西安市城市主干道路面径流初期冲刷效应

以西安市城市主干道南二环太白路高架桥为路面径流采样区域,采用人工等时间间隔采样方法,在桥梁排水立管对2010年9—11月的3场径流事件进行全程采样,测试径流过程SS、COD、溶解性COD、NH3-N、Pb、溶解性Pb、Zn和溶解性Zn的浓度变化,研究路面径流的初期冲刷效应及其影响因素。结果表明,西安市城市主干道路面径流污染严重,降雨数小时后的末期径流仍具有较高的污染水平;径流过程污染物浓度变化规律与其赋存形态有关,SS、COD、Pb等以颗粒态为主的污染物的浓度随雨强变化剧烈波动,NH3-N、溶解态COD、溶解态Zn等以溶解态为主的污染物浓度变化受雨强影响较小,随径流过程呈逐渐减小趋势;路面径流初期冲刷现象并非普遍存在,与污染物的赋存状态和场次降雨特征密切相关,溶解态污染物易于出现初期冲刷现象,颗粒态污染物是否出现初期冲刷与场次降雨特征有关;测试的3场径流事件初期30%的径流携带的SS、COD、溶解性COD、NH3-N、Pb、Zn和溶解性Zn的负荷占场次径流总负荷的比例分别为21.8%～50.0%、25.5%～49.3%、36.3%～52.6%、52.6%～66.7%、26.8%～45.0%、27.2%～63.4%和36.2%～62.6%,表明仅对初期径流进行治理无法实现对西安市路面径流污染的有效控制。

First flush effect of urban trunk road runoff in Xi＇an

Urban trunk road runoff caused by three rainfall events were sampled by labor with equal interval of time during the rainfall process at south second ring road in Xi’an from Sep.to Nov.2010.Concentration variations of SS,COD,dissolved COD,NH3-N,Pb,dissolved Pb,Zn and dissolved Zn were tested during runoff processes.The first flush effect and the influencing factors of road runoff were investigated.The result shows that urban trunk road runoff of Xi’an is seriously polluted and the final part runoff still has a high pollution level.The rule of runoff concentration variation is related with the mode of occurrence of pollutants.The concentrations of granular state pollutants,such as SS,COD and Pb,are mainly influenced by rainfall intensity during runoff process,while concentrations of soluble pollutants,such as NH3-N,dissolved COD,dissolved Zn,are gradually reduced during runoff process and are not influenced by rainfall intensity seriously.First flush phenomena of road runoff are not common,which is influenced by the mode of occurrence of pollutants and rainfall characteristics.Dissolved contaminants in runoff are prone to first flush phenomena,while first flush effect of granular state pollutants are seriously influenced by rainfall characteristics.The load ratios of SS,COD,dissolved COD,NH3-N,Pb,Zn,and dissolved Zn of initial 30% runoff volume to that of total runoff volume are 21.8%~50.0%,25.5%~49.3%,36.3%~52.6%,52.6%~66.7%,26.8%~45.0%,27.2%~63.4% and 36.2%~62.6%,respectively.Thereby,it can be concluded that only initial runoff treatment will not realize the pollution control of urban road runoff successfully in Xi’an.