The Impacts Of Hydraulic Projects On River Network And The Function Of Interconnected River System Network In The Southern Three Outlets Of Jingjiang River

Many scholars believe that hydraulic projects is one of the most important reasons for the changing the water system in the lower reaches of rivers.However,at home and abroad it is hard to see the researches who do quantitative researches on the function of interconnected river system network(IRSN),let lone on the River network and the function of IRSN evaluation under the influence of hydraulic projects.In view of this,the main contents of this study take the southern three outlets of Jingjiang River which have more serious engineering water shortage as the research object,based on the original data of water system structure of 1954,1975年,1990,2008 and 2016 extracted by GIS technology,and analyse the characteristics of water system connectivity.Meanwhile,the studies use the correlation analysis,gray relational analysis and set pair analysis to test the influence of the River network and the function of IRSN under the hydraulic projects in the southern three outlets of Jingjiang River.The main results are as follows:(1)Since 1950,in the study area,the number of river,the river frequency and water surface rate have decreased.Besides,the length of river has been shortened.The general characteristics of the River network become more simple.The indexes representing the structural characteristics of the water system have decreased.Drainage density decreased from 0.687km/km2 to 0.475km/km2,and the area length ratio decreased from 3.96km/km2 to 3.17km/km2.what’s more,the development of the river was blocked;The fractal dimension was maintained between 1.5 and 2,and River nets become more and more simple.(2)The hydrological connectivity of regional water systems and the water system connectivity degree a,node connection rate β and water system connectivity y,which represent the connectivity of water systems,also decrease firstly and then increase,and the water system connectivity first decreases and then increases.However,the overall trend is declining.(3)The relationships between the change of structural characteristics of water system and the change of external water conservancy projects are as follows:fractal dimension>water surface rate>river network density>river network development coefficient>river frequency;the gray relationships of the quantity change of internal water conservancy project are as follows:fractal dimension>surface water rate>river network density>river frequency>river network development coefficient;and the correlation degree with total reservoir capacity of the reservoir is:surface rate>fractal dimension>river network density>river network development coefficien t>River frequency.The order of gray relational degree between each index of water conservancy project and that of water system is as follows:total reservoir capacity>number of internal water conservancy projects>number of external water conservancy projects.(4)The number of internal and external hydraulic projects and water system connectivity indicators reached a significant correlate level.Since 1950,with the construction of water conservancy projects,water system connectivity has been changing constantly.From 1950 to 2016,the natural functional level of water system connectivity changed from"excellent" to "poor",from "medium" to "good" and from "good" to"medium".Among them,the main value of the contact of three modules of natural function decreased gradually.The function of flood prevention gradually increased among the three modules of social function,and the function of water resources utilization decreased constantly,and the function of water resources allocation was changed from a low level to a normal level.With more and more construction of hydraulic projects,river network becomes more simple and the function of IRSN is decreasing.However,as long as the natural functions of the river network and the social functions of the water system are fully utilized,and the various water conservancy engineering measures are implemented scientifically,we will be able to improve and solve the problem of water system step by step.