Drought reinforces need for storage

January 8, 2015

We woke to mizzle – a misty drizzle – on Tuesday morning.

Holiday-makers wouldn’t have been pleased but we were delighted.

However, by mid-morning the sky had cleared and temperatures were rising.

We haven’t had a decent rain since July and it’s got all the signs of the droughts which in North Otago every few years.

Irrigation schemes using water from the Waitaki River have 99% reliability but takes from the Kakanui River are restricted and will stop altogether if the weather doesn’t break soon.

Further north in South Canterbury it’s drier still.

Less snow melt put less water in the Opuha Dam in spring and those irrigating from it are now on restrictions.

Friends near Waimate ran out of stock water weeks ago and the tanker which comes to collect their milk brings water for them.

There is nothing new about drought but the recurrence reinforces the need for more water storage:

Water restrictions for irrigating farmers look set to follow a similar pattern to the 2012-13 summer, says IrrigationNZ, when drought conditions in the North and South Island wiped more than $1billion dollars from the NZ economy.

“This summer once again highlights the need to fast track alpine-fed* water storage infrastructure in both the South and North Islands. Despite the focus upon irrigation development over the past five years, New Zealand has made very limited progress in this space,” says IrrigationNZ CEO Andrew Curtis. “We have modernised and improved our irrigation distribution systems but have failed to invest in alpine water storage to our detriment.”

(*Alpine-fed water storage refers to dams and water storage lakes that are replenished by rainfall and snowmelt within our alpine environments in contrast to streams and rivers that are fed by foothills rainfall. Alpine rainfall is more consistent and plentiful than foothills and plains rainfall, hence its suitability to provide reliable water supply).

‘We’re losing sight of the prize that reliable alpine-fed irrigation water storage could bring to both the environment and economy. Certainty of water supply allows investment in SMART irrigation technologies that greatly improve nutrient management and production. There are also direct benefits from storage including the augmentation of summer river flows or being able to release flushing flows that cleanse rivers of summer algal growth,” says Mr Curtis.

Irrigation restrictions are now widespread in Canterbury and Otago, with Hawke’s Bay dry but maintaining flows.

One of the worst hit areas is South Canterbury with the Opuha Dam, a foothill-fed river catchment, facing unprecedented water shortages. Opuha’s lake level is of major concern, says Opuha Water Supply Ltd CEO Tony McCormick. “Our situation and outlook have not improved and the lake level continues to drop steadily. Today the lake is at 31% full. We are currently on 25% irrigation restrictions and expect to move to 50% restrictions next week when the lake hits another ‘trigger’ level of 25% full. Our current predictions suggest that the lake could be fully depleted by the end of February.”

Mr McCormick says while the initial problem was a lack of stored water, the situation is now being compounded by very dry conditions being experienced across the South Canterbury region.

The Ashburton River is on full restriction which has forced the Ashburton Lyndhurst Irrigation Company to place shareholders on 85% allocation. However the Rangitata River is currently flowing at a healthy level due to good rainfall in the alps over the New Year, says Jess Dargue, ALIC scheme manager.

While some North Canterbury rivers are on restriction, Amuri Irrigation Limited CEO Andrew Barton says both the Waiau and Hurunui, both alpine rivers, are maintaining flows so scheme restrictions look unlikely in the near future.

While there are no restrictions on major irrigation schemes in the Lower Waitaki at the moment, all fed by the Waitaki River, an alpine river with storages built for hydropower, Elizabeth Soal, Policy Manager of the Waitaki Irrigators Collective says partial restrictions affecting independent irrigators are in effect on hill-fed tributary rivers including the Hakataramea, the Maerewhenua and the Awakino. There are also restrictions (some full restrictions) on some of the South Canterbury Coastal streams and waterways, including parts of the Waihao River, Buchanans Creek and the Sir Charles Creek.

In Otago, supplementary permits off the Kakanui River have ceased with the first minimum flow alert being active, and the river is approaching its absolute minimum flow, which would mean full restrictions kick-in.

Parts of North Otago are extremely dry, with the area receiving a third of the historical average rainfall since August.

“For us down here, it’s much, much drier than in 2012-13. Some are saying it’s the driest it’s been in ten years, so the restrictions will bite even harder,” says Elizabeth Soal.

While the Hawke’s Bay is dry, Hawke’s Bay Regional Council Group Manager Resource Management Iain Maxwell, says that’s not unexpected for the region at this time of the year and irrigation water availability is being maintained.

“River flows are holding well and there are no irrigation bans on the main rivers so farmers are still able to irrigate,” he says.

Drought is costly in financial and human terms. It also degrades water quality, threatens water life and can lead to soil erosion.

Drought is a fact of life for farming on the east coast but the consequences of it would be minimised with more storage to capture the excess at times of high flow for use for farming and maintaining minimum flows in water ways during droughts.


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