Considering sustainability in the planning and management of regional urban water supply systems: A case study of Adelaide's southern system

Abstract

A major challenge this century is to identify ways to reliably supply water to urban areas under the increasing pressures of population growth, urbanisation and climate change. A proper consideration of sustainability is the key to solving the urban water supply system (UWSS) problem, as it ensures that a holistic approach is taken, whereby the economic, environmental, social, technical and temporal aspects of the problem are considered. Substantial research in this field has been undertaken up to this point in time, but this has largely focused at the local and unit scales (urban clusters and individual houses, respectively), rather than the regional scale (cities and towns). There is a wide range of centralised and decentralised supply types that can be implemented at the regional scale, both conventional and non-conventional. Traditionally, conventional water supply types, such as reservoirs, dams, rivers and groundwater, have been used. However, as some of these water supplies have been over-allocated and contaminated, alternative water supplies have been developed, namely household rainwater tanks, aquifer storage and recovery, grey and black water reuse systems, stormwater reuse and desalination plants. This study presents an approach to sustainability assessment of UWSSs at the regional scale, which is applied to Adelaide's Southern water supply system. The social aspect is accounted for by exploring water allocation policies and the economic and environmental aspects of sustainability are considered by calculating the economic cost and greenhouse gas (GHG) emissions for each potential supply type, which are then combined to formulate total economic costs and GHG emissions for the UWSS. Social discounting of the economic costs and GHG emissions account for the temporal dimension of sustainability, as does a long-term planning horizon of 52 years. Finally, the technical aspect of sustainability is accounted for by a risk based performance assessment, whereby the reliability, resilience and vulnerability of the UWSS are determined. Potential supply types for the case study include reservoir supply, a desalination plant, River Murray supply and household rainwater tanks. The approach requires a water simulation model to balance the demand and supply of the potential supply type configurations and check that constraints, such as reservoir capacites and pumping limits, are upheld. Results obtained indicate that by 2060, additional water supply is required to meet the demand of the Southern system and that this would be most appropriately sourced from the River Murray because it has the lowest cost, produces the lowest GHG emissions and results in high technical performance of the system. However, because of future uncertainty over River Murray supply, water planners should also consider alternatives, such as a desalination plant and household rainwater tanks. Desalinated water was found to be cheaper but produce more GHG emissions per KL than rainwater. In terms of the risk based performance of the system, desalinated water was generally preferable to rainwater due to the high variability of Adelaide's rainfall. However, installing small 5KL rainwater tanks was found to greatly improve the technical performance of the system.