Resilient Urban Water Systems: A Framework for Implementing Green-Gray Infrastructure

Abstract:

Urban water systems have an absolute requirement for infrastructure in order to provide drinking water supply, stormwater management, and wastewater/sewage treatment and disposal. This infrastructure is of two types: traditionally engineered gray, as well as the green infrastructure with which they operate in tandem. This green infrastructure includes terrestrial, aquatic, and wetland environments that provide ecosystem services, as well as the human settlements and governance systems that regulate their use. Urban water systems face increasing challenges to their continued operation from long term structural factors; such as climate change, population growth and migration, evolving technology and associated competing demands for water resource and ecosystem services, and economic cycles that affect the investment in infrastructure services. At the same time, customary short-to-medium-term operational challenges continue; including routine maintenance, regulatory compliance, flooding and drought, and the risk of spills or other potentially catastrophic pollution events. All of this occurs in the context of social equity, in which all users must have access to reliable and adequate services to meet their needs. Resilient Urban Water Systems (ReUWS) must be able to sustain the delivery of services at their designed capacity and planning horizon in the face of these challenges. This study presents a framework for the design of ReUWS, which leverages green infrastructure in upgrading existing gray infrastructure and implementing new hybrid green-gray infrastructure (GGI) to meet the full range of challenges. The ReUWS framework uses concepts, analytical methods and models from the engineering, ecosystem, and social equity domains to integrate technological advancement, eco-hydrological dynamics, and stakeholder participation in the lifecycle of GGI. The current model of the ReUWS framework considers three major urban water resource challenges; sustainable water supply, mitigation of flood threats, and improvement of water quality. We use Baltimore City’s water system as a case study to illustrate how the ReUWS framework can facilitate a participatory approach to implementing GGI that fosters resilience in urban water systems.