Research On Geomorphology-based River Network Structure And Fragmentation

The water resources circulation and regulation of the basin are affected by the structure of water network.It is of great significance to analyze the configuration and the structure of water network for the realization of the integrated construction of water network in the basin,the rational allocation of regional water resources and the alleviation of water use crisis.This article studies the quantitative relationship between the geomorphic parameters and the river network structural parameters in Haihe River Basin,and divides the water network hierarchy,evaluates the structural connectivity and longitudinal connectivity of Haihe river network,the importance of river chain connection and node importance of the river network in Haihe River Basin,and puts forward a quantitative description of the cut-off effect of a single water retaining structure and the river network fragmentation and river channal fragmentation based on the distribution of hydraulic engineering projects.The main research contents and achievements are as follows:(1)The river network structural characteristics and geomorphic characteristics of18 representative small mountain basins in Haihe River Basin are analyzed and the correlation analysis method,one-dimensional linear regression,partial correlation analysis and multiple linear regression(stepwise regression)are used to search for the quantitative relationship between geomorphic parameters and river network structure parameters.The analysis results are all tested by significance test,the regression model is finally proposed and the results are reliable.(2)The hierarchical river network of Haihe River Basin is constructed randomly with the stochastic hierarchical tree model and the Bayesian statistical principle,and the maximum likelihood estimation value L(GHS)of the occurrence probability of all the hierarchies is calculated to find the most reasonable hierarchical network,the water network structure of Haihe River Basin is divided into 6 layers,and the number of corresponding layers is 1,6,12,31,84,283,respectively.The river network is divided into four parallel functional levels: agricultural irrigation,urban water supply,flood drainage and comprehensive functional river according to the different functional characteristics of the river channels.(3)Based on the barrier coefficient and the length of the affected river reach,the Cut off Effect Index CEI of the single water retaining structure is proposed to evaluate the cut off effect of the different water retaining structures in the basin.The evaluation results show that the ratio of CEI values of different types of water retaining structures in the interval is significantly exponential distribution,the CEI value of reservoir and hydropower station is generally above and below 1.0,which is higher than that of sluice(above and below 0.4).(4)The Dendritic Connectivity Index proposed by Cote D.et al.is improved by introducing the complete cut-off coefficient Q based on the barrier coefficient of water retaining structures.And a method based on the index is proposed to quantitatively describe the characteristics of river network and river channel fragmentation.According to the calculation results,the following rules can be obtained: the more the number of water retaining structures in the basin,the greater the barrier coefficient is or the more the river section is being cut,the greater the Q and the value of river network fragmentation index RFI is,which means that the river network fragmentation is more serious;the degree of river fragmentation in the plain area of the Haihe River Basin is higher than that in the mountains.The two river basins with great fragmentation are Tuhai Majia River and Heilonggang Yundong,with fragmentation index of 5.54 and4.56 respectively,and Luanhe River basin with the smallest fragmentation index of 1.09.