A Comprehensive Analysis Of Roughness Of Gravel Bed Surface

Rough gravel bed surface is widespread in nature,and gravel bed surface roughness is closely related to many problems in river dynamics(such as sediment start,bed resistance,push movement,etc.),but the scientific quantification of the roughness of the bed has been a difficult problem in river dynamics and a challenge that has not yet been effectively addressed.Based on the deep investigation of the natural gravel bed surface,this paper generalizes the classification of the gravel bed surface roughness.Based on the bed surface laser scanning test data,the statistical analysis method and the fractal geometry theory are used to study the roughness of gravel bed surface.Achieved the following main research results:(1)The mean and mode of gravel bed surface elevation is about equal to the average elevation;relative elevation frequency distribution was negative skew,high narrow peak,the negative span area is much larger than the positive value of the span area.(2)The standard deviation of the elevation of the uniform particle bed increases with the increase of the particle size,which can be used as an excellent quantitative index for the roughness of the uniform particle bed.(3)The variation characteristics of the gravel bed surface are the closest to the spherical model,and the spherical model can be used as the optimal model for the analysis of the variability of the gravel bed.(4)The average variation function of the vertical and horizontal profiles of the gravel bed surface is basically the same as the base constant and the block gold constant of the average variation function of the bed surface characteristic direction,but the variation is quite different.(5)The cross-sectional profile and the fractal dimension of the rough bed are related to the median particle size d50 of the bed particles.The upper critical scale can be taken as(0.5-1.5)d50 and(0.8 ~ 2.1)d50,the average width is respectively d50 and 1.5d50.(6)The fractal dimension of the rough bed is related to the position of the datum plane.When the datum plane is covered with the average bed surface,the fractal dimension is real value,and it is sensitive to bed surface change,which can effectively quantify and distinguish the bed surface roughness.(7)The fractal dimension of different direction profile is fairly different and the profile has different degree of anisotropy.The frequency distribution of the fractal dimension of the profile has bimodal characteristics.(8)The larger the particle size of the gravel particles is,the larger the standard deviation of the bed elevation is,the smaller the skewness and the fractal dimension are.(9)Nonuniform gravel particles bed surface gradation composition is the same,the larger the median particle size is,the smaller the fractal dimension is;when the median diameter is the same,the smaller the particle composition is,the larger the fractal dimension is;the larger the bed surface elevation standard deviation,skewness(absolute)and kurtosis are,the smaller the fractal dimension is.(10)The global fractal dimension of the bed surface increases with the increase of the fractal dimension of the profile,and the numerical difference is slightly larger than the local fractal dimension.The variability of the rough bed surface fractal dimension is obviously smaller than the fractal dimension of the profile,and the heterosexual exponential difference is an order of magnitude,Rough bed fractal dimension has good stability,can be used as a rough bed surface characteristics of the integrated quantitative parameters.