding harness works.In this paper, researches are focused on channel responses under altered water and sediment regime downstream dams, based on which the associated protection measures are also presented. Several key problems are emphasized, including the longitudinal and lateral adjustment process, stabilization of protection works under post-dam environment. Primary improvement and solution of river system harness are put forward.Some main improvements are described as following:(1) Analysis about the new characteristics of channel dynamics and the challenges on river harness in new environment. It is point out the good understanding of channel evolution is basis of river control works, when flow and sediment regime change.(2) Based on systematically analysis about the worldwide survey data of several reservoirs, the general features of water and sediment transportation is summarized. Some key conclusion listed below: Channel response rapidly to disturbances on flow regime and sediment amount, the change process shows nonlinear trend. The magnitude of adjustment is most strong at the beginning, and then it decreases gradually till it adjusts to a new balance. At downstream reaches, the phenomenon of the channel evolvement consists of longitudinal and lateral adjustment. With the change extent of water and sediment, the form of channel adjusts periodically. Based on these laws, the channel evolvement downstream Danjiangkou reservoir is analyzed and compared. It can be seen that the conclusion of this paper can give some guidance in practice.(3) According to the variation analysis of power station daily regulation wave (DRW), it is found that the DRW have different effect on the riverbed evolution with the difference of reservoir regulation modes and channel characteristics. Based on the daily regulation data of Three Gorge station, the process of DRW is simulated and analyzed and the result show that the DRW aggravate the negative effect of local gradient on navigation.(4) In this paper, the character of riverbed longitudinal deformation (RLD) isconcluded and the change character of RLD with flow and sediment regime variation is analyzed. Based on the comparison of evaluation approaches which predict the depth of RLD with flow and sediment regime variation, taking example for the sand-pebble riverbed downstream Three Gorge Dam, the process of the riverbed longitudinal erosion is simulated by using the numerical simulation. Then, according to the character of the riverbed longitudinal deformation, the effect, applicability, form and stability of different longitudinal protective measures are discussed and analyzed. It is found that the accurate estimation of maximal erosion depth around protective engineering and consolidating the dislocation which is caused by riverbed further erosion post-dam is the base of protective engineering improvement. In the paper, the different evaluation approaches of maximal erosion depth around protective engineering are compared and some formulas are improved based on the field data.(5) In general, the characteristics of lateral adjustment of channel are summarized. At the same time, the mechanism about the channel responses in condition of variance of water and sediment is analyzed. Then we get conclusions like these: channel adjustments downstream the dam is complicate. The first reason is because of the variance of the streamwise water and sediment condition. Second is on account of the variance of the capability of riversides and riverbed to resist erosion with time. Near the dam, the discharge becomes even and fewer, as well the quantity of sediment reduction. At the same time, little far from the dam, quantity of sediment recovered and increases gradually. Because riverbed becomes coarser, the length in which sediment can recover becomes far and far from the dam. Of course that will make the capability of riverbed stronger and the capability of bank weaker. All these factors may bring on diverse phenomenon when bank and riverbed adjust. So, when understanding and estimating the metamorphose of the downstream reach of reservoir, these dynamic features are needed to take care. From viewpoint of large spatial and temporal scale, the lateral activity of the channel has weakened and the river width is narrowed. But, for quite long time, the under-saturation has caused erosion, during which process, the under saturation has taken place of the discharge reduction to become the main factor. For that reason, at sections where bank resistance is weak, river widen is apparent.(6) Local distortion-bankfailure is analyzed. It is concluded that in post-dam period the intension of bankfailure is weakened because of flow process flattened, but its scope will increase. The point of curvature will shift downstream, and bankfailure will happen because of bed scouring. Then, according to the character of the riverbed lateral deformation, the effect, applicability, form and stability of different lateral protective measures are discussed and analyzed. It is found that the accurate estimation of maximal erosion depth around protective engineering and consolidating the dislocation which is caused by riverbed further erosion post-dam is the base of protective engineering improvement. It can use jackstone in advance and increasing roughness to strengthen the stability of engineering measures.(7) Conclusion of the characteristics of riverbed evolution of downstream of the Yangtze River in natural condition is used to estimate the channel response after TGP built. Every reach will appear different adjustment tendency because of the differences of boundary condition, river channel pattern and riverbed scouring process of thedownstream of dam. Based on these theoretical analyses, the engineering measures and its planned layout in downstream of Changjiang River are studied. Takeing Zhoutian Reach as an example, primary advice is put forward for practice.(8) Aimed at reducing the new phenomena such as bed degradation and water level decrement after dam building, a new work is introduced by improvement of existing engineering measures. The new work not only increase roughness of channel bed, but also protect riverbed from erosion to achieve the propose of maintaining water depth. The effectiveness of this measure is closely related to the diameter of the roughness material to be used. The stability of material, increase of water depth, variations of hydraulic gradient and velocity distribution in navigation channel after increasing of roughness must be comprehensively studied to prevent from harmful influences to navigation. This engineering measure is applied to solve the problem of insufficient water depth of navigation channel probably when the Three Gorges Project is put into operation. Through analyzing its theory and numerical simulation, the place, time, effect and the influence of daily-regulation wave of the engineering measure are capered, it concludes that increasing roughness can be used to maintain or lift Yichang’s water level.更多还原