Irrigation Project On Old Riverbed

Press, Issue 32345, 10 July 1970, Page 8

Irrigation Project On Old Riverbed

Irrigation is changing the face of a very light and stony block of country at Ashburton Forks, about 19 miles from Ashburton. After only one year of watering the carrying capacity on part of this property has been lifted from one to four sheep to the acre and an ultimate carrying capacity of at least six and even up to 10 sheep to the acre may not be too much to expect on the more favoured areas,

However, the pathway to this sort of improvement has not been clearly defined and a good deal of trial and error has been necessary in developing this country for irrigation. The block of 1040 acres, described as 75 per cent to 80 per cent old riverbed, was taken up in 1961 by Mr F. W. Newton, who moved to Mid-Canterbury from the Fairlie district after also farming at Winton in Southland. It was then carrying only 800 sheep and Mr Newton, who works the property with the help of two sons, Messrs J. F. and R. C. Newton, believes that the maximum capacity of the property under dryland farming was reached when the flock rose to 1350. Under these conditions the grass grub and the porina caterpillar thrived, setting a definite limit on further development and even lucerne did not do well in these harsh conditions. But when he took over the property Mr Newton was conscious of the two miles and a half of frontage to the North Ashburton River and the possibilities for irrigation that this offered. However, before any water could be taken for irrigation the South Canterbury Catchment Board had to be satisfied that as a result of river protection works along the frontage there would be no threat to landholders down country of the river breaking through and endangering them in the event of a flood. At the time the property , did not come within the boundary of a rating district ; for river development and protection. The Newtons began river protection within days of coming to the property and have spent at least $6OOO on bank protection. Groynes 1 have been built, tram and railway rails have been driven into the banks, wire | : ropes joined to them and I willows dragged up to two ; ■ miles and a half to anchor ) to them, and thousands of poplar poles have been planted. Incidentally, two tractors have had to be written off after they were caught in the river. Through the Catchment Board the State has also contributed some 84000 to $5OOO to the work in the form of subsidies. When most of the work had been completed and authority already given for diverting water from the river the farm was classified and brought into a rating area. Because of its undulating and broken nature, characteristic of old riverbed, and the thin soil covering ranging from a mere inch to about four inches, this country has not been easy to develop for irrigation. Discussions about it began with Winchmore irrigation research station staff as river protection works neared a stage when irrigation could be contemplated. The initial inquiry was about the sort of results that might be expected from irrigation on this country and it was envisaged that within two years it could be converted from one to four sheep to the acre country. In fact this result was

achieved in one year where | water was used. On this basis and with I the knowledge that there! was no other alternative if I the property was to carry I any more stock, the decision I was taken to proceed —I Winchmore promising all | the help it could give. Because of the difficult nature of the country the pattern of development has not always been along conventional lines. Staff from Winchmore Initially did a contour survey on a 30-acre “guinea pig" block, indicating what soil would have to be shifted to enable the country to be border-dyked. Helped by an irrigation development loan, a 50 horsepower road grader was bought early in 1967 with the intention of carrying out land preparation for irrigation along conventional lines, but it soon became obvious that the grader was not the ideal soil-moving machine on this country. The major part of the preparation of the first 150 acres for irrigation was done by a rubber-tyred farm tractor with a blade on the front—later a crawler tractor was acquired to assist With the tractor dozer working between plough furrows defining the position of future border-dyke banks, it was found that it did the smoothing job down to about three inches from level much more quickly, moving less soil

than the grader and leaving much less country with bare shingle exposed. The cost was also of course much less. The grader finally came in to erect the banks and, when the final levels had been taken, to complete the levelling job. The cost of land preparation, including the race at the head of the borders, with the Newtons doing the job themselves, has ranged from about $6.50 to $8.50 an acre. An instrument for taking levels, used by the Newtons,

consists of an old Bofors gunsight which swivels on what was an old car engine pump, and the driver of the grader has in his cab in front of him a bubble indicating whether the blade is working on the level. An adjustable collar is on the frame from which the blade is slung so that allowances can be made in the future as the blade wears. The Newtons’ authority to use water from the North Ashburton River allows them to take up to 12 cusecs intermittently—say two or three days a week—and another subject of early deliberations was about the sort of races that would carry sufficient quantities of water on this porous country to ensure that there would be enough to cover the borders. The idea of V-type races was discarded in favour of shallow races with low banks because the height of water in narrower races would constitute an erosion

threat on this type of country. The policy then has been to build races some 9ft wide, and even wider races are planned. On the first 30 acres border dyked 6ft wide inrace and border sill structures were installed, but because of the volume of water and the erosive nature of the soil these wooden structures had subsequently to be bulldozed out and replaced by Bft wide concrete structures both in the race and at the head of borders.

