Protecting streams in urban catchments from excess runoff: International examples of stormwater target guidance and implementation

Excess stormwater from cities and suburbs is recognised as the dominant driver of waterway degradation in urban and urbanising catchments, including the loss of aquatic ecosystems and societal values. Global academic evidence makes the case for streamflow targets for waterway protection. The focus for management in these cities and suburbs is moving beyond target pollutant concentrations or loads (e.g., from wastewater or industry) to consider stormwater runoff quantity targets, i.e., addressing excess stormwater impacts. Despite some applications of stormwater targets worldwide, the application is inconsistent, contentious and commonly contested (often during development phases), leaving waterways vulnerable to unabated excess runoff and often irreversible negative impacts. Given global levels of urban development, and loss of freshwater systems, there is an urgent need for flow targets that protect waterway values through guidance to reduce stormwater quantity from urban areas while concurrently increasing groundwater recharge (e.g., to sustain baseflow) and evapotranspiration. This paper is structured to address four questions: (1) What do stormwater targets and guidance look like?, (2) What are the impediments to the development of targets?, (3) What are the impediments to implementation of targets?, and (4) What are the research gaps? With examples from Australia, Germany and the United States, we conclude that there is adequate knowledge and technical understanding, and ultimately stormwater targets must balance completeness of the underlying concepts, social tolerance, and simplicity of application by designers and regulators. The main impediment to the future of healthy waterways in developing and developed urban areas is inadequate policy and political will. Thus, there is an important role for decision makers in this space to shift the current paradigm towards water sensitive cities and a need for clear, enforceable stormwater targets — supported by adequate guidance, governance and capacity — to protect waterways in urban catchments.