The longitudinal dispersion coefficient is a key parameter in water quality model,which has a great influence to the influence area of pollutant.Thus,it has been a research focus in environmental hydraulics.At present,approaches to determine longitudinal dispersion coef-ficient(DL)are mainly based on empirical or semi-empirical formulas without definite physical mechanism. Based on assumption that the bottom resistance was linear with velocity,a power series form for velocity distribution was acquired. By adopting Fischer's integral formula, a semi-analytical method to compute DLwas established and generalized to natural rivers. The applications in more than 100 rivers show that the computed value of DLis about 0.3 to 3 times of the measured value,meeting the requirements of the project. With acceptable accuracy, low computational complexity,the method reflects the dispersion physical mechanism to some extent. Moreover, this formula has the same magnitude error with previous formulas and it means the formula has certain reliability.%纵向离散系数是水质模型的关键参数,对于污染物的影响范围具有决定性影响,一直是环境水力学的研究热点.目前纵向离散系数的确定以经验、半经验方法为主,物理机制不够明确.基于底部阻力局部线性化假定,利用幂级数求解断面流速分布,代入Fischer纵向离散系数积分公式,建立了纵向离散系数的半解析方法.利用100余条天然河流数据进行验证,结果表明计算值为实测值的0.3~3.0倍,精度符合工程要求.该方法推导严密、计算量较小,一定程度上反映了离散的物理机制,与前人计算公式的误差在同一量级,具有一定的可靠性.
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