Agriculture Victoria land management extension Officer Clem Sturmfels said assessing how much water there is in a dam can be difficult due to a dam’s odd shape and formulas used to measure their volume.
“Farm dams generally hold less water than expected and in a dry year, it’s important farmers have a good understanding of how much water is left in their dams and plan accordingly,” Mr Sturmfels said.
“The volume of a dam is closely related to its length and width. A stable, well-built dam has gently sloping sides which nearly meet in the middle of the dam’s base.
“For example, a rectangular dam measuring 33m by 22m has a depth of approximately 3m and volume of approximately 1 million litres or 1 megalitre. A triangular shaped dam with similar measurements has a volume of approximately half this amount.
“Evaporation will cause a loss of around 60 per cent of this volume leaving the dam with enough water to carry approximately 200 sheep or 20 cattle for one year.
“Many dams rely on a regular top-up of water during autumn or spring, however this year has seen dry seasonal conditions, making the chance of a top-up less likely due to depleted soil moisture and less run-off.”
Agriculture Victoria has several tools to help farmers calculate dam volumes based on shape, length, width and depth, including the Farm Water Calculator and the Summer Water Calculator.
The Summer Water Calculator also helps to calculate how long the remaining water may last. Go to: https://agriculture.vic.gov.au/support-and-resources/tools-and-calculators/summer-water-calculator
The depth of a dam can be measured using a depth sounder or fishing line measuring device.
A ‘how to’ video for making and using the fishing line measuring device can be accessed on the Agriculture Victoria website.
For more information on preparing your farm for dry seasonal conditions, go to: https://agriculture.vic.gov.au/farm-management/dry-seasons-and-drought-support
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