中文摘要：

从掺混长度理论的基本假定入手，分析菲克定律解释紊动扩散现象的局限性，根据有限掺混长度概念，对明渠流中悬沙浓度垂线分布进行研究：由垂向紊动强度确定掺混速度，分析水体和泥沙作为不同研究对象时掺混长度的差异，定义水体掺混长度和泥沙掺混长度概念，依据卡门紊流相似假说和水流剪切应力分布特征，确定泥沙掺混长度的垂线分布，考虑浓度对泥沙沉降速度的抑制作用，建立明渠流中悬沙浓度垂线分布模型，并进一步分析浓度和颗粒大小对泥沙掺混长度的影响。计算值和测量值的比较表明，该浓度分布模型能够较好地反映明渠流中悬沙浓度垂线分布特征。

英文摘要：

According to the mixing length theory, the limitation of Fick＇s law for diffusion is analyzed and a model for vertical suspended sediment concentration is derived based on the new conception of finite mixing length. The mixing lengths for water and sediment are defined respectively, which are derived through Karman＇ s similarity theory and shear stress distribution in open channel flow; the mixing velocity is determined from turbulence intensity in the vertical direction; the hindered effect of concentration on settling velocity is also considered; at last a model for vertical suspended sediment concentration in open channel flow was developed. Using the model, the effects of concentration and sediment grain size on mixing length are analyzed. Comparisons between the calculated results and the measurements indicate that the results of the model agree well with the experiments.