Re-framing the assessment of sustainable stormwater systems

Sustainability indicators have become popular as a tool for the assessment of sustainable development in different sectors in society, including the urban water sector. For urban water management several sets of indicators have been suggested, using frameworks based on sectors such as drinking water, wastewater and stormwater, or domains such as social, economic and environmental issues. Still, these approaches have some major drawbacks; they have a limited system definition, they are mainly focused on technical systems performance emphasizing a distance to target-perspective, and they focus upon different kinds of impact assessments. This paper presents a different framework for the assessment of sustainable stormwater systems in order to be used in planning and in comparisons between the different available options. It is a re-framing based on systems theory focusing on general systems characteristics instead of a case-specific target to reach. The advantage of this kind of indicator framework is that it relies on the perspective that sustainability cannot be measured on one quantitative scale, that the possibilities of formal comprehensive aggregation are limited, and that a system as such cannot be judged as sustainable without consideration of its surroundings. The indicators presented here can be altered and adjusted to case-specific conditions; they are not as important as the time-and-place-independent framework guiding the assessments