Dispersed urban-stormwater control improved stream water quality in a catchment-scale experiment/data and code

Traditional approaches to urban drainage degrade receiving waters. Alternative approaches have potential to protect downstream waters and provide other benefits to cities, including greater water security. Their adoption requires robust demonstration of their feasibility and effectiveness. We conducted a catchment-scale, before-after-control-reference-impact experiment to assess the effect of dispersed stormwater control on stream ecosystems. We used a variant of effective imperviousness (EI), integrating catchment-scale stormwater runoff impact and stormwater control measure (SCM) performance, as the measure of experimental effect. We assessed the response of water quality variables in 6 sites on 2 streams, following SCM implementation in their catchments. We compared changes in those streams over 7 years, as SCM implementation increased, to the 12 preceding years, and over the 19 years in 3 reference and 2 control streams. In an accompanying paper (Walsh et al. in review) we use the code and data stored in this project to demonstrate that SCMs reduced phosphorus and nitrogen concentrations and temperature, and increased electrical conductivity; most strongly in dry weather, with reduced effect sizes following increasingly large rain events. SCM-induced reductions in phosphorus and temperature were of a similar magnitude to increases from urban development, when assessed as a function of change in EI. Nitrogen reductions were observed, even though increased concentrations were not correlated with EI, and are more influenced by septic tank seepage. SCMs had no effect on suspended solids concentrations, which were lower in urban streams than in reference streams.

传统城市排水方法导致接纳水体质量下降。替代方案具有保护下游水体及其他城市利益（如提高水资源安全性）的潜力。其采纳需对其实施的可行性和有效性进行稳健的验证。本研究通过实施一个流域尺度的对照实验，对比了实施前后对溪流生态系统的影响，以评估分散式暴雨径流控制措施的效果。我们采用了一种有效的非渗透性（EI）的变体作为实验效果的衡量指标，该指标整合了流域尺度暴雨径流影响和控制措施（SCM）的性能。我们评估了在两条溪流上的6个监测站点在实施控制措施后水质变量的响应。对比了7年间随着控制措施实施增加而发生的那些溪流的变化，与之前的12年，以及3条参考溪流和2条对照溪流中的19年间的变化。在随附的论文（Walsh等，待发表）中，我们利用本项目存储的代码和数据，展示了SCMs降低了磷和氮的浓度以及温度，并提高了电导率；在干燥天气条件下效果最为显著，而在日益增大的降雨事件中，其效果逐渐减弱。以EI变化为函数评估时，SCMs引起的磷和温度的降低与城市发展带来的增加相当。尽管浓度增加与EI无相关性，但氮的减少更多地受到化粪池渗漏的影响。SCMs对悬浮固体浓度没有影响，城市溪流中的悬浮固体浓度低于参考溪流。