Freeing up water for others

February 2016

Centre pivot spray irrigation at use on the farm. Photo: Aqualinc.

Catchments, where water has been fully allocated, or, worse, the capacity of the catchment has been exceeded, has recently been the focus of much media attention. New research by Aqualinc shows that irrigating with a focus on optimising a farm’s operating surplus, not maximising production, could be the key to freeing up water for new uses in fully allocated catchments.

To better understand the costs and benefits of reducing over-allocation and improving the economic efficiency of water use, Aqualinc Research investigated the effects on farm water use and operating surplus when irrigation water allocation rates are reduced relative to the rates currently used for irrigation consenting and design purposes.

“An increasing number of rivers and groundwater systems in New Zealand have limits on the total amount of water that can be taken from them, as required by the National Policy Statement for Freshwater Management 2014. In many cases, this limit has already been reached, i.e. the water body is fully allocated, or exceeded,” says Dr John Bright, Director, Research and Development, of Aqualinc Research.

“Once full allocation is reached, further economic growth that is based on water usage is dependent on raising economic efficiency – of earning more dollars per unit of water taken.”

The irrigation water allocation rate is the maximum flow rate available for irrigation, per hectare irrigated.

For soils that have the capacity to store at least 60mm of plant available water in the root zone it was found that:

  • Average annual farm earnings before interest, tax, depreciation and amortisation reduces by a relatively small amount (<2% for dairy farming) as the irrigation allocation rate reduces from 0.6 litres per second per hectare to 0.4 l/s/ha (33%).
  • Average annual irrigation water use reduces by a relatively small amount as the irrigation allocation rate reduces to 0.4 l/s/ha.
  • There was a significant drop in both earnings and water use when the irrigation allocation rate was reduced to 0.3 l/s/ha.

Dr Bright says that the key to this type of farming resilience is efficient irrigation. “These results are based on irrigation management rules that deliver high technical irrigation efficiencies on this group of soils. These types of efficiencies are achievable given modern irrigation machinery and well-proven irrigation management technologies.”

For soils whose capacity to store plant available water is less than 60mm, or for farms without highly-efficient irrigation systems, farm earnings and irrigation water use are more sensitive to changes in the irrigation allocation rate.

These findings are based on the results of computer modelling of a very large number of combinations of farm enterprise type, soil types, rainfall zones, irrigation methods and irrigation efficiencies, set in the Waimakariri water management zone in Canterbury.

For further information contact Dr John Bright,

For further information about irrigation at Aqualinc, please see: Aqualinc Research NZ, Irrigation engineering, Irrigation Consulting, Irrigation Research NZ