# Do your dams still hold the same amount of water?

**Greg Bekker, Agriculture Victoria, Benalla**

With last year’s wet winter, wet spring and then floods your dams may not have collected just water.

With the large volumes of water flowing across your paddocks, from local rainfall, flooded rivers and creeks a huge amount of soil and sediment has been shifted across the landscape. If this is now in your dam, you have lost water storage capacity.

When you look at your dams all you see is the water. The dam may be full or have dropped half a meter around the bank. How much water do you still have left?

What has happened under the water? Doing some measurements may help you make decisions about your dams and water situations. Allocating funds and getting contractors to do work is costly and takes time. Not having the amount of water, you thought you had during the next dry spell may be more so.

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.

How deep are your dams? Has sediment built up in the bottom of your dams, or is it still is deep as you thought?

How do you calculate how much water you have stored in your dams? It is reasonably easy to measure the length and width of your farm dam.

Measuring the depth of your dam is much more difficult.

Dam deep is a simple measuring tool I'm going to show you how to make yourself so that you can accurately measure the depth of your dam... safely.

What you will need is some 10 to 20 lb mono line. You'll need some lumo beads. You'll need a sinker with a swivel on it. That's really important cause it stops the line from twisting.

You'll need a float, and you'll need a pair of scissors to cut the line.

So to build this you need to put this in order. Where you have the small bead, the larger bead, the float, the larger bead again and the sinker... and then it's a matter of threading those through and doing it.

So the small bead on first, then the large bead, then through the float.

Through the next bead and then tie a good knot onto the sinker so that it doesn't come undone. This top bead which is slightly smaller you need to have that so that it will slide up and down the main line, but will

also stay there so to do this you grab a piece of extra line, and thread it through that.

And you might need to do this a couple of times until you get the required resistance. Now I've put that through twice and you can see now, but the bead is sitting there.

It will still slide. So the way to check that is ... the float sitting on the water ... and there's the bead sitting up there.

The important thing here is, when you throw this into the dam that sits on the top of the water, the sinker hits the bottom. That's the depth of your dam.

So now we're ready to go out and start measuring some dams

So once you're at your dam site, and you've measured the length, and you've measured the width, you can then use your Dam deep tool to actually measure

the depth.

So you just simply stand here in an underhand motion, and throw it out to the centre of the dam.

The float will hit the surface and the sinker will go down to the bottom. Then it's just a simple matter of retrieving it. Top bead has done it's job and stayed at the top of the float.

It's job and stayed at the top of the float so from there to the bottom of the sinker is your depth, approximately one, 1.1 metres. And get a tape measure to measure that.

The edges of the dam can be slippery and wet, so please take care at all times. This is best done with two people. 1.4 right, good, thank you.

So now you know what your measurements and for this dam. We've done 4-5 measurements. The depth is 1.4 metres.

we've taken the length, that is 20 metres and the width is 18. We can now put those figures into the online calculator and come up with an accurate measurement of how much water is in this dam.

We go to the Summer Water Calculator. Press start and then it asks you for the storage name, which is Shearing Shed. Type that in, we pick the water storage shape

and in this case it's a round or elliptical dam. Then you scroll down and it asks you for the width, which we said was 18 metres.

The length is 20 metres and the depth is 1.4 metres. The calculation is done for you and in this case it's 158000 litres or 0.16 of a megalitre. You now have the tools to calculate the volume of water in

all of your farm, dams.

This will help you make better water decisions for now and into the future.

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 to determine how much water you have in your dam.

For more information, contact Greg Bekker at greg.bekker@agriculture.vic.gov.au or on 0417 340 236.