Don’t let water saving potential evaporate

Evaporation accounts for the biggest water losses in the nation, which means the potential shown from recent evaporation research and development, involving on-farm and major storage trials, should continue to be explored.

This is the view of Guy Roth, Program Coordinator for the National Program for Sustainable Irrigation.

The reference to evaporation R&D being recent is a matter of relativity. It is a subject which has been tinkered with for a long time but evaporation mitigation has been the focus of serious attention for less than a decade. This compares with irrigation application technologies being the subject of R&D for more than 50 years and irrigation monitoring and scheduling for more than 20 years.

Having time to test, apply and modify is a major advantage of long term research. It means good knowledge and ideas are not discarded because they don’t immediately work as well in practice as first hoped. Refinement of water application and scheduling has resulted in Australian irrigators improving production per unit of water used. Now it is clear that some of the biggest water savings can come from turning greater attention to how water is stored.
Erik Schmidt, Director of the National Centre for Engineering in Agriculture at the University of Southern Queensland has been a leading advocate for research into evaporation reduction technologies.

“The potential evaporation losses, which can be read as potential savings, from on-farm storages alone are enormous,” Erik Schmidt said.

“This is particularly so in warmer areas like northern NSW and Queensland. It is estimated that farm water storages in Queensland, for instance, equate to a total capacity of around 1,000,000 megalitres and annual evaporation can remove up to 40% of this capacity.”

He says it is important to understand where and how losses are occurring from farm dams. Situations will vary. For example, evaporation generally causes bigger losses than seepage from dams but this is not always the case.
Research has assisted determination of losses and assisted in management to reduce evaporation.

Calculations have been enhanced by measurement technologies developed in recent years. These include pressure sensitive transducer systems to measure evaporation and seepage losses from storage, which are commercialised through the Irrimate network. They work by continuously recording water depth to an accuracy of about plus or minus 1mm using units deployed in the dam. The devices can help distinguish evaporation from seepage loss. Software developed at the NCEA assists with calculations.

Other contributions by the NCEA to understanding farm dam dynamics and reducing losses include assessment of actual effectiveness and economic implications of using various products. These have included commercially available products like shade cloths, fixed covers and floating modular covers.

Erik Schmidt says that even a shade cloth can stop 70% to 80% of the potential evaporative loss (which, as earlier explained can be 40% of the total water brought into storage). Floating plastic modular covers, which can effectively cover a greater area, may reduce losses by 90% although the cost goes up from $10 to more than $30 per square metre. Assessment of value and ultimate choice will be influenced by storage size, value of crop and water scarcity issues.

“While available evaporation mitigation products have been demonstrated to be workable and cost-effective in most applications, NPSI along with the former CRC for Irrigation Futures and the current CRC for Polymers, have sought improved monolayer polymer technologies,” he said.

This has been about finding a non-structural, lower cost option. Field testing is part of the work and, as stated earlier, continuing research and practical experience in applying and managing new products will be essential for significant cutting of the nation’s evaporation losses.