What to do about an evaporating dam

Throughout the warmer months, it's essential property owners monitor water storage regularly to help them understand how much water their stock are drinking and what may be lost through evaporation or leakage.

Farmers should identify which is having the greatest impact – water used through stock consumption or water lost through evaporation or leakage.
Have you simply run out of water because there has not been sufficient rainfall to produce the required run-off?

To generate run-off into storages, rainfall events typically need to exceed 20mm. If grass height is over 50 mm, you may need 60 mm or more per event. Many regions have not had these types of events for some time.

Identifying and managing leakage
Leakage from dams often shows up as wet spots or clumps of green grass in a small area during the drier part of the year. This can occur when dry dams fill quickly but dam walls haven't fully re-saturated.
If farmers suspect leakage, consider using treatment products but choose carefully, as many are soil-type specific. Landowners will get the best value when you take this into account.

If farmers treat their dam, ensure the dam is properly fenced to exclude all stock. Storage treatment products can range from $1000 to $10,000 and should only be used when farmers are certain that your storage is leaking.
Also, consider safety: add steps or structures to the inside batters to help animals or people exit safely without damaging the treated batter or liner.

Understanding evaporation
Wind has the biggest effect on evaporation. Even in good seasons, property owners can lose up to 0.75m of water, often half the dam's volume.
Shallow water (less than one metre deep) warms quickly, increasing evaporation. Dams deeper than three metres retain cooler water and lose less to evaporation.
There are a variety of materials that could be used to cover the dam surface area to minimise evaporation further. Powders, oils and polymers are all affected by wind blowing the product to one side, reducing effectiveness. Plastic sheets, discs and balls are options but also expensive and can cause small animal entrapment.

Expanding or consolidating storage
Storage enlargement is not always an option due to factors such as soil types, contractor availability and seasonal timing for earthworks, a project which can run into the tens of thousands.
Measuring, calculating and adjusting water use according to what is available and stock needs is generally the cheapest option.

To work out how much water you currently have available, the measuring the depth of your dam video on the Agriculture Victoria YouTube channel provides simple instructions.
This will give you a 'right now' picture of your situation and allow you to plan for the near future.
The Farm Water calculator mentioned in the video will help you with your storage capacities potential when full.

Other considerations:
Are your dams suitable for the current stock type?
Do you have a bore or tanks that could replace your required water supply for stock?
Could I combine low storages into one larger storage to minimise evaporation and maintain water quality? Moving water using poly pipe and a fire pump is a low-cost way to do this and it can work well with trough and pipeline systems too.