Study On The Flood Control And Disaster Reduction Based On A Two-Dimensional Numerical Model In Dongting Lake Area

Dongting Lake plays an important buffer role for temporal floodwater detention in the middle and lower reach of Yangtze River region during flood seasons.Moreover,the waterlogging water cannot be drained by itself due to the lake water level is higher than the land area surrounding the lake.Therefore,Dongting Lake area has been facing a severe flood disaster problem.However,serious seasonal water shortage occurs in the lake area in the dry season due to the lack of control measures,especially after the operation of the Three Gorges Project.Hence,how to solve the flooding problem in the lake area,make scientific and efficient use of water resources,and comprehensively reduction of the Dongting Lake has become a hot research topic.Therefore,this paper takes the complex river and lake water network in Dongting Lake area as the research object to investigate the evolution of the lake,the flood control and disaster reduction,and the flooding process in the whole Dongting lake area.Firstly,this paper reveals the change of hydrological regime in Dongting Lake area by analyzing the changes of water level and discharge during the flood and dry periods of "three channels" and "four rivers" as well as the variation of the rainfall in Dongting Lake area based on the hydrological data of Dongting Lake area in the past 60 years.A two-dimensional numerical model including the water and land areas in the Dongting Lake area was built for the first time based on the topographic data of the water and land areas using unstructured grid and the finite volume method.Secondly,the effects of the shrinkage of the lake area on the flood level and discharge in Dongting Lake were quantitatively analyzed by using the two-dimensional numerical model.The results show that the peak discharge and water level increase significantly with the lake shrinkage,and the peak discharge and peak water level occur earlier compared to the natural condition.Therefore,the lake area will face more severe flood disasters if Dongting Lake continues to shrink.Then,the method of the flood control and disaster reduction was investigated.It is found that the lake water level can be significantly reduced by "return land to lake".The flood response varies to the different methods of the restoration of land.The restoration of Gongshuangcha polder has a great influence of the water level in the West Dongting Lake and some parts of the South Dongting Lake,while the restoration of the Qianlianghu and Datonghudong polder has a significant effect on the water level in the entire Dongting Lake.A new flood control and disaster reduction scheme named "River-Lake separation" has been proposed according to the concept of "converting the floodwater to water resources in dry seasons." It is found that the "River-Lake separation" scheme can effectively increase the effective flood control capacity of the Dongting Lake and greatly relieve the flood disaster risk in the Dongting Lake area by discharging the small and medium-sized floods into the Yangtze River without occupying the lake capacity.In addition,it is also found that the seasonal water shortage can be alleviated by using the "River-Lake separation" scheme.Finally,the waterlogging disaster was explored by using a two-dimensional numerical model of Dongting Lake considering the process of rainfall and drainage.The results show that the waterlogging-prone area are the downstream of the "three channels" river-network,Qiangliang polder,Datonghudong polder and the east of Gongshuangcha polder.In general,the drainage capacity of pumping stations is relatively weak due to that most of the reduction ratios of the submerged area in lake area are below 10%.In addition,despite the weak drainage capacity in the lake area,it still has some influence on the flooding process in the lake.