Shade-cloth covers have cut evaporation from
Victorian water storage basins.

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. This is delivering a double benefit for rural communities that rely on specially constructed water basins, topped up from local rivers, for drinking water.

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 algal blooms, which are costly to clean up, and greatly reduced evaporation.

CSIRO’s Dr Niall Finn says 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.

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,” Dr Finn says.

“They would have a benefit anywhere in Australia, but there may be a limit to the size of storage you could reasonably cover; some larger reservoirs are many hectares in area and even form part of the local ecosystem.”

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 shadecloths and two were left uncovered as controls.

The trial was a collaboration between CSIRO, which conducted 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 polyethylene monofilament yarns and tapes, and supported externally by steel cables and poles from the basin banks.

Gale Pacific’s chief executive Peter McDonald says he is confident the cloths will be used by water boards around Australia, and possibly abroad. “There is also potential to use the shade-cloth covers for industrial and farming water storages,” he adds.