The primary objective of this project was to explore, quantify and cost the opportunities for alternative water sources across Melbourne in a strategic and systematic way, taking into account the spatial variability inherent in these opportunities. Spatial factors impacting on alternative source opportunities include:
- Resource availability
- Storage opportunities
- Delivery infrastructure
- Demand for water
- Potential to reduce harmful discharges to waterways
- Potential avoided costs
The study was also designed to score and rank the alternative water supply options in regard to factors that take into account the wider social and environmental impacts of the source. A secondary objective of the study was to engage with the Metropolitan Melbourne water businesses in a meaningful way to make best use of the collective knowledge of the industry and to make the outcomes relevant to them.
The Alternative Water Atlas was developed in four key stages:
1. Demand: In order to assess the opportunities for alternative water sources, the location and volume of non-drinking water demands was mapped across the city. Demand was mapped for four time slices: 2012, 2018, 2030 and 2060. Non-drinking waterdemand includes:
- Residential non-drinking water demands (existing, new development and Principle Activity Centres and Central Activity Districts)
- Commercial and industrial
- Public open space and sports fields (golf courses)
The existing city footprint was used as the foundation for the demand mapping. To build on this to 2018, and then 2030, the Urban Development Plan (UDP) data was used to identify areas of future residential and industrial growth. This was extended to 2060 in consultation with Growth Areas Authority, the Department of Primary Industries (DPI) and the Department of Planning and Community Development (DPCD).
2. Supply: Four alternative water sources were analysed as part of the development of the Atlas:
- Rainwater harvesting
- Stormwater harvesting
- Recycling from a treatment plant
- Sewer mining and black water treatment plants
3. Environmental values: One of the key drivers for the wider adoption of alternative sources is the potential that schemes could provide environmental benefits. In order to analyse the potential environmental benefits of alternative source projects, environmental values were mapped across the city. These layers identified where the use of alternative water could have a positive or negative impact on the environment. This includes consideration of where the water is harvested from, as well as issues associated with the discharge of water back to the environment.
Three key environmental values were mapped: environmental flows, urban stormwater and receiving water quality. This work was based on the Trajectories Reports developed as part of the Healthy Waterways Strategy (The Trajectories Reports (Alluvium) are a key input into the Healthy Waterways Strategy and cover key topic areas including birds, fish and platypus. These species are considered indicators of environmental conditions).
4. Opportunity assessment: Over a thousand potential decentralised supply options were considered in the development of the draft WSDS. The sheer number of options meant that it was not feasible to individually analyse the potential impacts of each option. For this reason a rapid assessment methodology (RAM) was developed. The RAM was designed as a systematic, transparent and repeatable method that would represent the environmental and social impacts of each alternative water source across the project area.
Criteria were developed through a workshop attended by 30 water industry representatives. The selected criteria were: yield, reliability, net unit cost, land ecosystems, solid waste, environmental flows, urban stormwater impacts, water quality, energy, flood mitigation, perception of human health risk and resilience. Each criterion was weighted by workshop participants using a pair wise comparison.
The outcome of this work was two fold. In the first instance the analysis provided an insight into the potential opportunity for alternative water sources across Melbourne now and in the future, and the costs and benefits that attach to these opportunities. The second output is a spatial planning tool (the Atlas) that can be used into the future. The Atlas examines potential opportunities for local scale use of alternative water based on:
- resource availability;
- storage opportunities and delivery infrastructure;
- potential to reduce harmful discharges to waterways; and
- potential avoided costs (e.g. cost/energy of supply from the centralised system, cost/energy of waste-water removal through the centralised system).
Potential opportunities can be analysed using the Rapid Assessment methodology. The assessment methodology analyses the potential social, environmental and economic impacts of potential options to recommend the preferred supply option at specific locations. This does not replace the need for detailed analysis, but provides a valuable snapshot of where opportunities exist across the city. There is an opportunity for this Atlas to be made more widely available into the future to enable third parties to analyse future opportunities.