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Going bankless – a grower perspective


The reason we went with the bankless design
was we had a fair bit of new development to do on Avymore. When we surveyed it we found
that the ground was very flat; one of the bucket contractors said have you considered
bankless and we looked into it. The first section averaged about 350 metres
a hectare of dirt to move which was pretty reasonable for new country. We did 150 hectares
in 2012 – the first time it grew was 2016 due to drought. It worked really well and
that gave us the confidence to go ahead and jump into some of the other stuff and redevelop
siphons into bankless. They’re basically a top to bottom siphonless
design with a below ground bankless channel at the head ditch end 500mm below natural
field level and then a 12m batter up to the zero field grade, a 50-100m of dirt level
launching pad, then from there it just goes down the field at whatever the fall is.
Bay widths are anywhere from 180m to 420m, and you need about 30 megs a day per 100 metres
of head ditch; we’ve found about 300m is about perfect. Then at the tail drain end there’s
another bankless channel with structures in it, so we do have the capability to back tail
water up if we if we want to. One of the key considerations for us was to
minimise the cost, particularly of the structures so we’re fabricating them ourselves – it’s
been a very good drought job for us to keep a couple of guys welding in the workshop.
Our weir structures are a very simple design – they’ve got drop-down boards. We are thinking
about changing that to a door. It takes about 5 minutes to do a change (to pull all the
boards in or out), which isn’t much but when you can just have a drop-down door that seems
a lot easier. The advantages that we’ve seen – tractor operations
efficiency’s got up by at least 20-25% and also the average row length has increased
from about 600m to 1000-1200 metres in most fields so you you’re doing a lot more time
driving and a lot less turning; it’s really sped it up. The labour savings in irrigating
time are unbelievable – fill the supply channel up and give it a full gate, and it’s just
a one man operation, it’s really cut back the casual labour force.
One of the main challenges we’ve had is the volume of water required, so most of our fields
are taking 90ML a day, which is one full 26 inch pump, so if you’re watering two fields
you need two pumps, and then you’ve got a lot of tailwater, so you need a decent capacity
in your tailwater system to be able to handle that volume of water, but once you get your
head around it it’s really not that bad. The bankless head ditch is very easy to maintain,
we can just throw a grader into the bottom of these and just grade them out, reshape
them, two times a year maybe. I’d sum it up as saying that you don’t really
understand how great a system it is until first time you irrigate it, and then you realise
that all you’ve got to do is open a gate, drop some boards in a weir and walk away;
you don’t have to worry about shovelling, putting rotobucks up, throwing siphons out,
making sure they’re all running, checking your head ditch level. It’s just so simple.

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