Evaluation of a Hybrid Green/Grey Approach to Address Neighborhood Flooding and Other Watershed Issues: Closure from a Texas Case Study

摘要

As introduced at the 2014 EWRI Congress, the City of Austin undertook a rigorous planning and modeling study to evaluate decentralized, green infrastructure approaches for neighborhood flooding and other watershed management issues. This study, which was recently completed, provided rare opportunities to perform model calibration of a small urban watershed, conduct detailed two-dimensional modeling of overland flow, and evaluate various potential control alternatives. The goal of this study was to evaluate whether alternative flood control approaches, based on decentralized controls, could be more cost-effectively implemented than traditional approaches while providing additional benefits such as reduction in pollutant loads and channel erosion, increase in water supply, and neighborhood improvements. More recently, additional model iterations were completed and the monitoring record was expanded to include major rainfall events. The study concluded with development and evaluation of a preferred green/grey hybrid option and associated implementation guidance. The preferred approach involves a combination of green infrastructure retrofits for hydrologic source control (implemented through public projects and private property incentives) combined with strategic traditional drainage improvements to address capacity limitations. The combination of elements allowed the frequency of critical flooding to be reduced within the watershed by 5 to 10 fold and structure flooding to be nearly eliminated up to the 25 year peak event, while maintaining no increase in peak flow at the watershed outlet. This has significant cost savings compared to the traditional approach, as it avoids the need for a series of upgrades to the downstream conveyance system. This paper provides a summary of final study findings and highlight the findings that are applicable to other municipalities, land developers, and stormwater professionals.