Saving water with dam covers
On the Granite Belt, the last drought really drove home the value of protecting our stored water from evaporation. Some of the most effective ways to protect this water can be seen with local growers employing evaporation mitigation technologies, as these have already helped with the continuity of their business in times of drought.
At the Stanthorpe Node, we worked with local growers and Michael Scobie (Senior Research Engineer) and Erik Schmidt (Honorary Industry Fellow) from the University of Southern Queensland, both of whom have carried out activities in the local area to conduct research, develop a factsheet and Granite Belt-specific case studies to help growers improve their drought preparedness. You can read these case studies on our website.
There are a range of options available for Granite Belt growers to reduce their evaporation loss. Using suspended or floating covers and chemical films may reduce stored water losses if the right product is selected for a specific water storage. In the Granite Belt Region of Queensland – where horticulture production is dominant – evaporation from storage is typically between 1.6m and 1.8m/year.
The value and cost of water in Australia has increased significantly and evaporation is usually the largest component of loss from rural and urban water storages. The depth of most Queensland farm storages is less than seven (7) metres, and most have a surface area of less than 2ha, with evaporative loss accounting for 30-40% of the total volume held in the storage. Reducing this loss, especially during a drought could be the difference between a profit and a loss for the season.
It is important to understand exactly how much water you are losing. To start, you can measure your evaporation and seepage losses. Evaporation rates can be estimated from regional climate information and/or accurately measuring changes in stored water levels between periods of pumping, or rainfall. Pressure sensitive transducers (PSTs) can be used to precisely measure water depth and accurately determine the seepage and evaporation components when used in conjunction with a local automatic weather station. There is also an effective online tool where you can estimate your evaporation using local historical evaporation data. Not only will this tool give you an understanding of your water loss, it can calculate the cost to mitigate this loss, which can be added to your Farm Business Resilience Plan.
Once you have this information, and therefore know the scale of the issue for your operation, there are a number of structural and storage management options. This ranges from raising storage wall heights, and a range of commercial product options including suspended, floating, or modular covers, or chemical films.
As noted by UniSQ Senior Research Engineer Michael Scobie, “the annual cost of an evaporation mitigation technology needs to be considered in terms of cost per megalitre saved. This is calculated using the capital cost of the product installation and annual maintenance costs, offset against the annual and seasonal water saved from the storage, as well as storage operating conditions and requirements, and the efficiency of the technology in reducing water loss.” For example, in the Granite Belt area of Queensland, the annualised cost of a suspended shade cloth cover, saving 85% of evaporation, with a fabric life of 15 years and capital cost of $13/m2 would be around $700-$1,000 per megalitre of water saved. This increases to around $1,700-$2,000 per megalitre for a cover costing $30/m2. Given the high value of horticulture products on the Granite Belt, and the high cost of purchasing replacement water, this could be considered a viable option for horticultural farmers who would also benefit from water quality improvements from a covered storage.
In our two case studies, you can read more about the options utilised or considered by two local farming families. The Taylor family have developed an interconnected series of water storages on their farm at Amiens, and the Andreatta family at Stanthorpe have a suspended shade cloth dam cover that has been in operation for 19 years. During the most recent drought, when some irrigators (and the town of Stanthorpe) had to truck in water, the Andreatta family were able to irrigate from their covered storage, safeguarding production levels.
Farmers locally consider this one of the most effective methods of safeguarding their future through times of drought. Consider using these UniSQ tools for your future planning and decision making. Our Hub and partners will continue to scan for opportunities that address evaporation mitigation technologies locally and further afield.
Where you can find out more
Factsheets and case studies - You can read the fact sheet and full case studies developed for the Hub on our website.
Handy web tool - An easy-to-use web tool https://evapadvisor.com/ has been developed for undertaking site-specific analysis to inform potential users of the cost-benefit of each technology.
Evaporation mitigation assessment - A detailed report providing an assessment of evaporation mitigation technologies in Queensland was prepared by UniSQ in 2020 through funding from the Queensland Government, read it here.
More information
If you have further questions, contact the SQNNSW Innovation Hub’s Stanthorpe Node Manager, Wim Linström, on 07 4685 5005 or email wim.linstrom@unisq.edu.au, Or UniSQ’s Michael Scobie email michael.scobie@unisq.edu.au.
The UniSQ-led SQNNSW Innovation Hub receives funding from the Australian Government’s Future Drought Fund.