EAPSI: Connecting Distributed Impacts in Urban Watersheds to In-stream Hydrology and Water Quality Observations through Refined Landscape Metrics for Optimal Stormwater Handling

雨水通过渗透到径流和不透水表面上的复杂网络在城市流域中流动，这些表面迅速将径流输送到溪流中。事实证明，不透水区域及其由排水管道连接的程度在改变城市溪流的水流动态和水质方面发挥了最大作用，从而导致全世界的情况恶化。这促使人们采用更自然的雨水处理方式，并采用分布在整个城市分水岭的绿色基础设施做法，从源头上处理径流问题。由于城市土地成本很高，因此需要指导，以便更好地选址这些设施，以便最大限度地发挥其有效性，满足当地排水需求，并有助于改善河流状况。该项目将探索城市排水评估的新方法，考虑自然和管道径流路径，并根据不透水表面连通性的衡量标准确定对河流退化有更大贡献的地区。将在墨尔本大学的Tim Fletcher博士和Monash大学的David McCarthy博士的指导下探索方法，使用包括不透水区域及其连通性的已建立的空间数据集进行比较和验证。将使用径流和水质数据集探索不同的流道加权方案，并将重点放在小Stringybark实验分水岭上，以评估与绿色基础设施安装相关的不透水连通性随时间的变化如何与观测到的径流和水质变化相关。城市流域不透水表面的连通性通常被表示为二元连通性，而人们已经认识到，连通性实际上存在于一个连续体上，受风暴特有的特征、先前的湿度条件和可变流动路径断开的影响。该项目将利用代表高程、防渗覆盖和雨水排水网络的高分辨率空间数据来建立相对连通性指数，该指数既提供不透水的横向加权度量，也提供空间上明确的信息，以确定城市分水岭内与河流中的测量更紧密地联系在一起的关键源头区域。Python脚本将采用基于栅格的分水岭表面覆盖和径流流径表示，通过研究径流通过分水岭(陆上、不透水、管道、溪流)的不同流径部分的加权方案来测量连通性。这些加权方案将被校准，以优化将相关景观度量与河流中观测相关联的线性模型的适配性，并将调查流域之间的参数化差异，以评估它们如何有效地代表物理流域特征和径流传输机制。这将有助于验证该方法，并为建立一个可用于未测量流域的工具提供指导，以确定任何城市分水岭内最适合安装绿色基础设施的地区，以减少不渗透的连通性，并通过分布式手段在河流中带来积极的变化。该奖项由东亚和太平洋夏季学院项目资助一名美国研究生的暑期研究，由NSF和澳大利亚科学院联合资助。

Stormwater moves through urban watersheds via a complex network over pervious surfaces that infiltrate runoff and impervious surfaces that quickly move runoff towards streams. Impervious areas and the degree to which they are connected by drainage pipes have been shown to play the greatest role in shifting streamflow dynamics and water quality in urban streams leading to degraded conditions worldwide. This has spurred the adoption of more natural stormwater handling with green infrastructure practices distributed throughout an urban watershed to handle runoff issues at the source. Because urban land costs are high, guidance is needed to better site these installations in order to maximize their effectiveness to meet local drainage needs and contribute to improvements in stream conditions. This project will explore novel methods of urban drainage assessment that account for natural and piped runoff pathways and identify areas that contribute more to stream degradation based on measures of impervious surface connectivity. Methodology will be explored with the guidance of Dr. Tim Fletcher at University of Melbourne and Dr. David McCarthy at Monash University using established spatial datasets that include impervious areas and their connectivity for comparison and validation. Different flowpath weighting schemes will be explored using runoff and water quality datasets and a temporal analysis will focus on the Little Stringybark experimental watershed to assess how changes in impervious connectivity over time associated with green infrastructure installations relate to observed changes in streamflow and water quality. The connectivity of impervious surfaces in urban watersheds has often been represented as binary while it has been acknowledged that connectivity actually exists on a continuum subject to storm-specific characteristics, antecedent moisture conditions, and variable flowpath disconnection. This project will utilize high-resolution spatial data representing elevation, impervious cover, and stormwater drainage networks to establish a relative connectivity index that provides both a landscape-scale weighted metric of imperviousness and spatially explicit information that identifies critical source areas within the urban watershed more closely tied to in-stream measures. Python scripting will employ a grid-based representation of watershed surface cover and runoff flowpaths that will measure connectivity by investigating weighting schema for different portions of the flowpath that runoff takes across the watershed (overland, impervious, piped, in-stream). These weighting schema will be calibrated to optimize the fit of linear models relating the associated landscape metric to in-stream observations, and differences in parameterization between watersheds will be investigated to assess how effectively they represent physical watershed characteristics and runoff transport mechanisms. This will help validate the methodology and provide guidance to establish a tool that can be used on ungauged watersheds to identify areas within any urban watershed that will be best served by green infrastructure installation to decrease impervious connectivity and impart positive changes in-stream through distributed means. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Australian Academy of Science.