Research On The Resistance Coefficients And Shaping Parameters Of Complex Mountain Rivers

Rivers are linear natural channels with water flowing frequently or intermittently on the land surface,which are closely related to the birth and development of human civilization.Mountain rivers refer to the rivers originated and located in mountainous regions.The riverbeds of mountain rivers are formed by continuous longitudinal cutting and transverse widening of the water flow,which have large gradient and the longitudinal profile are therefore steep.The cross-sectional shape is mostly V-shaped(canyon section)or U-shaped(widened section)with a small width and depth ratio.The near bank areas and the center of such rivers often rock protruding,and the shoreline and bed surface are very irregular.Therefore,it is difficult to quantitatively describe the flow resistance law of complex channels in mountains,and the key parameters affecting the shaping of rivers are not yet clear.In this study,based on the large-and small-scales field hydraulic experiments conducted in the typical mountain rivers in Taizicheng River Basin,the flow resistance coefficients and key parameters affecting the shaping of river channels were investigated.The main conclusions are as follows:1.The results on the resistance coefficients of large-scale mountain rivers shows that:1)Manning's coefficient n in the upper reaches is larger than that in the middle and lower reaches,and there is no siginifcant difference between n of different tributaries at the intersection location.2)n value and its variation trend are restricted by hydrological period conditions.3)n has good power function relationships with water depth h and Reynolds number Re,a better logarithmic function relationship with Froude number Fr.The ratio n/h and Re is negatively correlated with power function.4)At the significant level of p<0.01,R2,the goodness of fit for n-h,n-Re and n-Fr are all above 0.82,which demonstrated that these relationships can reflect the influence of water flow on n well.2.The results on the resistance coefficients of small-scale typical river reaches shows that:1)In cmparison with the large-scale mountain rivers,the overall variation laws of n in small-scale typical river sections are more stable and significantly related to the characteristics of the river reaches.2)There are positive power functional relationship between n and h.The n-h power functional relationship of typical soil and rock boundary reach has better prediction effects,but such relationship for the gravel complex reach is significantly different which may rely on the complex sturcture of gravel riverbed and its influence on the water flow and flow resistance.3)Power function can well describe the negative correlation between n and Re,and the positive correlation between n and Fr.4)The relationship between n/h and Re can be fitted with a logarithmic function.5)Although there are certain differences between different\river reaches,the relationships of n-h,n-Re and n-Fr are still the best ways to predict the flow resistance coefficients of small-scale typical to reaches in mountain rivers.3.Research on the shaping parameters of large-scale mountain rivers demonstrated that:1)The prediction formula for the bed slope i is a linear function with the independent variables of river bed shear stress ?,cross sectional area A and total flow energy E(R2=0.788,p<0.01).2)The prediction formula for the river width B is a linear function with the independent variables of A,E,hydraulic radius R and critical water depth hc(R2=0.854,p<0.01).3)The prediction formula for h is also a linear function with R,A,? and E as independent variables(R2=0.982,p<0.01).4)A,E and ? are the key parameters determining the channel shaping of large-scale mountain rivers.5)The relationships between Q and h,B and flow velocity v h=0.326Q0.338?B=4.305Q0.207?v=0.683Q0.414 verifies the downstream hydraulic geometric model and determines the main parameters.4.Research on the shaping parameters of small-scale typical river reaches demonstrated that:1)The prediction formula of i is a linear function with ?,n/h and normal water depth hn as independent variables(R2=0.434,p<0.01);2)The prediction formula of B is a linear function with the independent variables of A,Q and unit energy Es(R2=0.903,p<0.01);3)With the independet variables of Fr,Re,E,Q and n,h can be predicted with a linear function(R2=0.861,p<0.01);4)Q is the key parameter determining the channel shaping of small-scale typical reahces;5)The relationships between Q and h,B and v h=0.533Q0.539,B=3.655Q0.287,v=0.512Q0.165 verifies the downstream hydraulic geometric model and determines the main parameters.6)In comparison to the large-scale mountain rivers,the function equations of hydraulic geometrical description for the small-scale typical river reaches has better effects predicting the channel shape parameters.The research on the hydrodynamic characteristics of complex river channels is a frontier field of mordern ecological hydraulics.Based on field experiments,this research systematically studied the resistance coefficients and shaping parameters of complex river channels in mountainous areas,and the research results may provide reference for the construction of ecological treatment engineerings in complex mountain rivers.