Farm water planning steps

Step 1: Understand total farm water requirements

Consider all possible water uses on your farm, including:

1. Household use
2. Garden
3. Stock
4. Spraying
5. Irrigation
6. Dairy
7. Processing
8. Fire fighting

Determine how much water is needed for each proposed use, in which seasons it will be needed most and the quality required.

Step 2: Evaluate the reliability of water sources and storages

Water for agricultural use can originate from a variety of sources including:

1. public pipelines
2. groundwater (usually via bores)
3. rivers
4. streams
5. farm dams
6. roof runoff

Public pipelines tend to have the highest level of reliability closely followed by groundwater. Rivers, streams and farm dams tend to dry up during periods of drought. Water collected from the roof of dwellings and sheds and stored in tanks can provide a reliable and valuable source of high-quality water.

Other risks to consider include:

1. Reduced right to access streamflow allocations during dry times
2. Reduced runoff and increased evaporation affecting dam storage as the climate becomes increasingly dry
3. Mechanical failure or loss of power affecting pumps, which is a particular risk to water reliability during bushfire
4. Failure of structures such as dam walls, or of fittings and pipes if not properly maintained

Step 3: Determine the size of storages needed

Now that water usage is understood, consider when and where that water is needed, and the size of storages (dams and tanks) required.

Section 3 demonstrates how to calculate the size of a storage required to meet particular needs, based on usage, critical storage periods (the length of time a water storage may need to last before replenishment) and evaporation rates (in the case of dams).

Also consider how much water needs to be kept in reserve and accessible in the case of a water source or storage failure. For example, this may mean having a header tank large enough to meet stock or household requirements for three days while a power outage is addressed.

How much water storage capacity do I have already?

Calculating the volume of tank storages is straightforward, but dams can be trickier due to varied shape and depth. Additionally, a dam that was built decades ago is probably not as deep as it was initially due to accumulation of silt.

Step 4: Determine how long water supplies will last during times of prolonged dry conditions

As well as understanding how much water will be used by stock, garden, household, firefighting and other uses on a farm, evaporation rates from uncovered storages are an important consideration.

If relying on dams as a primary water source, the size of dam required for it to remain in use during dry spells has increased significantly. For example, in Victoria during the last two droughts, experience, rainfall data and catchment yield indicate that dams need to be at least 4 to 5 ML in size for water to persist through two years without replenishing from runoff. A dam of this size furthermore needs to be connected to a water reticulation system to get the water to where it is needed on the farm. Upgrading a subset of dams to this size can provide greater water security, rather than relying on a greater number of smaller dams that may all be at risk of going dry. Note that regulations must be consulted before upgrading the size of any dams.

Section 3 provides average annual evaporation rates for different regions of NSW, while Agriculture Victoria’s Farm Water Calculator (see above) provides guidance on determining evaporation from farm dams. A rough rule of farm is that most dams lose around one metre per year (from the total dam surface area) in evaporation.

Remember that the final half a metre of water in a dam is probably unusable, and certainly should not be relied upon for stock water.

Step 5: Match stocking rates to water availability (water budget)

This element of farm water planning is the inverse to the step above. Given the water available on a farm and its likelihood of persistence, a realistic water budget (knowing where water is available on a farm and how much is available) is an essential component of preparing for drought.

A water budget considers evaporation from storages, seepage, native and feral animal usage, water taken for fire-fighting, and fouling. Consider not only past experience, but the likelihood of more extreme weather events under climate change.

A calculation using numbers of livestock and their predicted water intake will determine a timeframe for which the water will last. Depending on the outcome of this calculation, stock numbers may need to be reduced, or a trigger point identified for when stock numbers will be reduced during dry times in preparation for water shortages.

An additional consideration when planning for prolonged dry conditions is the impact on wildlife. Farm dams play an important role in sustaining biodiversity (including native animals, vegetation, invertebrates and aquatic life). Consider the impact on native plants and animals if all water storages on a farm are depleted during drought.

Step 6: Design farm water supply and reticulation systems

What are my options for accessing, storing and moving water on a farm?

Once water requirements are known, step back and consider the ideal setup for water supply on a farm. If current water storage on a farm is insufficient, how can this be supplemented or enhanced? What other water sources could be accessed, or other types of storage utilised? A range of engineering and technological options are now available to assist farmers in water planning.

Cost may be a barrier to redesigning existing systems, but the long-term benefit of improving water supply and storage may enable these costs to be recouped through, for example, a reduced need to destock during drought.

Investing in a farm’s water system during profitable times is a long-term investment that will pay dividends in future dry times.

Potential methods of supplementing storage include:

1. enhancing existing dams (see Section 2)
2. enlarging an existing dam or building a new dam (potentially alongside decommissioning smaller dams – check water regulations for your state)
3. increasing roof collection and storage in tanks (not all properties need a dam – rooftops provide sufficient harvestable water for small properties).

Dam water quality can be greatly improved by fencing dams and using a large fenced dam as a water source for a reticulation system. Well-designed reticulation systems are reliable and electronic monitoring systems make them considerably safer than in past decades.

Further resources for farm water planning

Download Section (Section 1)

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