Cuan Petheram

Persistence of in-stream waterholes in ephemeral rivers of tropical northern Australia and potential impacts of climate change

Many northern Australian rivers have limited or non-existent dry season flow and rivers tend to dry to a series of pools, or waterholes, which become particularly important refugial habitat for aquatic biota during the periods between streamflow events. The present study developed techniques to identify in-stream waterholes across large and inaccessible areas of the Flinders and Gilbert catchments using Landsat imagery. Application of this technique to 400 scenes between 2003 and 2010 facilitated the identification of key waterhole refugia that are likely to persist during all years. Relationships for predicting total waterhole area from streamflow characteristics were produced for four river reaches. Using these relationships and streamflow predictions based upon climate data scaled using 15 global climate models, the potential impacts of future climate on waterhole persistence was assessed. Reductions in waterhole area of more than 60% were modelled in some years under drier scenarios and this represents a large reduction in available habitat for areas that already have limited in-stream refugia. Conversely, under wetter future climates the total area of waterholes increased. The approach developed here has applicability in other catchments, both in Australia and globally, and for assessing the impacts of changed flow resulting from water resource development.

An automated and rapid method for identifying dam wall locations and estimating reservoir yield over large areas

Global demand for water, food and energy has seen the construction and planning of large dams continue at a steady pace in many parts of the world. However, the process of exhaustively examining all potential dams sites within an area as part of an initial scoping study is still largely undertaken using manual methods. This paper describes DamSite, a series of novel algorithms that construct virtual dam walls at every pixel along every channel within a catchment, including saddle dams where required by the terrain. By repetitively calculating dam and reservoir dimensions, reservoir yield and dam costs along a river network and for incrementally higher dam walls at each location it is possible to identify both optimal dam wall locations and optimal dam wall height at a given location. The DamSite model was tested in two catchments in northern Australia and accurately pin-pointed previously identified potential dam locations. Model automatically identifies and evaluates all potential dam sites in a catchment.Calculates reservoir surface area, capacity and yield and dam dimensions and cost.At each site it calculates the height at which the yield to cost ratio is highest.Model output can be conveniently used to rank sites for more detailed investigation.The model accurately pin-pointed the more promising dam sites in testing.

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 ~3 million km2) 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 ~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 ~50% increase in Australia’s area under irrigation. Approximately 50% of the potential 1.34 Mha of irrigated land in northern Australia (~670 000 ha) could be irrigated with ~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.

A Method for comprehensively Assessing Economic Trade-Offs of New Irrigation Developments

To meet the anticipated increase in global demand for food and fibre products, large areas of land around the world are being cleared and infrastructure constructed to enable irrigation, referred to herein as ‘greenfield irrigation’. One of the challenges in assessing the profitability of a greenfield irrigation development is understanding the impact of variability in climate and water availability and the trade-offs with scheme size, cost and the sensitivity of crop yield to water stress. For example, is it more profitable to irrigate a small area of land most years or a large area once every few years? And, is it more profitable to partially or fully water the crop? This paper presents a new method for efficiently linking a river system model and an agricultural production model to explore the financial trade-offs of different management choices, thereby enabling the optimal scheme area and most appropriate level of farmer risk to be identified. The method is demonstrated for a hypothetical but plausible greenfield irrigation development based around a large dam in the Flinders catchment, northern Australia. It was found that a dam and irrigation development paid for and operated by the same entity is not, under the conditions examined in this analysis, economically sustainable. The method could also be used to explore the impact of different management strategies on the agricultural production and profitability of existing irrigation schemes within a whole of river system context.