WATER FOR THIRSTY LAND

Evening Post, Volume CXXXIX, Issue 147, 23 June 1945, Page 11

WATER FOR THIRSTY LAND

IRRIGATION FIRST, POWER SECOND

''Population cannot expand faster than the rate at which productive and congenial employment become/ available1.. I* have, always been impressed with the advantages which irrigation; off ers< in this irespect, especially in the open spaces of Canterbury and Otago.! When it is possible, as in this instance, to generate electric power as "well,' a double blessing is conferred on the land."—So wrofe the Minister of Works (Mr. Semple) in a foreword to an illustrated booklet, "Water Put to Work, for Power, for Irrigation," which tells in informative detail the interesting story of the at-last-ftilfilled hope of the,first Canterbury Plains settlers to have carried to their too dry farm lands the plentiful water that flows in Canterbury rivers. The dual purpose development is but a small irrigation project in comparison with great undertakings overseas, but it holds great promise for greater productivity and closer settlement for a large expanse of ,farm lands where for thirty years production and population have remained practically stationary. It is really one of the most spectacular water and power developments in the Dominion.

For all its physical limitations, of comparatively few square miles and population, New Zealand has a range of hydro-power developments as. wide and as different as any country in the world. Each, hydro development is j different from the next. Coleridge— the first New Zealand, hydro station— J draws its water irom' underneath1 the lake bed; Mangahao's power house draws water from a river two valleys removed;'* the ,Arapuni generators are in a deep, rocky gorge from which the Waikato has been diverted to flow high above along an ancient river course, unused by Nature for untold years; Waikare uses water from Lake Waikaremoana twice over, and is to use it thrice when the scheme is com-, plete; Waitaki's huge water volume falls but 70 feet to the turbines; Cobb's ! small flow falls 1800 feet. Now there , is Highbank, in Mid-Canterbury, newest of the hydro family, declared open and under way last week by Mr. Semple; it; is furthest removed from other engineering methods of guiding and transforming the power of flowing water into electrical energy, for its single unit of 25,000 kilowatt (28,000 k.v.a,) capacity, is driven by water taken from the Rangitata River and brought 42 miles across the Canterbury Plains to the power station in the bed of the R'akaia River. It is different from all the other New Zea- ; land hydro developments, too, because though a 25,000 k.w. station is a major development — considerably ■greater than Mangahao—the power side of the Rangitata-Rakaia diversion is of secondary importance to the water side, for this is ifie Dominion's first great scale irrigation undertaking. When fully developed it will supply water in plenty to nearly half a million acres of fertile but normally too dry farmlands in Mid-Canterbtiry.' The farms will have, first -call upon the. water, the power station will run after, they are satisfied. , , , •. , „„,.„ Mid-Canterbury .land has always been thirsty. Irrigation was talked: over by the first plains settlers^and sixty-five years ago, when settlement Sas still sparse, they moved from discussion to action, and there was started a water race scheme .to carry water for stock, which grew irj, miles of race to over 2000. That was a great work for a very young Canterbury, but the land remained too dry In .top many seasons. Plan upon plan for - legation came forward from the eighties onwards, getting as far as detailed estimates in 1900. Twelve years ago much more detailed survey work than had been carried out earlier was commenced, and with that wide topographic .survey, went scientific soil surveys, accurate gauging of river flows, soil moisture measurements, and a recording, district by district, of humidity, rainfall, wind, and the rest of the meteorologist's interests. Irrigation was to be planned upon accurate data, positive facts. - :: " "p- ' ■/: - ' WITH HEAVY MACHINERY. Stout as the early settlers were, could they with hand tools and the limited finance then possible, have carried out so immense a constructional job as this has turned out to be? Picks, shovels, and drags would have done the work, but in many, many years. Bulldozers, carry-alls, and canal cutters of special design cut the work hours by a hundred, until, with the main canal finished, the war called a halt to continued fast progress. The main construction is through, but thereis still a great deal to be done for full development. Until the war slowed down the all-over progress this was another example of. the power of modern dirt-shifting plant to get through heavy work. It was a typical Bob Semple job" of cutting canals,, taming the Rangitata at the intake point, and carrying an artificial river underneath rivers In the excavation and the building of the walls of .the maini race alone 5,000,000 cubic yards of earth and stone were handled. FALL OF THE PLAINS. The "dead level1' Canterbury Plains are not level. They, have able fall towards the sea, and at that section the bed of the Rakaia JRrver is well below the bed of the Rangitata, so that the intake in the Rangitata gorge is almost 400 feet above the powerhouse in the bed of the Rakaia River. Forty-odd feet of this fall is used to give a smooth, slow flow along the main race, and the rest in the final plunge (342 feet) by a single penstock to the turbo-generator. At the top this fine large water pipe is of reinforced concrete, 11 feet in diameter; lower it is of steel, 9 feet in diameter. ' i The race is a great channel, wita stopbanks well above ground leySl. At the bottom it is 25 feet wide^nd at the top of the sloping siJ^To muoh wider. It will normally carry a depth of 9ft 6in of water, more than enough in width and depth for canal transport, were it not for the drops and syphons that block this crosscountry waterway at several points, i There are three artificial waterfalls to dispose of surplus head and to slow down the flow, to prevent damage to the race. The syphon^, and "by-washes" are much more interest-

