Night-time Evaporation Proves Significant Issue for Farm Dams

New research has found that the rate of night-time evaporation from farm dams far exceeds previous estimates - in fact almost half of evaporation losses - forcing a significant re-think on design and construction to ensure efficient storages.

The study was funded by the National Program for Sustainable Irrigation (NPSI) and conducted by Matthew Hipsey from the Centre for Water Research at the University of Western Australia. The results have been launched this week in Darwin at the conference of the Australian National Committee on Irrigation and Drainage (ANCID). After modelling ten dams in four different climatic regions, it’s been found that, irrespective of a dam’s size or the climatic region in which it is located, between 35-45% of the total annual loss of water through evaporation occurs during the night.

There was significant seasonal variability, with predictions for a considerable increase in the night time contribution during the winter months at all sites to between 55 and 70%. South west WA displayed the lowest night time contribution (36%) and Murray-Darling Basin region of Queensland showed the highest (44%). Both northern Victoria and the Barossa region of SA showed contributions of approximately 40% over the simulated year.

However, the analysis concluded that climate and dam shape have little to do with the fraction of evaporation occurring during the night time so it is an issue irrespective of where you are. "Evaporation losses from farm dams are a major potential area of real water savings," Mr Hipsey said, "as roughly one-third of water captured nationally is lost through evaporation." "What this study shows is that evaporation is a constant, not just a day time issue, and many methods used in the past to calculate losses to seepage will have to be revised. "To reduce evaporation, ensure the dam is sheltered from sun and wind, and minimise the surface area to volume ratio."

The study used the Centre for Water Research’s "Dynamic Reservoir Simulation Model" (DYRESM). As part of this project, DYRESM was upgraded for irrigation storages and is now available freely online to help engineers and farmers design more efficient dams. More details of the research are available through the National Program for Sustainable Irrigation website: www.npsi.gov.au. NPSI is focussed on research that will drive the development and adoption of sustainable irrigation practices in Australian agriculture. It is managed by Land & Water Australia on behalf of its fourteen partners.

For more information, please contact:

Murray Chapman, National Program for Sustainable Irrigation on (03) 5763 3214; email: rplan@benalla.net.au