Highbank-Barrhill farmers face an uphill climb for water

Press, 10 December 1982, Page 21

Highbank-Barrhill farmers face an uphill climb for water

An extensive irrigation scheme for 22.000 ha immediately south of the Rakaia River, which has been mooted since the 19305. still has to run a minefield of potential objections before becoming a reality. Notices of water right applications were published earlier this month and the Ministry of Works and Development is investigating the scheme. But the proposals for overcoming the geographical features of the area and bringing water to 140 farmers have laid the High-bank-Barrhill Irrigation Scheme open to assault from many quarters. When objections to the water right applications closed this week more than 60 had been received by the North and South Canterbury Catchment Boards. The scheme is bounded by the south bank of the Rakaia to the north, the Rangitata Diversion Race to the west, the old Rakaia-Methven railway to the south and the Mitcham-Rokeby Road (7km from Chertsey and parallel to the Main South Road) to the east. Although the scheme has a 20km boundary with the Rakaia. a 100 metre-plus lift from the riverbed to the Barrhill terraces in the region of the Highbank power station makes a direct feed from the river an expensive proposal. An intake higher up near the gorge has also been mooted, but there are still geographical problems to be overcome which would considerably raise the cost. So taking advantage of the planning in the 1930 s which assumed a Highbank-Barrhill scheme in the utilisation of the Rangitata Diversion Race (R.D.R.), the present proposal is to take water at least 70km from the Lake Heron region via the south branch of the Ashburton River and the R.D.R.

It is here that the minefield of objections becomes apparent. The plan calls for the Cameron River, which rises on Mt Arrowsmith and flows east to near Lake Heron before turning north into wetlands and eventually into the Lake Stream, to be diverted into Lake Heron. The lake would be used as a storage ■ although the scheme is planned to stay within the natural 1.5 m rise and fall of Heron. Then a channel would be cut from the south end of the lake, where there is a natural valley, and the extra water taken via the Stour River or by way of a channel across the Maori Lakes flats of Barrosa Station to the south branch of the Ashburton. The water would augment the Ashburton flow to the intake of the R.D.R., some 25km away near Mt Somers, where it would be conveyed to beyond Methven and the head races of the HighbankBarrhill scheme. The proposal is for. up to 15 cubic metres per second of water for irrigation to be conveyed from the Cameron to Barrhill by this roundabout route. But to take the water from the Cameron would be restricting the flow of the Lake Stream, which flows north from Lake Heron to the Rakaia River, joining on Glenfalloch Station some 60km above the Rakaia Gorge. So diversion of a maximum of 15 cumecs of water from the Cameron is depriving the Rakaia of the same amount and therefore has to be taken into account in the Rakaia River management plan. In summary, the High-bank-Barrhill proposal encompasses the following potential areas of contention: © Diversion of the Cameron is diversion from the Rakaia, so the Highbank-Barrhill scheme must join with the Lower Rakaia and Central Plains schemes in a water allocation investigation for that river. • The Lake Heron area is a noted wetlands. 9 The Maori Lakes area is a noted wetlands. • The Ashburton River is considered by many in the Ashburton County to be near maximum abstraction or over-utilised and calls have been made for some raising of the Ashburton flows by the construction of storages in the Barrosa area. • The Rangitata Diversion Race is already used by the Mayfield-Hinds, Valetta and Ashburton-Lyndhurst irrigation schemes, although it was built to include the requirements of a future Barrhill scheme. • The Highbank-Barrhill scheme uses the water features of two catchment board areas and water right applications have to be made twice. Clearly the farmers in the Highbank-Barrhill area are aware of this formidable list, F but the proposal as outlined represents their most straightforward method of getting water from the Rakaia. It is probably also their cheapest method of getting water for irrigation by any means, although the over-all cost of the community scheme has not yet been I estimated. 1 In spite of, or perhaps | even because of having some | of the deepest and best soils i on the Canterbury Plains, the Barrhill farmers have not yet taken to groundwater i wells to get water. i There is only one irriga-

tion well within the boundaries of the proposed scheme, and that has been down just three weeks. G. M. Scott, Ltd of Barrhill, drilled 150 metres at a cost of $220 a metre before finding a flow of 2250 litres a minute or 38 litres a second. Brothers Geoff and lan Scott explained that their well was 150 metres to the bottom of the screen but they proposed to pump from about 100 metres. They expect to utilise a Bisley lateral move irrigator, up to 350 m long, and with extensive re-siting of fences and ripping out of shelter belts they hope to be able to irrigate 237 ha at an all-up cost of $lOOO per hectare, including the well. The Scott farm is about 180 metres above sea level, so the well went most of the way to sea level before intersecting a deep and quicklyreplenishing aquifer. The $250,000 cost of irrigation with groundwater supplies is clearly what, has held back the other HighbankBarrhill farmers until now. Most farmers would be well aware of the potential from irrigation, however. The Scotts estimate a 20 to 30 per cent increase in wheat and barley yields and perhaps 50 per cent more peas. With good management of irrigated white clover, seed production could double or even treble. At present they plant about 50ha each of wheat,

barley and clover and around 30ha of peas each year. This over-all area planted may not change under irrigation, but the application of less than 100 mm during the critical period of November and December is expected to lift production by the estimates given. Geoff Scott expects irrigation to cost about $2O per hectare per year to run. The chairman of the High-bank-Barrhill Irrigation Committee, Mr Jack McKendry, believes the application of 50 to 75mm of water during November and December, when it can often be dry, can raise the yield potential of the area by 40 per cent over-all. It is mostly a cropping area now, with sheep being moved in during autumn and winter. 1 Mr McKendry knows through bitter experience what lack of rain at critical growing times can do. His drop in value of production from 1980-81, which was a good year, to 1981-82, a bad drought season, was $85,000. Crops that went 100 bushels to the acre in 198081, and are expected to go that much again this year, were only 30 to 40 bushels last year. Most of the area has class one loamy soils, which are free-working, have good drainage, will never present a salting problem and are arranged in ideal contours for irrigation. “The official thinking now

is that water should be put on the bettor land for the best return, rather than on the lighter, thinner soils,” he said. The proposed scheme would be totally spray irrigation, according to indications of intention from participating farmers. Recently all farmers were polled and 130 farmers out of 136 involved said they would use water if it became available. Another four were not able to be contacted and only one said he would not use the water. That one was not Geoff Scott. He said this week he would probably join the community scheme as well as irrigate from his well. “We have to get water from somewhere,” said Mr McKendry. “These soils are too good a national asset to be left the way they are. "Farmers could survive without irrigation by pulling in their horns and reducing inputs right down, but this would not be good for the country. "The social benefits from irrigation will be considerable. including increased employment opportunities,” he said. The area shows good potential for horticulture too, with the deep rich soils. Geoff and lan Scott are already planning to get shelter established quickly around four to five hectares, although they do not know what will be planted. The

area is a certified seed potato region and yields from that crop could benefit from irrigation. The Scotts will provide valuable information on the responses from irrigation in the area. They will also be five to 10 years ahead of most other farmers in the Highbank-Barrhill area. The irrigation association was revived this year after proposals for the area came to nought 50 years ago. Government departments have been working away at the scheme, calculating the, cheapest construction cost and the internal rates of return, for many years. The production of a water allocation plan or river management plan for the Rakaia and the extensive drought earlier this year prompted Mr McKendry to call the irrigation association together again.