灞河流域水环境数值模拟研究

Study on numerical simulation of water environment in Ba River basin

【目的】对灞河流域水环境状况进行数值模拟分析,为湖泊型城市河道水质时空分布特征及水质类型主导性指标的分析提供参考。【方法】利用DHI MIKE21FM中的HD模块耦合Ecolab模块,选取溶解氧(DO)、化学需氧量(COD)、叶绿素a(Chl-a)、氨氮(NH_(3)-N)和总磷(TP)共5项指标作为水环境模型的状态变量,参考WQ模板中各指标的生化反应方程并对其修改后,以灞河流域下游城区段内灞河和浐河为研究对象,构建了适用于研究区的水环境模型,利用该水环境模型分析了基准年、丰水年、平水年与枯水年条件下灞河口水质特征,采用BP神经网络算法计算了灞河流域的时均综合水质类型,并对其空间分布进行了分析;采用主成分分析法(PCA)评估了灞河流域时均综合水质类型的主导性指标。【结果】灞河口水质超标因子主要为NH_(3)-N和COD,丰水年与平水年超标时间较基准年有所增加。浐河和灞河交汇前,灞河时均综合水质类型为Ⅱ类,浐河时均综合水质类型为Ⅳ类。浐河和灞河交汇后,灞河时均综合水质类型下降至Ⅳ类。研究区水质类型主导性指标为COD和NH_(3)-N。【结论】灞河流域时均综合水质类型在不同水文条件下基本都处于Ⅳ类。所构建的水环境模型在湖泊型城市河道水质时空分布特征及水质类型主导性指标分析中具有较好的精度和普适性。

【Objective】 The water environment status of Ba River basin was simulated to provide reference for analyzing spatial-temporal distribution of water quality and dominant indexes at urban rivers with lake characteristics.【Method】 After the HD and Ecolab modules from DHI MIKE21 FM were coupled,DO,COD,Chl-a,NH_(3)-N and TP were selected as the state variables and their equations were modified from WQ templates.Ba River and Chan River segments in the downstream urban section of Ba River basin were selected to develop the water environment model that was suitable for the study area.Then,the model was utilized to analyze water quality characteristics at the Bahekou section.The BP neural network algorithm was also introduced to evaluate the time-average comprehensive water quality of Ba River basin and analyze its spatial distribution characteristics.Moreover,the PCA was used to evaluate the dominant indexes of time-average comprehensive water quality at Ba River basin.【Result】 The main excessive indexes for water quality at the Bahekou section were NH_(3)-N and COD,and the standard exceeding period increased in wet and median water years compared with the base year.Before confluence of Ba River and Chan River,the time-average comprehensive water quality in Ba River was grade Ⅱ and that in Chan River was grade Ⅳ.After the confluence,the time-average comprehensive water quality in Ba River decreased to grade Ⅳ.Moreover,the dominant indexes of water quality at study area were COD and NH_(3)-N.【Conclusion】 The time-average comprehensive water quality at Ba River basin was mainly grade Ⅳ at different hydrographic conditions.The developed water environment model held high precision and universality in researching temporal-spatial distribution characteristics of water quality and its dominant indexes for urban river with lake characteristics.