River Network Structure And Evaluation Of Its Characteristics

The Yongdinghe River Basin is located in the capital vicinity.As the political and cultural center of the country,its situation of water resources security has been paid more attention by academia and the country.River network shoulders the important task of regional development,and as a regional infrastructure,it is of great significance to human life and social development.The structure of river network has a profound impact on the circulation of water resources and regulation function of river network.In this paper,based on the analysis of river network pattern of Yongdinghe River Basin,the water resources accessibility,waterfront accessibility,drainage connectivity and node importance are evaluated and studied.The main research contents and achievements are as follows:(1)Fractal dimension,river network density,channel gradient and curvature were selected to analyze the structure characteristics of river network in Yongdinghe River Basin.It was found that the southwest and northeast of Yongdinghe River Basin developed well,while the northwest and southeast of Yongdinghe River Basin developed poorly,and the relationship between rainfall and river development degree was verified.The river slope in Yongdinghe river basin was between 0~0.55 and river curvature was between 1~3.75.Strahler classification method and Shreve cumulative classification method were used to classify the river level of Yongdinghe River Basin.Based on the classification results of Strahler classification method,the bifurcation ratio and river length ratio of Yongdinghe River Basin were analyzed,and it was found that the development degree of Yongdinghe River Basin was low.(2)There are some spatial differences in the accessibility of water resources in a basin,which cannot be reflected by traditional water resources assessment methods.Based on the Length,Runoff and Viewshed value of each water consumption grid,this paper characterized the corresponding water accessibility with standardized accumulative probability distribution of the three variables.The Copula function was used to connect the accumulative probability distributions of the three variables to construct a joint distribution.Then,the joint probability distribution was used to characterize the water accessibility of all water consumption grids and a grid-scale water accessibility evaluation model-LRV was constructed.This paper chose Yongdinghe River Basin as a case to evaluate the water accessibility by the LRV model.The T Copula function was chosen as the joint distribution function to obtain the water accessibility distribution pattern of the Yongdinghe River Basin.(3)The riverfront accessibility of the Yongdinghe river was calculated by using the potential model.The accessibility of waterfront was evaluated comprehensively by three indexes: population density,accessibility quality of riverfront and resistance cost.According to the characteristics of mountain rivers,the quality evaluation model of riverfront was improved,and the river slope and river shape were added to measure the leisure resources of riverfront.Applying the model to evaluate the accessibility of riverfront in each county of Yongdinghe River Basin,the average accessibility of the riverfront in each county was ranked as follows: Shangyi County,Yangyuan County,Huairen County,Huailai County,Datong County,Xuanhua County,Tianzhen County,Yanggao County,Beijing City,Shanyin County,Ying County,Wei County,Xinghe County,Datong City,Chongli County,Fengzhen City,Huai’an County,Zhuolu County,Shuozhou City.The accessibility of each riverfront was decreasing from the riverfront to the periphery.(4)Structural connectivity and vertical connectivity were selected to characterize the connectivity characteristic of the Yongdinghe River Basin.The structural connectivity of the Yongdinghe River Basin was evaluated by the connectivity analysis method of landscape corridor.The results showed that the river network of Yongdinghe River Basin had a ring degree of-0.25,a node connectivity of-0.50 and a river connectivity of-0.17,indicating that the river network of Yongdinghe River Basin had a poor level of ring formation,connection and connectivity.Based on the current situation of the river barrage,the longitudinal connectivity of the river was evaluated by the barrier coefficient method.The longitudinal connectivity index of the Yongdinghe River Basin was 0.87,and the longitudinal connectivity was poor.Therefore,the overall connectivity of the Yongdinghe River Basin was poor,and its flood prevention function,water allocation function and water self-purification capacity were weak.(5)From the four dimensions of local attribute,propagation attribute,global attribute and network location,this paper selected the degree center,intermediate center,proximity center and improved K-nuclear decomposition,and combined with the analytic hierarchy process,the comprehensive evaluation value of the importance of 111 nodes in the Yongdinghe River Basin was obtained.The importance of the nodes at the edge of the basin was low.The closer the nodes were to the center,the stronger the connectivity was,and the higher the importance was.Most of the nodes with high importance were concentrated in the northeastern of the basin.