It may come as a surprise to learn a water storage area can lose in excess of 2.5 megalitres per hectare of storage floor during the first fill after it’s been dry.

That’s why the Irrigation Association of Australia (IAA) recommends the same management of storage as for a dryland field.

The following advice was given to farmers attending the recent seepage symposium and field day at Moree organised by IAA and the Australian National Committee on Irrigation and Drainage.

To conserve moisture and reduce cracking, weed control is important. In fact, growing a crop in a storage can cause significant drying and cracking in both the embankment and the floor, with subsequent loss of valuable irrigation water.

If the storage soil surface is allowed to dry and crack, soil evaporation losses increase and significant amounts of water can be lost as it runs down the cracks and the dry soil soaks up the water.

Therefore, while storage is dry it is a good time to survey it and obtain an accurate depth-to-volume and surface area relationship.

Often the storage was not accurately built to the "design" and actual volumes can differ by up to 20 per cent.

Ideally a storage survey should be redone after any remedial construction work on the banks or any other changes to the floor or borrow areas.

Additionally, it is worth considering doing an electromagnetic induction survey at the same time to differentiate the soil types within the storage.

While your storage is dry your local surveyor can easily check it. If you have access to GPS/Beeline you can do the survey yourself and send the data to your local surveyor or engineering consultant for processing.

To do this, drive in at least two pegs at ground level located near an inlet/outlet point as reference points or bench marks. It is necessary to drive back over these points several times during the survey to establish a good level as a permanent reference height.

It is also an ideal time to install a gauge board or for greater accuracy you could set up a permanent storage meter.

Meters with pressure sensors with an accuracy of ±10mm are available, easy to install and able to continuously measure and record storage volume and water surface area.

One that is readily available and known to perform accurately is the Irrimate Storage Meter.

Knowing exactly how much water you have gives you the ability to fine tune its use and assist with water budgets.

Storage meters can also be used to get an accurate measurement of the amount of tailwater and stormwater recovered and can be used to check pump capacity when pumping directly into storage.

Once we receive some significant rain, care needs to be taken when filling a storage that has been dry for some time.

To avoid potential problems such as erosion and blow outs, dry storages should be filled slowly - no more than 300 millimetres of water a day, and preferably less than 100mm a day. 

Contact your local Cotton Catchment Communities CRC water team member.