Water Journal : Water Journal November 2011
refereed paper resource management water NOVEMBER 2011 89 that most parts of the region now have one or more back-up options for bulk water supply, with full redundancy in supply to key population centres. Where a demand zone has the ability to be supplied in part from sources outside its usual supply, local water treatment plants can reduce production during water quality, maintenance and failure events. For example, where a demand zone has the ability to be supplied in full from sources outside its usual supply, any local water treatment plants can cease production during a water quality event that may impact on product water, completely avoiding a potential impact on consumers. Alternatively, the water produced from the affected water treatment plant may be able to be blended with water transferred from other sources, reducing the impacts on consumers. This flexibility also allows us to take advantage of the latent capacity in connected demand zones. South-East Queensland now has about 700,000 ML/a of treatment capacity available, compared to current demand of about 290,000 ML/a. Interconnection means that this capacity can be used in ways not possible in the past. For example, we have permanently demobilised assets of higher water quality risk. Asset utilisation is also being improved, exploiting latent capacity and thereby deferring or avoiding the need for system capital expenditure. Current Operating Strategy The flexibility outlined above means that the SEQ Water Grid can be operated in a wide range of operating modes. The preferred operating mode is specified every six months, through the SEQ Water Grid Operating Strategy. This operating mode is refined and implemented monthly, with Grid Instructions being issued to the Water Grid Service Providers. The preferred operating mode takes into account a range of issues, including: • Dam levels and water security levels; • Capacity constraints on the SEQ Water Grid components, such as maintenance; • Operating costs of the various supply options; • Water quality implications of the various supply options; • Implications of the various supply options on the resilience of the water supply system. These decisions are informed by a series of whole of Water Grid plans. This includes the SEQ Water Grid Quality Management Plan, which coordinates the management of water quality in South-East Queensland. This plan ensures that the safety and aesthetic quality of drinking water is protected; that drinking water is delivered in accordance with the Australian Drinking Water Guidelines 2004; and that these outcomes are achieved in an efficient and effective manner, taking advantage of the options the SEQ Water Grid provides. The forthcoming version includes a risk assessment for each potential operating mode, and identifies the preferred option. Current Operations Currently, the SEQ Water Grid is being operated in efficiency mode, in order to reduce operating costs and defer capital expenditure. This is made possible by supply to South-East Queensland being secure, due to dams being full or near full, new infrastructure being completed and demand continuing to be low. Key decisions to reduce the operating costs were made in December 2010. These included: • For the desalination facility, operating in standby mode. It will return to fulltime operation if the region's dam capacity drops to 60%. • For the WCRWS, supplying purified recycled water from two of the three advanced water treatment plants, with the other plant being demobilised. The scheme would be brought back online if combined dam storage levels trended towards 40%, which is the trigger point to add purified recycled water into Wivenhoe Dam. The South East Queensland Water Strategy highlights the importance of these climate-resilient supplies, explaining that the system yield would reduce from 545,000 ML/a to about 445,000 ML/a if we are not able to introduce purified recycled water into Wivenhoe Dam when key SEQ Water Grid storages fall to 40% of combined capacity. This reduction would bring forward the time at which the next source of supply is required. However, while critical to our long-term water security, these facilities do not need to be operated at capacity at all times. Rather, they can deliver this security as standby facilities -- increasing the amount that can be taken from dams when storage levels are high. This standby operation reduces operating costs and energy consumption. The key is to ensure that they remain available. For example, the Gold Coast Desalination Plant can come online again within 24 hours if needed to maintain water supply or manage quality across the entire SEQ Water Grid. It has been called on many times since this decision was made, as illustrated in Figure 1, often returning to full production within 10 hours of an instruction. At other times it produces about 25 ML twice a week, compared to a total capacity of about 125 ML/d. Emergency Response One of the major benefits of the SEQ Water Grid is that this preferred operating philosophy can be altered easily in response to any number of unplanned or external situations. For example, the ability to produce water in one subregion (e.g. the Sunshine Coast) and move to an adjacent subregion (e.g. Moreton Bay) allows increased flexibility to ensure water requirements can be met. Some examples of triggers that could potentially result in changes to the operation of the SEQ Water (cont'd overleaf) Figure 1. Desalination plant production from December 2010 to June 2011.
Water Journal December 2011
Water Journal September 2011