| Influenced by natural and human factors in the 1950s,the relationship between Jingjiang and Dongting Lake has undergone major changes.Due to the long-term disrepair of irrigation channels and water conservancy facilities in the embankment area,and the increasingly serious channel siltation,floods and droughts in the Dongting Lake area have occurred frequently,and the water quality has deteriorated.The degree of nutrition is getting worse.Hunan Province plans to implement a series of water system connectivity and natural river improvement projects to cope with increasingly severe water shortages,deteriorating water quality,and floods.This study combines the predecessors’ analysis of the rationality of the water system pattern and connectivity differences in the Dongting Lake planning area,and summarizes relevant documents to establish suitable Dongting Lake water system connectivity engineering standards.Select the graph theory method,numerical simulation method and functional connectivity index to optimize the analysis of typical water system connectivity projects.The main conclusions are as follows:(1)Under optimized conditions,the structural connectivity index of the West-toEast Water Transfer Project in Nanxian County will increase by 1.22%to 3.64%.The flow distribution coefficient at the exit node of the optimized corridor increased by 16.7%,and the water delivery from Songli River to the Zhongjiazui Irrigation Area increased by 13.3%,which can meet the water demand of this irrigation area.The structural connectivity index index of the Huahong Canal connecting project increased by 2.28%to 5.56%,and the water exchange efficiency of the increased storage capacity of the southern and northern lakes in the planned area increased by 55.71%and 12.26%,which is conducive to improving the water quality of the inner lake.(2)The main remediation method of the Dazhong embankment is riverbed dredging.Since there is only one new corridor,the structural connectivity before and after the planning remains basically unchanged,and the overall connectivity is good.Under planning conditions,the connectivity of the river network will increase by 40.0%.The diversion coefficient of the inlet and outlet sections of the river network in the southern area has increased significantly,and the diversion coefficient of the inland river inlet node has increased by 62.5%.The dredging project reduces the flood control pressure of the Weishui River by improving the diversion capacity of the inland river network.The reservoir regulation index of the planning scheme is 0.17.Under the planning conditions,the ratio of water supply and demand has been increased from 0.84 to 1.71,achieving the planning goals of flood control,drainage,and water intake for irrigation.(3)The average flow velocity of the Huangjinzha-Yinjiazhou section under the medium and low inflows decreased by 3.16%and 19.27%respectively from the upstream.The hydrodynamic axis at the entrance of Lake Umeda is close to the left channel,in order to prevent the entrance of Umeda Lake from further erosion and expansion,weakening the diversion capacity of the Nianyuxu River,ecological revetments should be built on both sides of the entrance.The water exchange period of the Nanxian Plain Reservoir under the designed high water level is 22 d respectively.Under the optimized conditions,the hydrological connectivity index of the central and western branches has increased by 15.3%,and the hydrodynamic conditions have been significantly improved.The regulation capacity index of the reservoir under the designed high water level is only 0.10,and the flood control and drainage capacity of the Ouchi River can be exerted by increasing the length of the water storage section,expanding the river channel,and increasing the water storage capacity. |
