Appraisal Of Plan To Irrigate Mackenzie Basin

Press, Volume CII, Issue 30196, 30 July 1963, Page 18

Appraisal Of Plan To Irrigate Mackenzie Basin

A proposed irrigation scheme could increase carrying capacity of part of the Mackenzie basin in South Canterbury from the present 16,500 sheep to slightly more than 100,000, according to a preliminary economic survey conducted by the Department of Agriculture. Such a scheme would raise the income of the area from £33,000 to £282,500.

In a letter to Mr A. D. Dick, member of Parliament for Waitaki, who is pressing for the scheme for the Mackenzie branch of Federated Farmers, the Director-Gener-al of Agriculture (Mr D. N. R. Webb) says these figures are regarded as conservative and that a 20 per cent, improvement on them should be possible. The scheme, first proposed by the Mackenzie branch of Federated Farmers, depends on the proposed hydro plan for Lakes Tekapo and Pukakl.

Irrigation canals would be drawn off a special channel which would carry water from the outlet of Lake Tekapo to the Mary Range. A special tunnel would carry the w’ater under the range, going through a hydro station before it reaches Lake Pukaki. Another powerhouse is to be at Patterson so that the race would develop power at two points, and if the proposal for an irrigation scheme succeeded it would also considerably enrich the adjacent farmlands. The total area covered by the proposed scheme is 60,600 acres, but allowing for those blocks which are capable of only 70 per cent water coverage, this is reduced to 51,200 acres, says Mr D. G. Reynolds farm advisory officer of the department of Agriculture. Fairlie. Eight Blocks The area is divided into eight blocks. Blocks 1 to 4 are situated between the main road, the- Ohau river at the southern end and an imaginary line between the Mary Range and Simons Hill. Blocks 5 to 8 are situated north-west of Simons Hill and the Tekapo river. Blocks 1 to 4 get less than 20 inches of rain a year, and Mr Reynolds says its value is reduced by the thin, gravelly, exposed soil.

Blocks 5 to 8 receive 25 to 27 in. of rain a year, and this is more effective because of better soil depth and ground cover.

“The soils covered in the possible irrigable area all have a comparatively high natural fertility. The subsoil is also of good quality and need be no hindrance where levelling is necessary. "There is no pan over any of the area. The subsoil consists entirely of silt mixed in varying proportions with gravel and boulders,” Mr Reynolds says. The area, in its native condition, is primarily sulphur deficient, but after a few years of intensive use, phosphate is necessary. Except for a marginal molybdenum response on initial legume establishment, there are no other fertiliser requirements. The area for irrigation is contained in seven runs, carrying 16,500 sheep. Allowing 40/- a head, the gross income value yearly is £33,000, says Mr Reynolds He states that 85 per cent of this income is from wool and 15 per cent, from the sale of stock. The value of cattle, small seeds, and crop from this area is negligible. With irrigation, Mr Reynolds thinks the income value from cereals would be £17,000 and small seeds would bring in £lO,OOO. He says that £20,000 could be added for the better use of adjacent areas which irrigation would permit Wild Flooding In outlining the mechanics of irrigation, Mr Reynolds says 4000 acres only of the area would be suitable for border-dyking. The remainder would have to be watered by wild flooding from contour races. The amount of fall in the land would probably be more than adequate. A tentative figure of application of four 6m waterings a year is envisaged, which allows up to 30 per cent., wastage for races and infiltration. The draw-off of water, would occur during the period of minimum power demand from October to April. "Mr Lobb” (superintendent of Winchmore irrigation research station), says Mt Reynolds, “suggests that until we know the exact fall in the land, plus the infiltration rate for the various soils, no certain figures for water requirement can be given From his remarks it would appear very doubtful whether it will pay to irrigate blocks

2 and 3 because of the high rate of infiltration. Added to this is the fact that they are approximately 40 per cent, of the proposed area and are going to supply only 15 per cent, of the added gross income,” Mr Reynolds says. The scheme should envisage full use being made of blocks 4 and 5 first, followed by block 7. At this stage 40 per cent of the potentiail area would have been developed to yield 70 per cent of the possible added production. Mr Recmolds adds: “This report takes-account of only that land capable of being reached by the intended hydro-electric canals. There are other areas in the Mackenzie to the east and south of the Tekapo river which have an irrigation potential.” In his letter dated July 5 to Mr Dick. Mr Webb says the report can be taken only

as an indication of what may occur under irrigation. A more thorough economic survey would be necessary should the farmers and runholders request an irrigation scheme. Where farmers consider a scheme is warranted, the usual procedure is for a request to be made to the Ministry of Works. The ministry makes a preliminary survey to ascertain some of the engineering problems, the Soil Bureau of the Department of Scientific and Industrial Research makes a detailed soil survey to show any problems that may arise as a result of applying water to the soils, and, Mr Webb says, his department makes an economic survey to ascertain the likely effect on physical production and net farm returns.

"If the farmers in the district are of the opinion that a scheme is desirable, it may be advisable for an approach to be made to the Commissioner of Works in Christchurch. If the Electricity Department is planning the construction of canals, the use of water for both hydroelectric purposes and for irrigation should be considered at the same time,” Mr Webb says.

Mr Dick said that this is now his intention.