Optimization of water system pattern and connectivity in the Dongting Lake area

As the (Yangtze) River-(Dongting) Lake relationship changed and human activities increased,the water system pattern and connectivity in the Dongting Lake area have been also changed a lot,which exacerbated the deterioration of water environment and water ecology. Carrying out the researches on water system patterns and connectivity are important for the comprehensive improvement and ecological restoration of water systems of the Dongting Lake. Based on the network connectivity analysis method in landscape ecology,we created an evaluation index of water system pattern and connectivity including river frequency,river network density,circle degree of water system (α),node connection rate (β),and network connectivity (γ). Here,we analyze the current water system pattern and connectivity of the Dongting Lake Area compared to a planned water system,and we propose an optimized planning scheme for the studied water system. Our results demonstrate that the water system pattern and connectivity of the total area of the Dongting Lake are acceptable,but that there are large differences among sub-areas. The pattern and connectivity of the existing water system in the tail-stream area of the Xiangjiang and Zishui Rivers are at an acceptable level but are poor in the Song and Li Rivers area and the northern region of the Dongting Lake. The planned project will improve the water system connectivity efficiently in the Song-Li Rivers area,but not in the northern region. In the northern region,according to our optimized planning scheme,three indices (α,β,γ) increased by 13.2%,6.9% and 4.7%,respectively,compared to the existing water system,and our optimized planning scheme yielded an improvement of the proposed plan by 26%,9.4%,and 9.4%,respectively.