Building a downsized 54,000 ML Rookwood Weir in Central Queensland, as the state government is now proposing following an estimated cost blowout, doesn’t appear sensible to me, as agricultural use of the water is critical to the project’s viability, and the project will now offer little water for agriculture (see the ABC News article Weir reduction plan condemned by central Qld farmers worried about water loss). This is not to say that the full-sized 76,000 ML dam should be built instead. Building Queensland’s Rookwood Weir Business Case suggested the full-sized project probably wouldn’t stack up anyway.
In Building Queensland’s central case ‘best estimate’ scenario, Rookwood Weir’s benefit-cost ratio was estimated at 0.6-0.8 (see Figure 1-2 on p. 16 of the Business Case). That is, the benefits from the weir were estimated to be only 60-80% of its costs. It doesn’t stack up. The project does stack up in the most optimistic “full demand” scenario, but it wouldn’t be wise to spend $352 million on a project you expect will only be worthwhile in the most optimistic scenario.
The business case for the Rookwood Weir should be re-worked, using the latest cost estimates, and the state government should give itself the option of not going ahead with the project, which doesn’t stack up in the central scenario of Building Queensland’s business case anyway. According to the Courier-Mail, the state government has already spent $66 million on the project, but the preliminary construction works start next month. These should be deferred until the government re-works the business case and is confident the project actually stacks up.