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Resilience of Water Supply Systems in Meeting the Challenges Posed by Climate Change and Population Growth

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Resilience of Water Supply Systems in Meeting the Challenges Posed by Climate Change and Population Growth RESILIENCE OF WATER SUPPLY SYSTEMS IN MEETING THE CHALLENGES POSED BY CLIMATE CHANGE AND POPULATION GROWTH Pradeep Amarasinghe BSc.Engineering (Civil) MEng. (Water Management) A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIRMENTS OF THE DEGREE OF DOCTOR OF PHILOSOPHY SCIENCE AND ENGINEERING FACULTY QUEENSLAND UNIVERSITY OF TECHNOLOGY 2014 Keywords Resilience, Potable water supply, Meta-system, Climate change, Population growth, System Dynamics modeling, Indicators ii Abstract This research study focused on an investigation of resilience of water supply systems to climate change and population growth impacts. A water supply system is a complex system which encompasses a diverse set of subsystems which lie on socio- ecological and technical domains. The interrelationships among these subsystems dictate the characteristics of the overall water supply system. Climate change and population growth are two issues that create qualitative and quantitative impacts on surface water resources that influence the functions of a water supply system. Due to the complexity of a water supply system and the dependability of water on climate conditions, provision of a reliable potable water supply is a challenge. Therefore, effective management of water supply is a key pre-requisite. For achieving management goals in complex systems, complex procedures may be required. Depending on uncertain climatic conditions, one approach to satisfy demand on a water supply system is to expand the system by building new infrastructure. That is a part of a supply side improvement and management process. A completely different approach is to understand the system components, especially their characteristics and capabilities, in order to manage the relationships between them and make use of that knowledge to manipulate management strategies to achieve maximum efficiencies, thus obviating the need to resort to the commonly adopted option of new infrastructure provision. Management strategies based on the knowledge of resilience are related to the second approach mentioned above. Such strategies allow for decision makers’ timely reactions at trigger points to enable the formulation of the most appropriate management practices and also inform the correct time frame for new infrastructure development by acknowledging critical boundaries beyond which the system will not be able to function properly. The significance of this project is the exploration of the latter management approach discussed above through application of the resilience concept, in order to create new knowledge in the field of water supply. In the absence of a formal method to evaluate resilience of a water supply system, an approach was developed to link resilience characteristics of the system to a surrogate measure. South East Queensland (SEQ) Water Grid was selected as a case study to iii test the resilience of the system to climate change and population growth impacts. A system dynamics model of the SEQ Water Grid was developed and simulated under different water availability scenarios in order to evaluate the resilience characteristics of the system. The defined failure threshold was based on the demand. A set of indicators such as non-failure rainfall reduction percentage, design pressure to threshold pressure ratio (Rpp), service reduction ratio (Rss), service reduction rate (Rsp), non failure ratio (Rnf) and recovery ratio (Rrr) were proposed to evaluate the system behaviour and logistic regression analysis was used as the evaluation method for future rainfall, storage and demand conditions. For the SEQ Water Grid, the non-failure rainfall reduction percentage of 40% indicates that the system is capable of withstanding pressure (low rainfall) even for 40% reduced rainfall conditions (below average) for 50% storage. For 100% storage, the pressure withstanding capability increased up to 60% rainfall reduced conditions. In other words, the system has the ability to withstand 0.4 times above the ‘design pressure’ for 50% storage and 0.6 times above the ‘design pressure’ for 100% storage. The design pressure refers here to the level of disturbance (pressure) that the system was expected (designed) to cope without failure. The pressure in this case was the low rainfall conditions. As per the proposed indicators, the service reduction ratio (Rss) indicates the available service potential at the threshold pressure. For the SEQ Water Grid, (for 50% storage) Rss value of 0.31 indicates that at threshold pressure, the supply potential is 31%. It can also be noted that the system is capable of providing service without failure until 31% drop of output at 50% storage. For 100% storage, the system is capable of providing services without failure until 28% drop in output. This indicates that the SEQ Water Grid has the ability to operate over a considerable range of pressure without failure, which indicates high resilience characteristics. The high (above 1) service reduction rate of 1.73 and 1.2 indicates that the system behaviour as a response to pressure variation is high. For storage of 50% or above, the system’s ability to recover is very high. The system recovers within two months after a twelve month low rainfall period. This fact is justified by the high non failure ratio of 0.97 indicating that for a twelve month low rainfall period for 97% of the duration, the system is capable of supplying a iv satisfactory level of service. The recovery ratio (Rrr) of 1 indicates that after recovery, the system is capable of providing its maximum level of service. Therefore, the SEQ Water Grid is expected to perform as a high resilience system under the impacts of climate chance and increasing demand. It was also identified that loss of systemic resilience takes place at a faster rate as the rainfall, demand and storage become unfavourable. The trigger point for introducing the first level of water restrictions for the SEQ Water Grid should be when the storage levels reach approximately 40% of the capacity level. The practical value of the study is that it includes the development of methodology for assessing the resilience of a water supply system which helps to understand the dynamic nature of a system and the adaptability to a changed environment, so that the operators of the system are knowledgeable about the maximum pressure levels, below which the system operates successfully. The evaluation of assessment results obtained by the knowledge created in this study allows the prevention of catastrophic failure of the system by identifying trigger points for early actions. The practical approach to enforcing water restrictions is related to the storage levels. Therefore, by relating the trigger points to the storage levels of reservoirs, the operator will be able to formulate the most appropriate water restriction levels if necessary. v List of Publications Conference papers Amarasinghe, P., Barnes, Paul H., Egodawatta, P., McGree, J., Goonetilleke, A. (2013). An approach for identifying the limit states of resilience of a water supply system. Paper presented at the 9th Annual International Conference of the International Institute for Infrastructure Renewal and Reconstruction: Risk-informed Disaster Management: Planning for Response, Recovery & Resilience, Queensland University of Technology, Brisbane, QLD. Amarasinghe, P., Barnes, Paul., Egodawatta, P., Goonetilleke, A. (2012). Application of Resilience concept for enhanced management of water supply systems. Paper presented at the 2nd International Conference on Sustainable Built Environment, Kandy, Sri Lanka. Barnes, Paul H., Amarasinghe, P., Egodawatta, P., Goonetilleke, A. (2011). Assessing the resilience of potable water supplies in Southeast Queensland Australia. Paper presented at the International Conference on Building Resilience: Interdisciplinary approaches to disaster risk reduction and the development of sustainable communities, International Institute for Infrastructure Renewal and Reconstruction, Kandalama, Sri Lanka. vi Table of Contents Keywords ...................................................................................................................... i Abstract ........................................................................................................................ ii List of publications ...................................................................................................... v Table of Contents ....................................................................................................... vi List of Figures ............................................................................................................. xi List of Tables ........................................................................................................... xvii List of Appendices .................................................................................................... xix Abbreviations ............................................................................................................ xx Statement of Original Authorship ........................................................................... xxii Acknowledgements ................................................................................................ xxiii Dedication ............................................................................................................... xxiv CHAPTER 1: INTRODUCTION ............................................................................. 1 1.1 Background ........................................................................................................
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