With ever-increasing pressures on Australia’s water resources, scientists are looking for ways to balance the needs of irrigators with those of the environment.
What they have found is that spreading water demand over the summer and winter season through new crop mixes shows the most promise as a cost-effective irrigation demand management option for improving the seasonality of flow in rivers.
“However such an option needs to include structural adjustment incentives and stable markets for winter crops,” says Professor Shahbaz Khan, Professor of Hydrology with Charles Sturt University and a principal researcher with the University’s Institute for Land, Water and Society.
Another option of making additional surface water available for the environment that showed a lot of promise was for irrigators to substitute surface water with groundwater during the peak demand months.
“However this option needs institutional reforms so that surface and ground water are treated as a single resource,” says Prof Khan who led a team of researchers from CSU and the University of Melbourne for a recent pilot project looking at opportunities to manipulate irrigation demand and supply so as to have the best possible social, environmental and economic outputs from all the available water resources within a catchment.
The project, funded by the CRC for Irrigation Futures, involved using a combination of hydrological and economic models to evaluate irrigation demand management options to improve seasonality of flows in the Murrumbidgee system in NSW to “smooth out” the current high flows in summer (to meet irrigators’ demands) and “augment” the low flows in winter when storages are filling.
The six management options identified and evaluated by the researchers with the assistance of focus group meetings early on in the project were:
- Market based reduction in surface water demand which allows for environmental managers to buy water for environment requirements at market price and provide it back to the rivers on a seasonal flow improvement basis
- Joint use of surface and groundwater through aquifer storage and recovery
- Spreading water demand with improved cropping mix that focuses on both winter and summer crops which may involve replacing rice, a major water user, with less water intensive crops in summer and spreading the water demand to the winter months
- Increasing conveyance efficiency (Canal lining) so that less water is lost through seepage, leakage and evaporation
- Increasing on-farm use efficiency by introducing various water saving irrigation practices such as drip and sprinkler irrigation system
- En-route storages which allows for dam release patterns to be changed by providing small water storage facilities closer to farmers’ fields that are capable of supplying water in peak demand.
“Linking hydrology and economic models allowed us to rank the benefits and costs of the possible irrigation management options,” says Prof Khan.
“Our findings showed that 10 to 15% of peak water demand during summer can be shaved from the annual water demand of 1400MCM. However this may result in reduced agricultural return or require private and public investments in the form of on-farm water saving technologies, canal lining or construction of en-route storages.
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