Optimal long-term sequencing and scheduling play an important role in many water resources problems. The optimal sequencing of urban water supply augmentation options is one example of this. In this paper, an adaptive, multiobjective optimal sequencing approach for urban water supply augmentation under deep uncertainty is introduced. As part of the approach, optimal long-term sequence plans are updated at regular intervals and trade-offs between the robustness and flexibility of the solutions that have to be fixed at the current time and objectives over the entire planning horizon are considered when selecting the most appropriate course of action. The approach is demonstrated for the sequencing of urban water supply augmentation options for the southern Adelaide water supply system for two assumed future realities. The results demonstrate the utility of the proposed approach, as it is able to identify optimal sequences that perform better than those obtained using static approaches.

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After the embargo period  via non-commercial hosting platforms such as their institutional repository  via commercial sites with which Elsevier has an agreement In all cases accepted manuscripts should: link to the formal publication via its DOI  bear a CC-BY-NC-ND license -this is easy to do, click here to find out how  if aggregated with other manuscripts, for example in a repository or other site, be shared in alignment with our hosting policy  not be added to or enhanced in any way to appear more like, or to substitute for, the published journal article AbstractThe optimal sequencing / scheduling of activities is vital in many areas of environmental and water resources planning and management. In order to account for deep uncertainty surrounding future conditions, a new optimal scheduling approach is introduced in this paper, which consists of three stages. Firstly, a portfolio of diverse sequences that are optimal under a range of plausible future conditions is generated. Next, global sensitivity analysis is used to assess the robustness of these sequences and to determine the relative contribution of future uncertain variables to this robustness. Finally, an optimal sequence is selected for implementation. The approach is applied to the optimal sequencing of additional potential water supply sources, such as desalinated-, stormand rain-water, for the southern Adelaide water supply system, over a 40 year planning horizon at 10-year intervals. The results indicate that the proposed approach is useful in identifying optimal sequences under deep uncertainty.

In recent years, urban water systems in Australia have faced potential shortages due to recurring drought and climate change. Moreover, increasing population is leading to increasing demand in urban centres. There are many alternatives for addressing this challenge, including utilisation of different water sources (e.g. desalination, rainwater, stormwater and greywater re-use) and implementation of different policy drivers (e.g. water pricing, water restrictions and rebates for water conservation measures). However, any of these options in isolation will not be sufficient to solve the problem and the choice of the optimal combination of these strategies is a difficult task. This problem is aggravated by the need to consider tradeoffs between multiple criteria, such as security of supply, cost, energy consumption, ecological impact, public health impacts and social acceptability. In response, a general approach is proposed to sequence water supply projects, incorporating sustainability, at the regional scale. Sequencing of water supply projects involves choosing which options to implement at which stage over a planning horizon. This allows projects to be introduced when they are needed, and reduces redundancy associated with the system. In the past, the sequencing of water supply projects was relatively straightforward, as there were relatively few options (e.g. when to build the next reservoir) and the only criteria that had to be considered were water supply security and cost. However, as a result of drought, climate change and the increased adoption of sustainability principles, the problem of sequencing water supply projects has become much more complex. With the increase in urbanisation and urban infill, there is an increase in the potential to use desalination and recycled water as alternative water supply options. Therefore, in addition to new reservoirs, a large number of alternative water sources are able to be considered in the sequencing approach presented in this paper. They include desalination, stormwater re-use and rainwater tanks. Furthermore, a range of different criteria, such as energy consumption and greenhouse gas (GHG) emissions are able to be taken into account in addition to economic and water supply security criteria to decide which combination of water supply options will perform best. The approach proposed involves predicting the yield of individual water supply options and selecting which combination of sources is best in terms of economic and environmental criteria and when certain sources should be developed and brought into operation at each decision stage over the planning horizon. The proposed approach is applied to the Southern Adelaide water supply system, which has various water supply options, to demonstrate its effectiveness and its ability to provide useful information for managers of the system. The approach is aimed at providing water authorities with a clearer view of the trade-offs between competing objectives of alternative combinations of water sources and hence guiding...