Water Journal : Water Journal December 2012
small water & wastewater systems refereed paper technical features 64 DECEMBER 2012 water • Groundwater from the Botany Sands aquifer located within the southern part of the LGA (including seepage water evacuated from the railway tunnels); and • Seawater from Sydney Harbour. Stormwater Since white settlement, the surface water hydrology of the city has been completely altered, from natural running creeks to piped and combined wastewater and stormwater systems, to separated stormwater pipes and channels designed to efficiently convey water away from the City. In doing so the stormwater system also conveys nutrients and pollution to receiving waters and environments. In order to better understand the complex interactions of stormwater conveyance, flooding, pollution loads and stormwater harvesting opportunities, a Stormwater and WSUD Plan was developed. This plan modelled and mapped the potential stormwater harvesting resource across the city and the stormwater pollution baseline using land use planning information and MUSIC modelling software. Having established the City’s pollutant load baseline, opportunities to reduce that load were categorised according to the “four R’s” of: • Redevelopment: incorporating WSUD initiatives into major and infill redevelopments; • Retrofitting: incorporating WSUD and stormwater harvesting initiatives into existing major and minor public open spaces and private residential and non-residential properties; • Renewals: installing WSUD infrastructure with planned road, footpath and drainage infrastructure renewals; and • Reuse: where stormwater is treated and transferred to a decentralised water network for non-potable uses beyond open space irrigation. Wastewater The City of Sydney generates approximately 27GL of wastewater each year that is transferred to one of two primary treatment plants at North Bondi (to the east) and Malabar (to the south). An additional 4GL generated in external catchments also passes through the LGA. This resource (which is currently wasted and discharged to the ocean) is expected to grow by 6.4GL per year (to 33.4GL/year) by 2030. Groundwater The City of Sydney lies atop the Botany Sands aquifer. This aquifer has an area of 91km2, 14% of which is situated within the LGA at a depth of between 2m and 10m. The aquifer is potentially a source of water and a storage for alternative water harvested within the city, although further work is required to confirm the feasibility of this option. A large proportion of the aquifer situated within the Cooks River catchment is currently under a ‘domestic ban’ due to contamination issues and this is likely to be an enduring barrier to groundwater use in this area. Seawater and thermal distillation The consideration of seawater as a potential resource is related to the development of a tri-generation network plan for the city. Therefore, the proximity and abundance of seawater to the city presents an opportunity to provide cooling water and to use the waste or excess heat to distil salt water, producing an additional alternative water resource. Figure 4 illustrates the location of the tri-generation plants planned for Sydney, with their associated thermal networks. A review of the demand and supply opportunities across the City was undertaken and summarised according to Figure 5, illustrating: • Volume of non-potable demand (by City sub-catchment); and • Potential non-potable supply opportunities (by City sub-catchment). Figure 4. Proposed tri-generation network. Figure 5. Summary of non-potable demand and supply opportunities across the LGA.
Water Journal February 2013
Water Journal November 2012-1