中文摘要：

横向混合系数是河流中污染物横向混合特性的重要体现与反映。本文针对不同河道情况下横向混合系数的确定方法进行了分析。首先归纳不同河道的无量纲横向混合系数的量值分布及代表性公式，顺直室内水槽试验的无量纲横向混合系数值在0．1-0．26范围内，天然河道量值分布较为离散，基本大于室内水槽的数值，并对不同代表性公式的适用条件和范围进行阐述；之后总结了利用示踪试验数据计算横向混合系数的各种参数计算方法，矩法和直线图解法简便易操作，线性回归法可分析非惰性污染物，加速遗传算法、人工神经网络等优化算法提高了计算精度并降低了人为主观性；接着详细介绍了弯曲河道中利用横向速度公式带入三重积分来计算横向混合系数的理论方法，Odgaard和Rozovskii的断面横向速度表达式与横向混合系数存在较好的响应关系，量化了二次流对弯曲河道横向混合系数的影响；同时对含植物、有冰层覆盖明渠以及不规则河岸等其他情况下的横向混合系数的探索进行了总结，最后提出了天然河流中横向混合系数研究中有待进一步探讨的问题。

英文摘要：

Based on the rigid water column theory and the pipe system of a practical hydropower station with bifurcation downstream tailrace surge tank, a set of state equations to describe stability of the gover-nor-turbine-hydraulic system under small perturbation is developed. The effect of throttle orifice and charac-teristics of turbine and governor are considered in the model. The stability of the system is analyzed with the application of the state equations and stability theory, which is verified by numerical model of tran- sients based on the Method of Characteristic （MOC）. The influence of sectional area of surge tank and throttle orifice on the stability is also investigated. The results show that the system becomes more stable with the increase of surge tank sectional area and the decrease of throttle orifice sectional area. When the area of surge tank is larger than the stable sectional area, system＇s stability is not sensitive for the in-crease of the surge tank area. However, the stable area of the system decreases obviously as the surge tank area becomes smaller, when the area of surge tank is less than the stable sectional area. The size of throttle orifice can influence the stable sectional area, and the stable sectional area decreases when the ar-ea of throttle orifice become smaller.