影响分汊河道纵向离散的因子权重及相关性研究

Study on Weight and Correlation of Impact Factors of the Longitudinal Dispersion in Braided Rivers

河流纵向离散系数是反映污染物在河流中纵向离散特性的关键性参数。前人研究主要针对顺直和弯曲河道,对于水流结构与边界条件更为复杂的分汊河道研究甚少。本文采用分类回归树(CART)挖掘技术结合示踪试验数据,对分汊河道的不同流速,分流比,宽度比,宽深比及壁面糙度等共108个工况的试验进行分析,研究了各变量因子对于纵向离散系数影响的重要程度,量化了各影响因子的权重大小,其中流速的影响权重最大、其次分流比与宽度比并列,宽深比次之,壁面糙度影响最小;此外,还分析了纵向离散系数与各因子间的响应关系,流速正相关,宽深比负相关,分流比或宽度比等于0.5,即两汊对称情形下离散系数最小。研究成果对于了解与掌握分汊型河道纵向离散特性具有重要意义。

In the natural river, longitudinal dispersion coefficient is a key parameter to reflect the longitudinal dispersion characteristics of pollutants. Previous researches mainly focused on straight and curved channels, however there had little studies on the braided river with complex flow structures and boundary conditions. In this study, a data mining techniques CART combined with tracer test were used to study the factor importance and factor weights. 108 tests were undertaken, considering different flow velocity, diversion ratio, width ratio, width-depth ratio, roughness of side and roughness of bottom. The results showed that, the greatest impact weight was flow velocity, diversion ratio and width ratio tied for second place, then followed by width-depth ratio, and the roughness impact was minimal. The relationship between longitudinal dispersion and impact factors was also analyzed in this article. Velocity was positive correlated with longitudinal dispersion coefficient, while width-depth ratio was negative related with it. When width ratio and diversion ratio were equal to 0. 5 （ namely the two branches were symmetric）, the longitudinal dispersion were minimum. This study results had great significance in the research of the longitudinal dispersion of braided rivers.