ing features. Running" west to east, the race crosses two rivers, the Hinds and the Ashburton (two branches) between the Rangitata and the Rakaia. Below these two rivers the race dives through . huge concrete pipe syphons. A much' larger syphon, a mile and a half long, tarries the water past a patch of rougher and unstable country •at Surrey Hills. These are the pipes which made . good news photographs a year or *two ago, with a car and a six-foot ■ Minister inside with space to spare after that! The Surrey Hills syphon pipes are 12 feet in internal and • each piece weighs 28 tons. There are lesser syphons where other streams cross the line of the race. .

Check-gate and. by-wash safeguards pour away excess water to stream beds along the race route; The mechanism controlling these and the gates of the Rangitata intake is "tele-controlled" from the Methven Irrigation Office. Telephone and signal lines are connected to all important structures, and the racemen will communicate with each other by telephones at strategic points. From the trunk race main branches set out across and up and down country; from these sub-branches set out again; and from sub-branches," farm branches divide. It will be some years probably before anything like that complete network of main, sub, and farm branches' is complete, for war conditions willfor some time continue to hinder progress. THE ECONOMICS OF FERTILITY. The majority of the Mid-Canterbury farmers are convinced. They wait for the water, though it will, cost money, and the preparation of the farm for efficient irrigation will cost more. It is in part to convince those who remain unconvinced that demonstration areas, which had an-important place in investigation and field research, are maintained. That. productivity will be-very remarkably increased appears quite established. Trials in a 47-acre block over seven- years have increased • the carrying capacity from one sheep an acre to six. Irrigation cost £205 (including interest on capital expenditure and for "levelling, waterways, etc.), but the increased returns consequent upon irrigation were £532, giving a net profit of £327 a year. That was but one of the trials with varying returns, in added productivity. MORE FARMS, MORE PEOPLE. The trunk race will carry .a fairsized river, 1000 cubic feet of water a second—enough to irrigate 8000 acres of grassland in a day, and day after day, over thirsty plains and farmis in dry summer weather. Mr. Semple sees closer settlement ahead when the scheme is fully developed and availed of, from 1800 to 8000 farmers, from 18,000 :to 80,000 of population (farmers and townspeople), and a greatly-increased stock and all-round productivity. He is a * man of tremendous, enthusiasms and of his greater works most have gone well. Putting water to work on the low-rainfall Canterbury farm lands, and the excess to the generation of electrical power, is his present enthusiasm. It, too, promises well. THE HIGHBANK STATION. The Highbank -hydro station, though an important addition to the .South: Island's power pool, is, then, but the lesser part of this irrigation-power undertaking. It will be linked with the main power system and will'run at its fullest output when the power demand is greatest and ,the irrigation demand lowest. September to April will be the irrigation season: April to September the power months. The name • "Highbank" is properly descriptive, "high" .meaning, very, high, for the Rakaia is far below the plain at this point, and the water takes, a 340-foot plunge over the river cliff to the single turbo-generator. This was. made by the English Electric Company and is the largest single generating unit in the Dominion. Highbank has had its troubles. A large part of the heavy equipment went down at sea, lost by enemy action, and was replaced by the makers under all of wartime difficulties of manufacture and of transport. The replacements travelled far and unusually, thousands of miles off normal shipping routes to reach New Zealand finally. At the beginning of this year phenomenal rainstorms in Canterbury almost' ended Highbank,* but catastrophe was averted when flood waters,, threatening the penstock structure and the power house itself, were diverted by the extraordinary endeavours of the station staff. Such damage was done that the station staff settlement was overwhelmed by« a landslide, and the approach road down the river-bank cliff ceased to be. Six months were needed to repair the flood damage and provide safeguards against any likely flood troubles in the future.