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A robust understanding of water security, and the potential contributions made by alternative management strategies, is needed for a world challenged by population growth and climate-driven resource scarcity. This understanding is vital for realising our visions and plans to build future sustainable and resilient cities that have lesser impacts on increasingly scarce environmental and economic resources. The implications of making average demand assumptions on water security predictions and distribution patterns are investigated using calibrated bottom-up multi-scale numerical (Systems Framework) models of the Greater Melbourne and Sydney water networks and observed demand data. The calibrated Systems Framework models, which are highly spatially and temporally resolved, are progressively modified through erosion of the temporal and spatial granularity of their boundary conditions by replacing demands with various average assumptions. It is shown that average assumptions lead to material differences in model predictive behaviour, and that the directions of these differences are unpredictable and sometimes lead to counter-intuitive outcomes. It is concluded that the application of average assumptions of any kind is problematic (from both pure statistical and numerical modelling standpoints) and has the potential to heavily influence infrastructure investment and, more broadly, policy direction. [ABSTRACT FROM AUTHOR]

This investigation was motivated by revision of Australia’s national guide to rainfall run-off and flooding, Australian Rainfall and Runoff (ARR) and systems thinking about the future of urban stormwater management. Reflections on this change process revealed internationally relevant challenges and a need to reframe stormwater drainage as integrated management of the urban water cycle from a design, economic and policy perspective. Advances in stormwater management are mostly represented by demonstration projects and policies for integrated water management. Many different water management philosophies have emerged that are consistent with evolving dominant interests such as water authorities, government agencies and proprietary research consortiums. Substantial progress has been made in defining the challenges and necessary solutions but urban flooding and ecological degradation continues to be an escalating problem. Traditional drainage approaches with bottom of catchment management of quantity and quality remains a default implementation solution. Pathway dependence on past methods, competing ideas and ownership, uncertain perceptions of value and a lack of systems perspective may be a barrier that needs to be overcome by the new ARR. A systems approach is needed for water cycle management that includes stormwater management in urban areas. The insights from this paper will also apply to many other cities outside of Australia. [ABSTRACT FROM AUTHOR]

Over the last 30 years leading thinkers have taken us beyond mechanistic and reductionist analysis into systems theory and the critical boundary judgements that are fundamental to systems analysis. In defining and discussing boundary conditions, we also redefine values and facts imposed on hydrological and economic analysis that underpins decisions about government policy in water resources. The repeal of legislation for distributed interventions (water-efficient appliances and rainwater harvesting) that was previously enacted to improve the security of a regional water supply system is examined as a case study. The results of the analysis were defined by the costs and benefits that are inside or outside of the boundaries of legitimate and recognized consideration. This paper refers to those differences as boundary conditions and considers how those boundary conditions affect the outcome of analysis. Setting of boundary conditions (what is included, what is excluded and assumptions) in engineering and economic analysis dominates outcomes of decisions about government policy. These insights have general application to development of government water policy. The investigations outlined in this paper were combined to create an enhanced version of a systems analysis of a policy for setting targets for water savings on all new dwellings. It was established, using appropriate boundary conditions, that a 40% target for water savings is feasible for South East Queensland (SEQ) and provides a cost-benefit ratio of 2.1. These results indicate that a policy of mandating targets for sustainable buildings would provide substantial benefits to the state of Queensland, water utilities and citizens. [ABSTRACT FROM AUTHOR]

Source control measures include rainwater tanks, infiltration trenches, grassed swales, detention basins and constructed wetlands that can be used in housing allotments and subdivisions. A methodology for evaluating the regional economic benefits due to implementation of source control measures is presented and illustrated for two case studies in the Lower Hunter and Central Coast regions of New South Wales, Australia. It is demonstrated that use of rainwater tanks to supplement mains water supply for toilet, hot water and outdoor uses can very significantly reduce demand on mains water supply. Reductions in regional water demand will enable deferment of water supply headworks augmentation, while reductions in peak mains water demand will extend the life of water supply distribution infrastructure. In addition, substantial reduction of stormwater discharge from allotments can be realised. For the Lower Hunter region with an urban population of about 450,000 it is shown that construction of new water supply headworks infrastructure can be delayed by up to 34 years. Compared with the traditional provision of mains water and stormwater disposal, the use of rainwater tanks along with other source control measures can produce present worth savings to the Lower Hunter region conservatively estimated to be up to $67 million. Similar results were found for the Central Coast region. [Copyright &y& Elsevier]