| The river and lake water system is not only an important carrier of water resources,but also an important channel for water circulation.Its pattern plays a key role in the normal functioning of river and lake water ecology,water environment and water security.In the Dongting Lake area,there are natural water channels and artificial ditches intertwined with complex water system patterns.Affected by the evolution of rivers and lakes and human activities,the water system pattern and connectivity have changed greatly.The atrophy of water systems and lake wetlands has intensified,water bodies in the area are not alive,and environmental self-purification capacity is declining.Therefore,it is necessary to study the impact of human activities on the water system pattern and connectivity in the Dongting Lake area.Planning a reasonable water system pattern and connectivity in the lake area is of great significance for the study of the urban river and lake water system pattern and connectivity.This paper takes the Dongting Lake area as the research area,and combs the water system changes and its driving factors in the lake area.At the same time,combined with landscape ecology and hydrology to establish a water system pattern and connectivity evaluation index system,quantitative assessment of the current situation of the lake area and the rationality of the planned water system.An optimization scheme is proposed for the pattern and connectivity of the northern part of the lake area,and the functional connectivity under the optimization of structural connectivity in the Song-li area is analyzed.It also analyzes the reasonable scheduling methods of typical regional water conservancy projects,and provides theoretical basis and technical support for improving the connectivity of rivers and lakes in the Dongting Lake area and implementing water system connectivity projects.The main results of this study are as follows:(1)The results show that there are spatial differences of the water system pattern and connectivity among different areas in the Dongting Lake District.The pattern and connectivity of the current water system in the Tail-stream Area of the Xiangjiang River and Zishui River are at a relatively reasonable level,however the connectivity of the current water system in the Yuan-li District and Song-li District and the Northern area of the Dongting Lake District is unacceptable.The built connectivity index system is not fully applicable to the urban area of Yueyang City.(2)The water system connectivity project(the planning scheme)in Song-li District has improved the water system pattern and connectivity reasonably,but not in the Yuan-li District and Northern region.This shows that blindly increasing artificial channels is not conducive to water system connectivity.(3)After optimization,the three parameters of the optimization scheme increased by 13.2%?6.9%and 4.7%in the Northern region,and compared with the planning scheme,the three parameters of the optimization scheme increased by 26.0%,9.4%and 9.4%in the northern region.The current river channel overflow capacity in Song-li District is F=0.104,and F=0.111 after planning.Its functional connectivity based on the natural and social attributes of the river network increased by 6.7%.(4)The NIKE21 hydrodynamic model was used to simulate the connectivity of rivers and lakes under different diversion conditions of the typical connected project Datong Lake,non-flood period,Bajiao Lake-South Lake flood season and non-flood period.The dimensionless constant C was used to characterize the water connectivity to quantitatively evaluate the connectivity of rivers and lakes.When the diversion flow of Datong Lake is 20 m3/s and the outlet level of Dadong exit is 25.48 m,the connectivity in the non-flood period is optimal;When the initial flow of Bajiao Lake-South Lake diversion was 24 m3/s and the minimum water level of the control of South Lake was 25.86 m,the connectivity during the flood season and non-flood period reached the best state. |
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