Sequencing of water supply options at the regional scale incorporating sustainability objectives

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 them towards a more sustainable approach to water resource management.