Melbourne Park – Stormwater Harvesting System Authors Niruma Akhter, Rhys Anderson and Michael O’Neil OVERVIEW Melbourne and Olympic Park - Australia's premier sport and entertainment precinct, hosts around 600 events annually, attracting over two million visitors. The precinct is a large scale user of potable water and is on City West Water's top 200 water users list. Delivered as an integral s part of the Melbourne and Olympic Park Redevelopment Project which aims to enhance the precinct’s status as a world class sporting and entertainment precinct, the construction of the $6.9 M Stormwater Harvesting project at Melbourne Park began in 2010 and was completed by the end of 2011. The project was designed by Arup, managed by Major Projects Victoria (MPV) and constructed by Bovis Lend Lease (LL). The stormwater harvesting project was also successful in obtaining a $2.9M Federal Government Grant through the National Urban Water and Desalination Plan, under the Water for the Future initiative (DSE 2012). This paper describes the basis of design including catchment analysis, water quality and quantity monitoring, site constraints and construction challenges and achieved treated water quality. It also provides a broader picture of how the project evolved from a feasibility study and progressed through to construction. OBJECTIVES This project aims to reduce the overall potable water demand of the Melbourne Park facilities shown in Figures 1 and 2 by approximately 70% through the diversion of stormwater from the existing local stormwater drainage network, followed by treatment, storage and distribution to Rod Laver Arena, Hisense Arena and other areas for non-potable water uses such as irrigation and wash down. 1 The scheme forms an integral part of ensuring the overall sustainability of the area and the events which take place onsite. This is achieved through reduced potable water usage for irrigation and toilet flushing and reducing the environmental impact of runoff to the adjacent Yarra River. METHOD Project Feasibility In 2008, Arup conducted a feasibility study into the potential development of an integrated water recycling scheme at the Melbourne Sports Precinct (MSP) with the aim of sourcing alternative water supplies for non-potable uses in the precinct, such as for irrigation, toilet flushing and wash down. The study included the entire sporting precinct including the Melbourne Cricket Ground (MCG), Yarra River, Richmond Oval AAMI Park and Gosch’s Paddock. Figure 1 shows the various facilities at MSP before the redevelopment and Figure 2 shows the master plan for the redevelopment works. Figure 1 The various facilities at Melbourne Sports Precinct, as they were before the redevelopment works. 2 Figure 2 The early master plan vision for the precinct. The feasibility study included the determination of feasibility of the system, capital and operating costs, requirements for implementation of the system (including timeframes and indicative costs, etc.), operational and management requirements and potential partners/models for project delivery (including financing options). At this feasibility stage both rainfall dependent and non-rainfall dependent sources were considered, black water from precinct venues and nearby sewer mains being the non-rainfall dependent source. Non-potable water use data was obtained from all the sites at the sports precinct. Refer to Figure 3 which shows a demand summary. The blue curve represents demand from all the facilities north of the Yarra River and the green curve represents demand from all the facilities south of the Yarra River. 3 Figure 3 Graphical presentation of non-potable water demands. The southern part of the precinct is more heavily built up with a very high percentage of impermeable area and large networks of stormwater drains to convey and remove the surface runoff. Comparatively, the northern part of the precinct has more permeable and grassed area, Yarra Park occupying a large portion of the catchment. Thus most of the rainfall infiltrates through to the ground and cannot be captured for re-use. A nearby City West Water (CWW) trunk sewer main in Wellington Parade was found to be a reliable source of wastewater that could be treated and reused. This eventually led to the MCG sewer mining scheme, which became a separate project with a 600 kL/d underground sewage treatment plant located north of the MCG, in Yarra Park, to supply MCG, Yarra Park and Richmond Oval with Class A recycled water for irrigation, toilet flushing and wash down. The sewer mine, now known as the Yarra Park Water Recycling Facility, is currently being commissioned and is expected to be fully operational by the end of 2012 (Water Recycling Facility 2012). 