How much water is in my dam?

There are a few measurements that you need to know:

  • surface area
  • maximum depth

Surface area

The surface area of a dam is calculated by multiplying the length by the width.
Example: 30 m × 50 m = 1500 m²

This will be the case for square or rectangular dams. Most dams start out as a square or rectangle, but over time appear to become rounded. If the dam is not exactly square, round the measurements off. Make sure to err on the conservative side.

Dams such as turkey nest dams can be any shape, and their dimensions may need to be approximated to calculate the surface area.

Gully dams can also be of varying shapes and the formula for calculating their storage capacity is discussed later.

Volume

With the surface area and depth calculated, the volume can then be determined:  volume (m3) = surface area (m2) × max depth (m) × 0.4

(Where 0.4 accounts for the batter slope on the sides of the dam)
Example: 1500 (m2) x 5 (m) × 0.4 = 3000 m3

To calculate the capacity of your dam in megalitres (ML), divide the volume in m3 by 1000
Example: 3000 m3 / 1000 = 3 ML

Gully dams

You can estimate the capacity of small gully storages using this formula:

Volume = (width × maximum depth × length) / 5
(Where 5 is the correction factor)
Example: Water level height up bank = 2 m
Length = 20 m, width = 10 m
Volume of excavation = 100 m3
Volume = (2 × 20 × 10 + 100)/5 = 100 m3

Width and depth are measured at the embankment site and length is the distance water will back-up (you will need to add the volume of any excavations made below water level to give the total storage capacity).

If the excavation volume is not known substitute the depth of water at the deepest point as an approximation for the depth.

Depth

Agriculture Victoria have developed a few practical tools to help you measure and calculate the amount of water in your dams. DAMDEEP measures the depth of the dam so you can do a few measurements to get an average and the online summer water calculator does the calculations for you.

Video

This video takes you through the process of making a DAMDEEP measuring tool. You can then use the measuring tool to get an accurate measurement of the depth. The video then shows how to use the summer water calculator.

Contact us or call our Customer Service Centre on 136 186

Page last updated: 11 Feb 2025