天然河道床面糙度特征的试验研究

Experimental Study on Characteristics of Roughness in the Natural River

本文分析了非均匀沙床面形态分布特性 ,得出床面颗粒暴露度和代表粒径的方法难以反映床面糙度的特征 ,为此提出以床面高度函数 Z( x,y,t)的变化为基础 ,根据室内实验的特殊情况 ,以及主要考虑了初始和粗化床面 ,从统计理论的观点分析了床面高度变化均方差 σ,从分形理论的角度考虑了赫斯特数 Hy,分维数 Dy。由于均方差 σ,赫斯特数 Hy或分维数 Dy综合考虑了床面形态对床面糙度的影响 ,因而结合实验资料建立它们与综合糙率曼宁系数 n的相关关系 。

Based on the analysis of stochastic distribution of nonuniform sediment and current methods for quantifying gravel\|bed roughness,the bed elevation field Z(x,y,t) is used as a function of spatial coordinates x and y ,time t .In order to reduce the difficulty for researchers to collect the experimental and field data,this paper only studied the changes and laws of bed elevation field Z(y) of initial and armored beds according to the special property of bed elevation field in the flume.And then,the standard deviation of bed elevation σ ,and the Hurst exponent H\-y and fractal dimension D\-y in the flow direction are obtained by means of statistic theory and fractal theory,respectively.From the analysis of the experimental data,the method of representative diameter has itself limitations,that is,the property of any single particle can not represent that of the whole gravel\|bed roughness,but the standard deviation of bed elevation,Hurst exponent and fractal dimension could express this property because they include the effects of every group\|size particle for the gravel\|bed roughness.Using the experimental data,the correlation between the three parameters σ,H\-y,D\-y and Manning n are established,and their correlation coefficients appear satisfactory.