4 Water Balance Based on historical rainfall data obtained from the Bureau of Meteorology (BOM), a rainfall reliability analysis was carried out for a range of rainfall scenarios for the southern part of the precinct. These scenarios formed the basis of a system reliability analysis. Additionally, a recent very low rainfall year (2006) has been inputted into the reliability model to demonstrate scheme viability should current weather patterns continue. The scenarios are shown in Figure 4. Figure 4 Generated scenarios monthly rainfall (mm). For the northern part of the precinct, sewage flow/ quantity and quality data was obtained from CWW. These data, along with the non-potable water demand data, were then used to produce a water balance. Altogether, a diverse suite of rainfall dependent and independent options and combinations of these options were considered including the option of extracting and treating water from Yarra River; extraction of groundwater from the City Link tunnels as part of the drawdown of the water table caused by the underground structures which effectively act as a sink of groundwater; stormwater harvesting and sewer mining. 5 One of these rainfall dependent options included an isolated stormwater harvesting scheme for the Melbourne Park catchments. For this particular option, Figure 5 shows the reliability of the scheme based on four different rainfall years. Based on historical rainfall data obtained from Bureau of Meteorology, one very low, one low and two typical rainfall years were selected and modelled against actual water demand throughout the year to predict the reliability of the scheme. Figure 5 illustrates that 64%-80% of the total non-potable water demands at Melbourne Park could be met by an isolated stormwater harvesting scheme within the Melbourne Park catchments, depending on the actual rainfall pattern in a given year. Figure 5 Preliminary reliability graphs for one of the Melbourne Park Stormwater Harvesting option (Very Low, Low, Typical and Typical 2). The outcomes of this feasibility study led to three separate alternative water projects, including the MCG sewer mining scheme mentioned earlier, a stormwater harvesting scheme to be located in Gosch’s Paddock fed by the Yarra Main Drain, and the Melbourne Park Stormwater Harvesting Scheme, which is the focus topic and is discussed in detail throughout the rest of this paper. The Melbourne Park site boundary is shown in Figure 6. 6 Figure 6 The Melbourne Park Site. Detailed Site Investigation and Concept Design Catchment analysis Melbourne Park, with an area of 18.3 ha is divided into four sub-catchments, as shown in Figure 7. The Western Courts already have a stormwater harvesting system in place. The Melbourne Park – Stormwater Harvesting System harvests runoff from the remaining three catchments namely: Rod Laver catchment, Forecourt catchment and the Oval (Old Scotch Oval) catchment. The blue lines in the catchment plan represent the drainage networks 7 Figure 7 Melbourne Park sub-catchment areas. Two major stormwater networks operate at Melbourne Park, excluding the Western Courts sub- catchment. One system collects all stormwater runoff (including roof water) from Rod Laver Arena (RLA), Café Arena, the Show Courts and an adjacent function building. This water is then directed to a pit located in the berm in front of RLA. This pit, (referred to as the existing pump station from this point onwards), contains two pumps that pump stormwater from the pit before discharging to the Yarra. The single point of discharge into this pump station was considered highly advantageous for tapping, requiring minimal retrofitting to capture the entire stormwater runoff from the areas it services (including the roofs). Similarly, the second network collects run off from the Oval and Forecourts sub-catchments catchments, which are also directed to a single pit before discharging out to the Yarra River. These two sub-catchments include the Oval, Hisense Arena and the Melbourne Park Function Centre. 8 Quantity Monitoring Arup engaged ADS Flow Monitoring to monitor the stormwater flows though the two trunk drains mentioned earlier to verify our initial modelling. The flow monitors were initially installed inside the drains near at the outfall end, where the drains discharge to the Yarra River. It was soon evident from the results that during high tides water from the river travels up these drains and the meters were repositioned. The actual measured flow monitoring was compared with the predicted rainfall and existing design discharge flowrate of the stormwater pump station and the model verified. Water quality sampling Stormwater samples were taken from the two largest contributing catchments to determine treatment requirements. Results of analyses are presented in Table 1. The stormwater quality from the Forecourts is understood to be of a similar quality to the Rod Laver catchment with similar activities taking place in the area. Due to the dry weather at the time of sampling and intended timelines for the completion of the concept design of the system, and the large variability in stormwater quality, operating experience from the existing Western Courts stormwater harvesting scheme and rainwater reuse system at Rod Laver was integrated in the design of the treatment system. From these existing systems, it was noted that court runoff had the potential to add colour to the water.