Water restrictions are an emotive topic. It's understandable. If you're a passionate gardener and have spent thousands of dollars on your garden, you'll be hurting right now. Hosing restrictions are hitting home. The reality is that many lawns will remain brown, vegetable gardens will struggle to produce anything and some trees and plants may not survive this summer. But bear in mind we are experiencing climatic conditions that many parts of New Zealand hasn't seen since the 1980s.
In dry spells like this irrigating farmers come under the spotlight. Many people ask why irrigation can continue when water restrictions are imposed on townies, especially irrigation that takes place during hot, windy days. Some people question whether irrigation threatens the viability of their domestic water supply and others take issue with the type of irrigators in use today, particularly the centre pivot models or "large sprinklers" commonly seen around the country.
Let's address these concerns one by one.
Firstly irrigating farmers face the same scenario as townsfolk " i.e. limited water during extended dry periods such as this summer. But resource management law gives priority to households, meaning commercial users such as farmers will always face restricted water supply first before domestic households do.
District councils make the rules for what happens with domestic water supply during dry spells. The restrictions are a combination of water scarcity and infrastructure capacity and no system is built to cope with absolute peak demand as the cost would be prohibitive. The same applies on farms. Irrigating farmers are subject to restrictions imposed by the regional councils, who base their decisions on monitoring the health and flows of local rivers and streams. An important distinction to make, however, is that the source of water for irrigation is completely unrelated to the intake and infrastructure that supports your domestic supply. So if you live in a town, city or village facing water restrictions, it's quite likely your water supply intake is under pressure and your local council's distribution system can't cope. Whereas irrigating farmers are put on restriction by regional councils to preserve the water resource they tap into. The two processes are quite separate and handled by different councils for different reasons.
When it comes to the "timing" of irrigation, farmers irrigate on a schedule so can't always stop when high evaporation conditions occur. Irrigation schedules take into account the farm's soil moisture (how dry the land is), weather forecasts (whether rain is on the horizon) and when they have access to water. If they are on a roster from a community irrigation scheme, they will need to use the water on the day it's allocated to them regardless of weather conditions, wind or rain.
Yes, there can be water losses from irrigating on a windy day but research has shown they are minimal (less than 5 per cent). The main side-effect of irrigating on a windy day is a change in the water distribution pattern. In this situation, the irrigation system, the wind's strength and the weather conditions can create challenges for plant growth. However, not irrigating would create even greater challenges for plant growth. The spray irrigation system least affected by wind is the centre pivot.
And definitely evaporative losses are being experienced this summer due to extreme temperatures. But well-designed irrigation systems and smart management by farmers and farm staff in charge of irrigation can drastically reduce water losses (in some cases to less than 10%). If we restricted farmers to only operating irrigation at night to further minimise evaporative losses caused by the sun, we'd need to double the amount of irrigators and water supply New Zealand currently uses.
We'd also need to expand the capacity of our electricity lines system to carry an increased power load so moving to night-only irrigation is simply not feasible.
Finally, some people have questioned the move to centre pivot irrigators. There appears to be a perception that centre pivots waste water. We often hear people speak fondly of the old "border dyke" systems followed by the suggestion these open race canals are more efficient at distributing water. Firstly, it's a misconception that evaporation for centre pivots is higher than for border dyke and open race systems. The reality is actually the opposite. Border dyke systems are far less efficient and lose more water than the modern spray systems. The combination of larger surface areas (open races and flooded borders) for evaporation and through ground drainage (because of the large volume of water being applied) means water losses of 40-50% are common. This is why most irrigation schemes are upgrading away from border dyke systems to improve water use efficiency and reduce water losses.
When IrrigationNZ surveyed New Zealanders two summers ago regarding their concerns about irrigation, ensuring efficient and responsible use of water was number one. Moving to highly efficient modern irrigation systems like centre pivots is a responsible move by the irrigation industry.
Water is always an emotive topic and this summer we're being reminded once again that we all need to be careful with how we use this precious resource.
It's not easy to sit back and watch your garden and lawns wither and die and see your investment in plants, trees and vegetable crops go to waste. So imagine this on a larger scale. Farmers and growers' very livelihoods throughout the nation, especially in eastern areas, are now at risk due to these very dry conditions. The drought two summers back cost New Zealand more than $1 billion.
Protecting the health of our waterways and the overall water resource is the reason gardeners, urban households and irrigating farmers alike face water restrictions.
Let's hope the crops that feed our children and grandchildren from numerous well-tended gardens, and through arable and stock farming that provide the basis of our economy, are able to ride out this climatic event and bounce back. We all need to support each other this summer and hope for rain for all our gardening and farming enterprises.
-Andrew Curtis is CEO of Irrigation New Zealand
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