Long-term sustainable management of the urban water and wastewater pipe networks
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Water utilities around the world are facing challenges related to the delivery of safe and secure water and environmental friendly collection and handling of wastewater. One of the main components in handling of these tasks is the pipe network for both drinking water and wastewater. It is vital that these networks are managed in a way that will not lead to deterioration of the systems themselves or the quality of the services that they provide. Key challenges going forward are climate change, population growth and urbanization, and increased pressure on the earth’s resources. In the context of public risk management, it is essential that we maintain the quality of the water- and wastewater services. The water- and wastewater infrastructure is considered to be a critical infrastructure delivering services that the public are dependent upon. To achieve this, it is important with a high level of quality in the management of the urban water systems. The literature states that ageing drinking water distribution networks are a threat to water supply in cities and a threat to our well-being. Ageing of the wastewater networks are of great concern to both the sanitation services and possible environmental impacts. The causes for ageing water- and wastewater networks are two-fold: -Lag in rehabilitation compared to the actual needs -Pipes from periods of extensive development and construction (like the post-war period of 1945 to 1965) of pipe networks are nearing their expected service lifetimes Water utilities around the globe have varying degrees of deterioration of pipe networks due to lag in renewal of pipes. The effect of lag in renewal will be further intensified by increased stress from external drivers. Current changes in external drivers and trends are affecting the networks in still unknown ways. One of the drivers associated with future uncertainty is climate change and its effects. There is uncertainty tied to how climate will develop in the future and how the climate change will affect the water- and wastewater infrastructure. Climate change causes a change in the working conditions for the water- and wastewater systems and is expected to influence the deterioration processes of pipes. For wastewater, the main impact will be due to increased intensity of precipitation events and runoff. Changed temperature patterns during winter will impact the failure rates of both water- and wastewater pipes in positive ways. This study has focused on long-term management of the urban pipe systems and the issue of sustainable decisions and implementations. One paper looked at the possibility of calibrating survival functions used in long-term rehabilitation modelling, in order to improve the accuracy of long-term rehabilitation and investment planning. The result of this work was a calibration process applied to groups of pipes (referred to as cohorts). This process was later implemented in a calibration tool developed through a master thesis (Okstad, 2017). Another paper looked at the issue of planning for an uncertain future. Futures research was central in this work, and the multiple scenario planning approach was reviewed and implemented in a Norwegian case study in order to show the approach applied to a water utility. The work was approached from a broad perspective, emphasizing both the quantitative and the qualitative analyses approaches. This work then crossed into several smaller sub case studies focusing on specific details of the larger study. The main objective of the work was to establish a process of future visioning for the water community, and at the same time analyze the future impact of some external drivers through quantitative modelling. For the third paper we looked at the long-term sustainability of rehabilitation strategies, focusing on different combinations of replacement and no-dig methods. Current practice and understanding is that no-dig methods have considerable lower cost and considerable less environmental impact than replacement technologies. This hypothesis is further tested in the paper, where a life cycle approach for rehabilitation technologies is presented. The life cycle approach is based on the survival function for rehabilitation methods. The work also shows how different combinations of rehabilitation approaches can be analyzed. The main advantage of this approach is that rehabilitation approaches can be compared on equal grounds, where actual expected service life of the pipes, and the variation of the service lives, are taken into consideration. The fourth paper dealt with one of the mentioned sub case studies. This paper looked at the expected future impact of increased temperature on the failure rate of drinking water pipes in cold climate regions. The conclusion to the paper was that the increased temperature has a positive impact on failure rates, ranging from a 2.7 to 7.2 reduction in failure rates (depending on climate scenario) until 2070. These results can be used when assessing future rehabilitation needs. The thesis ties all the papers together into a common thread. The purpose is to equip water engineers, and thereby water utilities, in planning for a sustainable urban water system for the future.