Modeling Green Stormwater Infrastructure at the Watershed-Scale in the Salt Lake Valley

Flood infrastructure that uses pipes and culverts, also called gray infrastructure, collects and conveys stormwater to receiving areas, typically oceans, inland lakes, and wetlands. Gray infrastructure increases stormwater runoff volume and exposure to pollutants and prevents infiltration to groundwater. Green infrastructure is increasingly proposed to reestablish ecosystem services that are lost from urban development. This study uses QUAL2Kw to simulate streamflow, stream temperature, dissolved oxygen concentration, and total phosphorus concentration in the Jordan River Watershed in Salt Lake City, UT, USA with and without implementation of grass swales, bioretention cells, and rain gardens at the reach, small watershed, and large watershed scales. Sixty-four model runs simulated streamflow and water quality effects if 10%, 50%, and 100% of the available watershed area converted to green infrastructure. As an example, the 100% implementation of rain gardens for roofs alternative reduced streamflow by 5.6% and 4.6% in the May and June models, respectively. Secondly, the 100% implementation of bioretention cells for parking lots alternative leads to a decrease of 5.8% in total phosphorus load to adjacent surface water bodies. Overall, it takes implementation of green infrastructure on the large watershed scale to see measurable changes downstream. When green infrastructure is implemented on the large watershed scale, total phosphorus concentrations are reduced by 3-6% in reaches that total phosphorus is a pollutant of concern. These findings quantify the potential of green infrastructure to maintain ecosystem services such as water quality improvement, flood mitigation, and water supply.

以管道与暗渠构筑的防洪基础设施，亦被称为灰色基础设施（gray infrastructure），可收集并输送暴雨径流至受纳区域，通常为海洋、内陆湖泊与湿地。灰色基础设施会提升暴雨径流量与污染物暴露风险，同时阻碍雨水下渗补给地下水。为修复城市开发导致丧失的生态系统服务功能，绿色基础设施（green infrastructure）的应用正获得日益广泛的推崇。本研究采用QUAL2Kw模型，对美国犹他州盐湖城境内的约旦河分水岭开展径流、河流水温、溶解氧浓度及总磷浓度模拟，分别设置了未实施与实施草沟、生物滞留池、雨水花园的对比场景，模拟尺度覆盖河段、小流域与大流域三个层级。研究共开展64组模型模拟，分析了将10%、50%及100%的可开发流域面积改造为绿色基础设施时的径流与水质变化效应。以屋顶雨水花园改造方案为例，100%实施该方案可使5月与6月的模拟径流分别降低5.6%与4.6%。其次，针对停车场的100%生物滞留池改造方案，可使邻近地表水体的总磷负荷降低5.8%。总体而言，仅在大流域尺度实施绿色基础设施，方能观测到下游区域的可测变化。当在大流域尺度应用绿色基础设施时，总磷为关注污染物的河段，其总磷浓度可降低3%至6%。本研究结果量化了绿色基础设施在维持水质改善、防洪减灾、水源供给等生态系统服务方面的应用潜力。