Irrigation critical issue — chairman

Press, 9 December 1983, Page 21

Irrigation critical issue — chairman

Irrigation was the critical part of the Acclimatisation Societies’ application for a Conservation Order on the Rakaia River, the applications hearing was told in Christchurch yesterday. Fisheries and wiidlife were important, but irrigation was critical, said the chairman of the National Water and Soil Conservation Authority committee hearing the application, Mr Clutha Mackenzie, yesterday. This was during the questioning of a witness for the Crown, Mr G. J. Harrington, an engineer in the Ministry of Agriculture, specialising in agriculture and soil engineering.

Although the applicants had been told on Tuesday to keep within time limits and that questioning of witnesses could only include “poinits of clarification” rather than cross-examina-tion, Mr Mackenzie allowed extensive questioning of witnesses whose evidence involved irrigation.

His argument was that irrigation was critical and witnesses were allowed to stray from their written evidence. On Tuesday, an Acclimatisation Societies’ witness, Mr K. F. D. Hughey, was told to stand down and produce a written summary of his evidence when he was found to be taking too long in presenting it.

Mr Mackenzie said that Mr Hughey had taken much more time in delivering it than any other witnesses after him. The societies’ restrictions on river flows would be “so severe that I could not recommend any irrigation schemes for Governn. ent approval,” said Mr W. J.

Lewthwiate, the Ministry of Works and Development engineer responsible for irrigation design in Canterbury. '

Any national water Conservation Order on the river should allow the full irrigation potential to be achieved, he said.

From the point of view of irrigation, all requirements could be met with an allocation rule in the lower river which set a minimum flow at the gorge of 50 cumecs, with any water above that to be used entirely for irrigation, he said. This is 40 cumecs below the lowest flow recommended by the societies. Their minimum flow, however, during summer months, does not drop below 105 cumecs. This would be detrimental, not only to farmers, but to the region and the nation, he said.

The North Canterbury Catchment Board’s recommended maximum of 70 cumecs to be taken out of the river at any one time was also unacceptable, Mr Lewthwaite said.

He objected to the board’s idea of a higher minimum flow during the week-ends to coincide with river users.

He suggested that recreational pursuits could be satisfied within the Selwyn River.

The use of groundwater as a major option for irrigating the plains was under much discussion at the hearing yesterday.

Mr Lewthwaite said that the Ministry of Works irrigation planning was based round the idea that onethird of the central plains would be irrigated from surface water, with the remaining two-thirds coming

from groundwater.

A Conservation Order on the river to the extent that the Acclimatisation Societies wanted would be unable to provide a reliable supply of water to any area, said Mr Harrington. This was because no supply of water would be available for between 10 to 20 per cent of the time, he said. The 50-cumec minimum would supply the irrigation schemes, if there were-, a sharing rule above the minimum giving all extra water to abstraction, he said.

Reducing the area of irrigated land would not be a likely viable alternative, he said.

The societies’ application, if it were to become law, would mean that the farmers would earn $41.5 million less than if they were allowed as much water as they wished, said a farm adviser in the Ministry of Agriculture, Mr J. P. Greer.

A 50-cumec minimum would give the region returns of $105.9 million, whereas the conservation order would give returns of $64.5 million.

One of the most important factors considered by a farmer when deciding on an investment in irrigation was the reliability of a water supply, he said. “If they have a low probability of receiving the water, they will not commit themselves and their families to irrigation development,” said Mr Greer. A town planner, Mr Malcolm Douglass, told the hearing that the North Canterbury Catchment Board’s management plan for the river ought to be completed before the setting of a Conservation Order and mini-

mum flows for the river. Mr Mackenzie asked him whether he knew that the management plan was not law, and water rights and a Conservation Order would be. Mr Douglass said he knew that, but disagreed with it.

The North Canterbury Catchment Board did not beleive that a minimum or maximum level on Lake Coleridge could be set by a Conservation Order until more research had been carried out, said its resource investigations manager, Mr M .J. Bowden.

Mr Bowden said that research he had carried out since the completion of the draft management plan had indicated that the lake had a “considerable potential” for supplementation of the Rakaia’s flows.

It could mean that irrigation interests could have the water they needed for the whole of January, and flows could be also supplemented in later months.

‘lf you do not divert water from the Harper and Wilberforce rivers, it is possible to supplement the flow by up to 35 cumecs,” said Mr Bowden. “I believe that Lake Coleridge offers considerable potential,” he said. It would be an advantage to both instream and out-of-steam users.

“A National Conservation Order would oppose any further investigations to see if the storage capacity beyond the lake’s present existing range is environmentally acceptable,” he said.

He also said that, in addition to groundwater’s being used by farmers at the moment, another 11 cumecs were available for irrigation.