Rapid assessment of potential for development of large dams and irrigation across continental areas: application to northern Australia

Water scarcity in southern Australia and an imperative to develop regional economies have combined to renew focus on the potential for irrigated agricultural development in Australia's largely undeveloped and sparsely populated north. More than 2 billion potential dam sites across northern Australia (an area of similar to 3 million km(2)) were assessed in a consistent and objective manner, using the DamSite model, in the largest comprehensive assessment of large dams undertaken globally. Simultaneous consideration was given to large dams and their proximity to land physically suited to the development of irrigated cropping and horticulture. We did not consider regulatory and land-ownership limitations on irrigation and dam development or social, environmental and economic considerations. Although these factors do and will constrain water and agricultural development in northern Australia, each requires a site-specific analysis, and these factors can potentially change with time. Physical resources (soil, surface water, and topography suitable for large, in-stream dams) sufficient to support similar to 1.84 Mha of irrigated agriculture exist in northern Australia. This would require use of the entire yield from eight existing dams (including the Burdekin Falls and Ord River dams) and the construction of 117 new dams. A more financially attractive option could involve using water from 85 large dams (eight existing and 77 new dams) and a large number of reregulating structures (e.g. weirs) to irrigate 1.34 Mha of land suitable for irrigated agriculture. If realised, this would result in a similar to 50% increase in Australia's area under irrigation. Approximately 50% of the potential 1.34 Mha of irrigated land in northern Australia (similar to 670 000 ha) could be irrigated with similar to 20 of the more promising large dams, highlighting the declining marginal returns to dam construction and the benefits of strategic land and water resource planning. In reality, a range of regulatory, political and socio-economic factors will considerably constrain the upper physical limit to dam and irrigation development stated in this paper. They may also inevitably result in major developments occurring over longer timeframes than dam and irrigation developments of comparable scale in southern Australia during the 20th Century. Alternative sources of water (e.g. groundwater, wetlands, waterholes) and water storage (e.g. gully dams, ringtanks, managed aquifer recharge) are physically capable of supplying smaller volumes of water than large dams, although each may have important roles to play in maximising the cost-effectiveness of water supply in northern Australia.