Irrigation Matters

Assessment of Evaporation Losses and Evaporation Mitigation Technologies for On Farm Water Storages across Australia. CRC IF Irrigation Matters Series No. 05/08

Baillie, C. (2008). Assessment of Evaporation Losses and Evaporation Mitigation Technologies for On Farm Water Storages across Australia. CRC for Irrigation Futures Irrigation Matters Series No. 05/08. October 2008.

Executive Summary
Australian agriculture is highly dependant on farm dams. Storage sizes range from a few megalitres (ML) for stock and domestic supplies to larger dams used for commercial irrigation. Conservative estimates suggest that in excess of 8 000 000 ML is stored in farm dams (i.e., 9% of total stored water) and that there are more than 2 million farms dams across Australia (Australian Water Association, 2006).

Access to data on farm dams across Australia to support this estimate is relatively difficult to obtain. To account for farm dam numbers and volumes across Australia there are broadly two data sources and methods for identifying farm dams. These sources include data that is routinely collected due to licensing requirements and data obtained through remote sensing, which in the past has been specifically employed to assess the impact of farm dams on natural resources.

To determine the impact of farms dams there is a need to be able to determine the location and size of farms dams. Recent changes to legislation in various states has tightened the licensing of farm dams and therefore resulted in potentially better records. In many cases however there is still sufficient exemption from licensing, leading to under detection, which has a significant impact on natural resources. In some catchments of southern Australia overland flow diversion due to farm dams is greater than 20% (Schreider and Jakeman 1999). A significant proportion of this is through small dams i.e. ~ 5 ML that don’t necessarily require a licence. Apart from the diversion of overland flows evaporation losses from farm dams can exceed 40% of the storage volume.

Although it is generally acknowledged that the total evaporation losses from farm dams across Australia is significant, accounting for these losses is difficult given the large discrepancy between national estimates and the information collated from various state agencies and territories. To illustrate this point less than 50 % of the estimated number of farm dams can be accounted for. Similarly only 60% of the estimated volume of farm dams can be accounted for. Satellite imagery provides the best means of fully accounting for farm dams and can be used to determine the growth, location and surface area of farm dams. In particular these techniques not only provide a snap shot of farm dam development but can also utilise historical imagery to determine changes in farm dams spatially over time.

Whilst the data collated to date cannot fully account for the storages estimated nationally the data provides a useful sample in which the characteristics of storage sizes can be determined for each state. These characteristics were extrapolated to a total storage volume of 8 000 GL (i.e. national estimate) to determine the potential losses from on farm storages and the application of Evaporation Mitigation Technology (EMT). It was estimated that evaporation losses from on farm storages was 1 320 000 ML and as high as 2 880 000 ML. The employment of various EMT products could reduce these losses by 480 000 to 700 000 ML depending on the performance of chemical barriers i.e. monolayers. Given that the most significant impact on evaporation mitigation was due to monolayers i.e. potentially 350 000 ML and that performance of these products are highly variable, future research and development needs to focus on this area if potential evaporation savings are to be realised.

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CRCIF-IM-0508-web.pdf ( 1,176kb )