Water Journal : Water Journal December 2014
water DECEMBER 2014 26 Feature article Building dams in areas with marginal water inflow risks even greater storage variability than experienced by the current water storage network. Extending into areas with less-than-ideal landscapes increases the risk of construction cost blowouts or excessive water loss through evaporation. It is probably no coincidence, then, that of the six dams to be considered for capital investment in the next 12 months, five are in Tasmania, a state rich in the essential physical (but not necessarily economic) characteristics. Do The new plans holD waTer? Most of the dams proposed for investment in the next 12 months are relatively small, with the 23,400-megalitre Circular Head in Tasmania being the largest of these. Looking ahead, there are two dams to be considered for further investment with storage estimates, including Queensland’s 880,000-megalitre Nathan Dam proposal. The largest of the 14 dams is by far Urannah Dam at 1.5 million megalitres, but it is lower down on the feasibility consideration list. These 14 dams all have considerably less capacity than existing dams in Australia, the biggest of which is Gordon Dam in Tasmania, which stores 12.5 million megalitres. There is also the question of who will pay to build them. Historically, most major Australian irrigation dam projects have been constructed by the public, and there has been little or no attempt to secure a return on the investment. For much of the 20th century, water charges for irrigation did not even cover the costs of dam operation and maintenance. It seems unlikely that many existing projects would have been economically feasible if users had been required to bear the full cost. The Ord River Scheme in Western Australia provides a good (if somewhat extreme) example. According to an official analysis, between 1958 and 1991 the government invested A$613 million in the scheme, but the benefits were just A$102 million. Yet the expansion of the project has continued (and is mentioned in the new green paper), with mounting net losses. an uncerTain fuTure Dams are inevitably linked to the climate in which they are constructed. Rainfall supplies the streams that flow into the dams, and how this relationship might respond to a changing climate is the subject of intense scientific debate. The dam’s surface area determines how sensitive the storage is to evaporation, although the actual evaporation rate depends on the local climatic conditions. If evaporation increases, this will increase the amount of water given to the atmosphere at the expense of use by agriculture or the environment. Australia, therefore, needs a dam-planning strategy that accounts for the whole water cycle, including the possible impacts of climate change. Whether or not new dams can sustain the proposed agricultural expansions in the face of these climate-related uncertainties is a critical question, especially in northern Australia where conditions are already highly variable. A useful starting point is to acknowledge that a mix of both dam and non-dam infrastructure (such as groundwater, desalination, and water recycling systems) are likely to be needed, along with water-use efficiency measures, to meet any expansion in agricultural water demand. In terms of economics, it is unlikely that future schemes will do any better than the poor return on investment garnered from Australia’s existing dams. A century of development has exhausted most of the best dam sites, and new projects will face constraints that were less acute (or disregarded) during the expansionary period of the 20th century. Moreover, while the real price of agricultural commodities has fluctuated about a stable or declining trend, the cost of large-scale construction of all kinds has increased – one of the few certainties in this entire issue. wJ This article has been reprinted from The Conversation (theconversation.com/dam-hard-water-storage-is-a-historic- headache-for-australia-33397) The auThors Joshua Larsen is a Lecturer, School of Geography, Planning and Environmental Management, at The University of Queensland. Badin Gibbes is a Lecturer, School of Civil Engineering, at The University of Queensland. John Quiggin is a Professor, School of Economics, at The University of Queensland. Tasmania’s Gordon Dam is the biggest dam in Australia.
Water Journal November 2014
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