Farm Water Calculator: Additional information

Field Measurement Guide

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What you will need

Measuring Dam Depth

Industries and Investment NSW (2008) have published an article about how to make dam depth measurer. This involves using some cord, fishing sinkers and floats, a marker pen and some plastic coloured bottle tops. The cord needs to be long enough to throw into the middle of the biggest dam on the property. One end of the cord is threaded with fishing floats and bottle tops (alternated) spaced at 1m intervals and secured with knots on either side. The floats can have the depth written on their side. Sinkers are tied to the end of the cord. Please refer to web-site: Measuring water storage volume for further information

Catchment area

Example of a catchment area using an aerial image
The catchment area is the total area of land that contributes runoff into a dam. It can be estimated with the aid of aerial photos and topographical maps. If a topographical map is used, the flow of water will follow the steepest slope which is where the contour lines are closest together. For more information about reading contour maps please refer to

Catchment area can also be estimated in the field by stepping out the length and width in metres of the catchment. Divide this answer by 10,000 to convert the answer from m2 to hectares.

Units of Measurement for Water Volumes

Information required about your property
Annual rainfall (mm/year)
Search for annual rainfall figures for your area
Annual PAN evaporation (mm/year)
Search for evaporation to see a map of your local evaporation rates

Stock type Number of animals
List each type of stock class such as milking cows, steers, nursing ewes. Maximum number of animals now or in future.
Number of Household members  
Area of each garden type in metres squared (m2)
For example the area of a 20m x 10m garden is 200m2 (multiply the length and width to give area)
Native Garden (m2
Lawn with Shrubs (m2
Vegetable Garden (m2
Other Garden (m2
Other Use of Water : Dairy Shed (please refer to publication Dairy Shed water how much do you use?' search 'dairy shed water use' for help estimating dairy shed water use) ML/year
Other Use of Water:
For example cleaning machinery, spraying, feed pad cleaning, fire fighting purposes
Other Use of Water:
For example cleaning machinery, spraying, feed pad cleaning, fire fighting purposes

Method for measuring 'Other Uses' and 'Other Sources' of water

Method 1 - Flow Rate Method - Is used to measure the flow of water from a hose or pump. It requires a stop watch and a container of known volume and knowledge of how long the water is used for.

Volume of measuring container in Litres (L) Litres
Time taken to fill container (secs) Seconds
Estimate minutes/day the water is used on this 'other use' Mins/day
Estimate the number of days/year the water is used on this 'other use'
Litres of container divided by time taken to fill L/second
L/second multiplied by 60 seconds L/minute
L/minute multiplied by average minutes spent using 'other use' water Litres/day
L/day multiplied by days/year the task is undertaken (divide by 1,000,000 to convert to mega litres) ML

Method 2 -Tank Volume Method - Can be used when water is stored in a tank or container prior to being used. The volume of water in the tank needs to be determined and then the proportion of the tank used is then applied.


For square / rectangular and gully dams measure the dam length and width in metres and for circular dams the diametre. The dam depth will also be needed for all dam types, use the dam depth measuring float / rope that you've made to undertake these measurements.

Circular Dam Rectangular / Square dam Gully dam

Dam Volume and Catchment Yield
Dam name Dam Type Depth (m) Top Dam dimensions (metres) Catchment area (hectares)
Width length Radius
  e.g. circular, rectangle, gully       For circular dams. Radius is half of the diametre or width  
Tank Volume and Roof Yield
Tank or Roof Name Tank Volume (litres) Tank Height (height) Radius (metres) Roof Area (m2)
  Please list if known, otherwise measure diameter and height of tank   Half of the diameter (width of tank) Length (m) x width (m)
Other Water Sources
Source type Description Volume
List water sources such as spring, watercourse, groundwater, town mains Provide a brief description of water source such as quality and reliability Use flow rate or tank volume method as described above to measure if this is possible. If not describe roughly how often the source is used.