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

雨水通过一个复杂的网络穿过城市流域，这个网络穿过透水表面，渗透到径流中，而不透水表面则迅速将径流转移到溪流中。不透水地区及其由排水管道连接的程度已被证明在改变城市溪流的水流动力学和水质方面发挥了最大的作用，从而导致世界范围内的条件退化。这促使人们采用更自然的雨水处理方式，在整个城市流域采用绿色基础设施实践，从源头处理径流问题。由于城市土地成本高，需要指导更好地选址这些设施，以最大限度地提高其效率，满足当地排水需求，并有助于改善河流条件。该项目将探索城市排水评估的新方法，该方法考虑了自然和管道径流途径，并根据不透水表面连通性的测量确定对河流退化贡献更大的区域。方法将在墨尔本大学的Tim Fletcher博士和莫纳什大学的David McCarthy博士的指导下进行探索，使用已建立的空间数据集，包括不渗透区域及其连通性，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，并将对Little Stringybark实验流域进行时间分析，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与观察到的流量和水质变化之间的关系。城市流域中不透水表面的连通性通常被表示为二元，而人们已经认识到，连通性实际上存在于一个连续体上，受风暴特定特征、先前的湿度条件和可变的流道断开的影响。该项目将利用代表高程、不透水覆盖和雨水排水网络的高分辨率空间数据来建立一个相对的连通性指数，该指数既提供景观尺度的不透水加权度量，也提供空间上明确的信息，以确定城市流域内与河流措施更密切相关的关键水源区域。Python脚本将采用基于网格的流域地表覆盖和径流路径表示，通过调查径流穿过流域的不同部分（陆上、不透水、管道、流内）的径流路径的权重模式来测量连通性。将对这些加权模式进行校准，以优化将相关景观度量与流内观测相关联的线性模型的拟合，并研究流域间参数化的差异，以评估它们如何有效地代表流域物理特征和径流输送机制。这将有助于验证方法，并为建立一种工具提供指导，该工具可用于未测量的流域，以确定任何城市流域内最适合绿色基础设施安装的区域，以减少不透水的连通性，并通过分布式方式在河流中传递积极的变化。该奖项由美国国家科学基金会和澳大利亚科学院共同资助，隶属于东亚和太平洋暑期研究所项目，支持美国研究生进行暑期研究。

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.