The concrete structures have been found to be cheaper as well as more durable than their wooden counterparts which developed cracks. At first some of the concrete work for these structures was done on the site but now it is being cast in the farm yard in multiple lots, so that they can be ready in advance of an area being prepared for watering. A sophistication now being introduced to these structures is to place the abutments or shoulders of both the in-race structures and border sills across the banks. This is to form an obstruction to stock to deter from using the banks as tracks and causing bank erosion. Also, to avoid bank debris falling into the race, the shoulders of the border sills and the shoulders of the in-race structures are being linked by concrete slabs.

Rather oddly, because of the volume of water being i used, quite a lot of silt is t being deposited in the bor- > ders. In view of the better moisture conservation char- ; acteristics of this country when it is covered in this way, it is felt that in future less watering may be 1 needed. s It has been found, how- - ever, that the borders on 1 this country—mainly about t 20 chains long—are rather s too long for adequate water- > ing and would be ideally about 14 chains long.

The shallow race and low bank system has facilitated water being collected again from the bottom of some borders for further irrigation. The first 30-acre block was sown down to a mixture of 31b of white clover, 31b of Montgomery red clover, a bushel of perennial ryegrass and some dogstail, which has not been seen since, and Ijcwt of superphosphate. No lime has been needed as the soil pH has increased since irrigation began. In the 1968-69 season this area carried five ewes and their lambs to the acre in the spring, with the lambs all being fattened by Christmas. The ewes then went on to dry land and the remaining lambs on the place were brought on to the irrigated area, now enlarged to 50 acres, and fattened, bringing the tally of lambs fat-, tened for the season to 903.' Then ewes were also fat-j tened on the same area. Until that year only from 170 to 320 lambs had been fattened in recent seasons on the property, and no ewes at all. In 1968-69 903 lambs and 235 ewes were, fattened and in the most recent season 1334 lambs and 402 ewes were fattened. In the last season after all home-bred lambs had been fattened by early ini March, 252 ewe lambs were I bought in and all but about! 20 or 30 had been fattened; by the time the works) closed. In addition, from) late March to early May for) about six weeks, grazing was provided for 711 North! Canterbury sheep. The flock has been increased to 2100. including j--1834 ewes and 266 hoggets;) and it is expected that by; this time next year another;l 400 ewes will have been) I added. The flock comprises;! both Romneys and Corrie- I dales. A watch is being kept I on how the Corriedales fare I under irrigation conditions I before any changes in the I flock composition are made. I Within a year Mr Newton I expects to be looking at the I possibility of moving in to I cattle. It is intended to go on pre- I paring a further 70 to 100 I acres a year for irrigation I until eventually about 850 I acres can be watered. By I June Of this year the area I that could be watered was I .234 acres. Whereas formerly past- I ures would be about the end of their useful life after only about three years, now the oldest irrigated pactures, which are of about this age,) are showing no signs of de-) terioration and are in fact; improving. They form a striking contrast with adjacent stony, arid country. One of the pleasing features of irrigation has been the measure of control of) grass grub that it appears to give. The Newtons tell the story) of an eight-acre paddock near the homestead that was wild flooded in the first year that they started irrigating. It was very heavily infested

with grubs and at the time the water was put on it attracted masses of. birds of all types. Subsequently this area carried 10 ewes and their lambs to the acre and 75 to 80 lambs were tailed off it. And it has remained free of grubs since. Whereas border areas that have received plenty of water have a thick sole of grass on them and show no signs of grub infestation, there is still some evidence of it at the tail end of long borders whefe the water coverage has been less than adequate. While full of praise for the help that he has received from the Winchmore irrigation research station

in his project, Mr Newton strongly holds the view that more resources should be put at the disposal of the station so that it can cooperate with farmers in ventures like his. Information that is still) lacking in many cases could be accumulated so the station would be able to advise farmers fully about the development of their country, especially if it falls into the category of being rather more difficult than normal. In his case Mr Newton has had to learn often by trial and error because the information was simply not available. He would like to think that in future those undertaking this sort of work could be presented with a blueprint enabling them to avoid having to work on trial and error, with the consequent waste of resources.