The Evolution Of The System Of Dongting Lake And Lake Environment And Its Driving Factors

Dongting Lake is the most important key position for adjusting water flood and sedimentation of the middle reaches Yangtze River. The area of Dongting Lake was 6000km2 in Qing dynasty when it reached the largest .After that time, the area of Dongting lake reducing the scope continually. In 1980,the area of Dongting lake was only 2691km2。As the water area has declined, in the lake region flooding and waterlogging disaster are continually aggravating, and ecological environment is worsening comprehensive. These troubles threaten the security of this region seriously. Therefore to study Dongting lake's evolution and development situation, explore the correct understanding method and thought about Dongting lake's question become urgent matter.A quantity of research achievement about the Dongting lake environment development have gained by formers,relating to hydrology,history,geography,climate,weather,and these conclusion are very important.On the basis of the comprehensive review of the study achievements for this problem, new breakthrough of thought is making every effort to gain in this thesis, avoiding the limitations of separated research process of different subject and studying by a multidisciplinary connection and infiltration way. Taking the Dongting Lake as the core, vision excessively expansion is avoided. The effect to the lake evolution of movement of flow and sediment, geological activities and human activities in Dongting Lake area is thinking in its entirety and systematically analyzed. The Dongting Lake is taken as the key point of research and meaning while it can be viewed a continuous developing environment system. The evolution law in history period and modern times is analyzed, and the affect of every driving factors,influence factors and lake's reaction is investigated.Based on systems engineering theory, taking the Dongting Lake as the research target, the theory frame of Lake Environment system analyze is build in this thesis.With time and space dimension of engineering application, the driving factors,influence factors and characteristic of Dongting lake's evolution are discussed. The law of origin and evolution in nature circumstances and their resulting changes of structure function and mechanism caused by human activities are explored. The space-time feature of the runoff and sediment compose, erode and deposit, bed evolution in modern times Dongting lake is summarized;the development of topographic feature and its period was discussed. The geological background, formation cause and history evolution of the environment system are reviewed. The evolution characteristic of modern times'Dongting Lake is laid stress on. The geographic information system(GIS)and remote sensing(RS) and other means are applied for analysis,comparison and confirmation. Taking some particular region and appearance as example, proceed from different driving factors,many related factors influence to evolution are analyzed, affect of every factors are revealed respectively.The distribution characteristic of incoming condition of flow and sediment, sedimentation and evolution of modern Dongting Lake is affected by many factors,taking these factors as internal cause and external cause tow kinds here,the development topographic feature and its phase of Dongting Lake are discussed,the critical threshold value is proposed.The existence of vegetation influences the evolution of lake significantly. For understanding this influence ,the resistance to flow by vegetation should be firstly research. From the basic principles of hydrodynamics point of view,the resistance distribution characteristic of open channel bed with vegetation was analyzed,and the influence on bed resistance of the vegetation height inhomogeneous was investigated further。Taking Muping Lake as an example, 1:10000 topography maps are employed. The DEM (digital elevation model) of 1975 and 1995 is built. By GIS the relationship between evolvement of scour and sedimentation and distributing of the vegetation is discussed. By GIS treating,the quantity and space regulation of the change of sediment deposition and erosion are discovered consequently. Combined 11V1VVGIS with RS, the effect of mud deposition to vegetation distribution and also the quantity effect of the growth of different vegetation to mud deposition are analyzed. The results reveal the evidence that mud deposit is closely related to vegetation distribution. The features of mud deposit determine the relation change of different types of vegetation. Mud deposit continually, the area of water region would decrease, the area of continent would expansion, and the vegetation on continent would adjust. The features of mud deposit in continent in different elevation determine the relative rate of extension of different vegetation. No uniformity of mud deposit in space would lead to regional difference of vegetation distribution and change. The superiority vegetation of the regional is bent on which mud deposit faster. Because the features of various vegetations are difference, the mud deposit situation in different vegetation regional is not the same.RS and geology analytical method is applied to investigate on geologic origin and evolution of bed falling-step. It is known that the geological background is the basis of lake bed evolution,the geological background forms the border for water flow, mud movement and human activity. For modern times lake bed evolution,modern geological transition is one of the major driving factors, but not the only prime control factor. The sedimentation thickness, mutation of the lithologic character, and the structural unit distribution are the important influencing factor which causes the original bed river falling-step formation. The control factor of the original bed river falling-step formation in Xiangshuikan reach in Caowei River is geological transition. The phenomenon forecasting based on RS and geology analytical method is confirmation by topography map there.