Water Week

EWN Publishing

CSIRO cuts evaporation with water basins cover of special semi-permeable shade cloth; evaporation drops 10-fold in Vic test, from 29 megalitres to 2.9 megalitres

Posted by waterweek on 14 September 2007

A project to shade water basins to stop toxic algal blooms from forming has had an unexpected, but welcome, outcome: water loss from evaporation has also dropped dramatically, according to CSIRO publication SOLVE.

No algae: A solution to the problem – exposure to the sunlight that promotes algal blooms – has been to cover water basins with a special semi-permeable shade cloth. In a two-year $1 million trial the covers successfully inhibited the algal blooms, which are costly to clean up, and greatly reduced evaporation. CSIRO’s Dr Niall Finn said that shade cloth, which can be suspended above the water so maintenance work is not hindered, blocks 98 per cent of the light. This prevents the algae from photosynthesising.

And less evaporation: This was the expected outcome, but the bonus has been the effect on water storage. In the Mallacoota basin in Victoria, evaporation loss fell from about 10 megalitres a year to just one megalitre. Across all the covered basins evaporation was cut 10-fold, from 29 megalitres to 2.9 megalitres. “These shade cloths can be used anywhere and would be especially valuable in hotter areas where evaporation is even higher and algal bloom incidences are more prevalent,” Finn said. “They would have a benefit anywhere in Australia, but there may be a limit to the size of storage you can reasonably cover; some larger reservoirs are many hectares in area and even form part of the local ecosystem.”

Experiment to test shade cloths: From 2004, six water basins within East Gippsland Water’s region were monitored for two years. Four of the basins – at Omeo, Swifts Creek, Mallacoota and Cann River – were covered with shade cloths and two were left uncovered as controls. The trial was a collaboration between CSIRO, which conductetd the research, Gale Pacific, which made the shade cloths, Superspan, which made the cover structures that held the cloths in place, and East Gippsland Water. The shade cloths had to be strong, durable, UV-stable, resistant to abrasion, flexing and heat, and be able to sustain tension for long periods in extremes of heat and cold and in windy conditions. They are knitted from high-density polythylene monofilament yarns and tapes and supported externally by steel cables and poles from the basin banks.

Ready for use everywhere: Gale Pacific’s chief executive Peter McDonald says he is confident the cloths will be used by water boards around Australia, and possibly abroad.

Reference: SOLVE August 2007. Telephone enquiries: 1300 363 400; email: solve@csiro.au; website: http://www.csiro.au

Erisk Net, 13/8/2007

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