Relative sustainability assessment of five European projects aiming to reduce rainwater volume in sewer systems
NORIS (No rainwater in sewers) is one of 54 projects financed by the European Regional Development Fund (ERDF) and is conducted as part of the Interreg 111b programme for the countries surrounding the North Sea. Interreg is aimed at local authority service delivery and stimulates transnational cooperation to develop a more balanced and sustainable future for the whole region.
‘Excess’ rainwater in sewer systems creates a range of problems including sewer overflow leading to river pollution, flooding, inefficient wastewater treatment, production of large amounts of sludge and high energy demands in transporting rainwater over large distances. Furthermore, rainwater in sewers means that groundwater is not replenished and can lead to the possibility of dry conditions in one area and surplus water in another. These effects are a problem across the North Sea Region in areas where rainwater, runoff and sewage are collected in the same system, and problems are likely to be exacerbated in future by the effects of climate change and if traditional methods of new development are maintained.
NORIS aims to address these problems in line with the European Water Framework Directive (2000/60/EC) and comprises pilot studies in Sweden, Holland, Germany, Belgium and the UK which attempt in different ways to return the hydrological cycle to a more natural state at a local level by adaptation of the existing sewerage systems. Techniques for reducing the quantity of rainwater in sewers include an innovative bifurcated sewer liner which separates runoff and sanitary waste, an infiltration system designed to fit into street gullies, disconnection of housing runoff from the sewer system and underground storage with controlled release.
The research described here is an overarching work package within NORIS aiming to determine the relative sustainability of the selected local techniques to dealing with excess rainwater. A structured methodology has been developed which engages and empowers the stakeholder community, explores the impacts of the various strategies, demonstrates an integrated sustainability assessment framework and gives user-specific guidance to enable more sustainable choices to be made in future projects.
Each pilot project site has been characterised for a range of criteria describing the existing sewer systems, demographics, economy, governance, environment and political drivers. More detailed data inform baseline sustainability indicators and those for the pilot project solution used, such as the cost of its production in terms of energy as well as financially, its environmental impact and its contribution to social inclusion, via for example, local employment. The pilot projects are being reassessed with stakeholder involvement subsequent to their commissioning. A range of techniques including multi-criteria analysis have been used to analyse the data.
A framework for sustainability assessment is presented that may be adapted to different circumstances within retrofit rainwater disconnection scenarios. It illustrates how decisions have been made, what drivers are behind the decisions and their (positive or negative) contribution to sustainable development. The framework gives all stakeholders access to information regarding the way in which the pilot projects were developed and are being implemented; in this way it also acts as an educational tool, allowing more informed decisions for the future and presents actors with a holistic set of information that would otherwise be disparate and complex to interpret.
A technology seen as a contribution to sustainable development because it alleviates flooding, is inexpensive and causes minimal disruption during construction may have a negative impact on the environment due to its means of production and lack of longevity. The framework allows informed debate on the suitability of trade-offs. The assessment does not give a ‘sustainability value’ for each pilot project, but demonstrates in which ways each is moving towards local sustainable development and means of improvement.
The research illustrates the difficulties faced in urban water of addressing all sustainability principles equally and suggests ways in which these may be better addressed in future projects or in scale-up of the pilot projects. Understanding of knowledge transfer within and between organisations and stakeholders enables identification of the potential for greater transparency and highlights where justification is required in order to better address sustainability principles.
Implementation processes are influenced differently depending upon country, even though the studies are all within the EU. The governance structure and methods of communication and dissemination are varied. Economic drivers are dependent on local politics; environmental concerns take different priorities and technologies can be limited by topography. These issues combined with attitudes to risks and uncertainties within the decision making process makes sustainability assessment a complex and multi-faceted process. A structured framework is essential in order to compare options and inform stakeholders of how decisions are made -which is not only necessary under the auspices of the Water Framework Directive in Europe but is also essential for global sustainable development.