基于图论和网络流的河网连通性评价与模拟优化

河网水系连通关乎用水安全保障、水生态文明建设,是当前河湖水域综合整治的重要方面。为此,将河网水系抽象为由节点和边组成的无向图,以河道断面面积作为边权值来表征相邻节点对的过水能力,采用Boykov-Kolmogorov方法计算任意节点对之间的最大流作为两点之间的过水能力,基于河网节点度特征分析疏浚后节点对最大流和节点平均最大流的变化,并以杭州市上城区2016年河道疏浚为例,进行河道疏浚对节点过水能力与河网连通性影响评价。结果表明,河道疏浚后河网水系连通性增加7.89%,最大区域增加40%以上,尤其水系交叉与疏浚密集区域节点过水能力增加更为显著;以该区域为例,采用5种不同疏浚方案对河网连通性增幅及提升效率进行模拟,为疏浚方案的优化提供参考。

Evaluation and Simulation Optimization of River Network Connectivity Using Graph Theory and Network Flow

Water network connectivity plays a pivotal role in water security and ecological civilization construction,which has been viewed as an important aspect for water comprehensive improvement.Using graph theory,the water network can be considered as an undirected graph with multiple interconnected elements which represent rivers by links and junctions by nodes.The weight on edge represents the simplified river cross-section area which can be equivalent to flow capacity.In order to obtain the flow capacity,a maximum flow evaluation scheme between two nodes is designed by using Boykov-Kolmogorov algorithm.By using the maximum flow between nodes before and after dredging based on node degree features,a solution is analyzed for average flow capacity of each node and water network connectivity.The proposed approach has been tested on a river network of the Xiacheng District in Hangzhou with dredging data in year 2016.The result shows that the water network connectivity is improved by 7.89%over the whole area and more than 40%in maximum region after dredging,and significant influenced by intersect density and dredging extent.Meanwhile,five different dredging schemes are used to simulate water network connectivity improvement and dredging efficiency,which provides a reference for scheme optimization.