Monday 14 December 2015


In an El NiƱo spring and summer water for irrigation is a precious commodity.  As expected irrigation started earlyish – like September - and with current predictions is likely to continue through to April.  That means irrigation will be required on a regular (aka daily) basis and will likely result in two potential issues for irrigating farmers:
a)     Groundwater users could have self-limiting bores.  This occurs when water levels drop to the point where cavitation (sucking air) occurs and/or the head required to lift water to the surface falls outside the optimum for the pump.  Both circumstances result in a reduction in L/s that can be pumped.
b)     Of greater concern is that the season is likely to be greater than the 9/10 (or 90-percentile) demand season and annual volume could be exceeded.  Therefore it is essential every effort is made to use water judiciously.

Judicious use does not include irrigating hard surfaces (aka roads).  I thought we had left the “cleaning of roads” behind – it is such an obvious waste of water and is a misdemeanour, in some cases “fineable”.  All in all not a bright use of water!

My first example is an old one and is thanks to a colleague in Hawkes Bay.  It dates back to early 2000’s, maybe 2006ish.  We have used this photo endless time to emphasise this is not the wisest use of water, and in this case a dangerous use of water.  Can you imagine riding a motorcycle and being hit by the stream of water from the high pressure gun!!  It will wash your windscreen though you could run off the road by the time you recover from the shock of the water hitting the windscreen and the wipers have been able to clear 25L/s of water.

My second example is very recent – November 2015.  No doubt the lane closest to the hedge has been well washed.  While this irrigator is less likely to result in a deluge of water on a windscreen or affect a motorcyclist as badly. It is nonetheless a waste of irrigation water.

The volume of water irrigated onto the roads is relatively small in the scheme of things.  But in a season where every drop will undoubtedly be worth $$$ in return, cleaning roads is not an effective way to make the water pay.  Quite the contrary, in both examples the water has been pumped from bores (a lost cost) and has not added any value to crop intended.

Dr Anthony Davoren,