The substantial growth in world demand for Queensland coking coal has seen a number of new coal mine developments in the Bowen Basin in recent times. The Bowen-Broken Water Supply Scheme (BBWSS) is presently based on water supplied from Eungella Dam and storages at Collinsville to two major pipelines. In early 2004, three successive years of well-below average rainfall had left Eungella Dam at critical levels, threatening the region's mines, which rely on it for their essential water supply. SunWater noted that without significant inflows into Eungella Dam, or the development of a new water supply to the region, existing mines would be severely restricted in water supply, and downstream economic impacts to the region would follow._x000D_
SunWater investigated the opportunities for additional supply capabilities, including combinations of off-stream storages, additional pipelines, and raising Eungella Dam. An off-stream storage (OSS) was selected as being the preferred option to improve the reliability of the system and head off impending falls in announced allocation for the system._x000D_
The integrated quantity quality model (IQQM) is the Queensland Government's preferred model to define and assess total catchment performance against water security and environmental objectives. Modelling of the performance of the water supply system, with and without the proposed OSS, was required to provide justification to the customers of the system that the OSS was in fact required, and also to optimise the configuration of the OSS within time and budgetary constraints. In the case of the BBWSS, no environmental base flows are dictated by the Department of Natural Resources, Mines and Water (NRM&W) at present and the primary reason for applying IQQM was therefore to investigate the trade-offs between supply options and reliability._x000D_
SunWater produced IQQM outputs for a range of scenarios for the proposed off-stream storage, and these IQQM outputs were then used as input to a decision-support tool based on the GoldSim modelling package. The GoldSim model was then applied to investigate the water supply reliability for high priority users resulting from various existing and/or proposed water supply infrastructure configurations coupled to the hydrologic system._x000D_
The GoldSim model included the ability to assess the long-term water supply reliability impacts for each of the water supply end-users for a wide range of user-defined scenarios. Non-technical model users were able to change the size of the off-stream storage, pipeline capacities and assumed climatic conditions and test for themselves the relative benefits (in terms of water supply reliability) of different infrastructure configurations under consideration._x000D_
The decision tool was of significant benefit in assisting the decision process to SunWater's mining customers. These customers needed to decide if they felt that the increased reliability in their water supplies from the system that would be created warranted the estimated increased charges that would require to be levied to recover costs of the new infrastructure with appropriate profit margins._x000D_
The conjunctive use of IQQM and GoldSim was successful in demonstrating the impact of both hydrological and non-hydrological issues on the future water supply reliability in the BBWSS and resulted in a decision to proceed with the construction of a new OSS._x000D_
FORMAL CITATION:Davidge, S, Jha, A and Merz. R, 2006. Conjunctive use of water supply modelling in the evaluation of future performance of a planned off-stream storage for the North Bowen Coal Basin, in Proceedings Water in Mining 2006, pp 225-232 (The Australasian Institute of Mining and Metallurgy: Melbourne).