A VAST SOURCE OF POWER

Evening Star, Issue 14512, 2 November 1910, Page 5

A VAST SOURCE OF POWER

NOW LIES IDLE WHICH WOULD IRRIGATE CENTRAL OTAGO. “ Central Otago may be made a glorious country, but tho danger is that while we are waiting for great things in the way of expensive schemes we may be neglecting the simple method under the glamor of big proposals which promise large results, hut which will take years to complete, and when completed, will possibly entail such rates to pay interest, on. capital and upkeep as will discount to a largo extent their usefulness.” In these terms Mr F. W. Payne concluded a short preliminary address lo the Otago Institute last night on a simple and inexpensive scheme for irrigating Central Otago economically and quickly by using the energy of river currents at low pressure. —Kawarau and Clutha Rivers. — Mr Payne pointed out that the energy of river currents had been made very little use of in the past, it being generally assumed that the results obtainable were too insignificant to be worth consideration for the development of power. This opinion, he conceded, was well founded on the results obtained by experiment and trial on rivers generally. "But,” he continued, “new factors are brought to bear on. the question, when we come to consider such rivers as tho Kawarau and Clutha, which probably have the most uniformly rapid current of any rivers in the world. A speed of four miles per hour is considered rapid on many rivers, but in these rivors a current as low us four miles is exceptional, six, seven, und eight miles bing common, and even twelve miles per hour being met with in some parts of the gorges. Now, let us consider hero what this means. A speed of fqur miles per hour is, perhaps, hardly worth the cost of harnessing up, but the fact that the energy increases as the cube of the velocities shows that a six-mile current has nearly three and a-half times the energy of the four-mile current. It will thus be seen that this apparently small difference in the current speed constitutes such a difference as to entirely overcome the objections raised; and when wo consider the higher velocities there can no longer be room for doubt that we have right here in Otago a most valuable asset in our rivers, not the less valuable because so tar practically neglected.” —How to Harness the Energy. “Having thus proved the existence of energy worthy of consideration, the next question is: What is the best method of utilising it, and for what purpose? Ihe energy available may lie conveniently expressed as so much per squaiS foot ot cross sectional area of river ; and thus t.ie means adopted must be such as will embrace a considerable area if any large power is required ; and to do tliis effectively the old-fashioned current wheel, with certain modifications and improvements, would appear eminently suited to requirements.” Mr Payne gave an illustration of what might be expected. Nearly two years ago he had designed a pouer plant to work on tho Clutha River at Alexandra, the power obtained lo be utilised in pumping water out of the river into tho dredge paddock of the Alexandra Lead Gold Dredging Company, and also to sluico off the overburden. The conditions wore that the velocity of tho stream was 5.7 miles an hour, the efficiency of the centrifugal pump was 41.7 per cent; and yet under these conditions, with river and current below normal and a centrifugal pump of very low efficiency, the quantity of water discharged was 2.5 cubic feet a second or 2 j heads. Mr Payne had no hesitation in saying that with normal conditions, and by the use of a pump of 70 per cent, efficiency, which reputable makers would guarantee, a result of four iucids could bo obtained, and since the estimated amount of water required for irrigation was one head to 200 acres of iand this quantity would irrigate 800 acres. —Scope and Possibilities. — The lecturer proceeded to define the scops of such power plants in irrigating iand. "Tho chief scope,” ho said, “will be for irrigating the large areas of fiat land contiguous to the river. Tho first cost of this system of obtaining water is v'eiy much less than the average cost of grii.vit.ition schemes, and the upkeep, it Is confidently anticipated, will also be considerably less than that required to maintain long water courses. A further most important feature is tho certainty of a continuous supply. Tho majority of water races arc short of water some time in each vear, and whore crops arc dependent on Ihe water for their developement, a ccesaUrn of supply is liable lo cause heavy lots. The river affords a constant- supply, and is always high in the spring and -ummer; and thus the maximum amount >f power and consequently of water is icallable just when it is most wanted. Another advantage is that it permits of rim conservation of the high-level water® for .he high-level lands, and in considering tho question of irrigation for such a large area as Central Otago tills is a most important feature. Largo tracts of good country exist right away from the river at high levels, which, if irrigated at all, must be supplied by storage of the creeks; nid since the total" amount of such storage ,vill, in all probability, not bo sufficient to irrigate all tho high land available, it would appear that pumping will eventually have to be resorted to lor * tho higher levels unless I lie requirements of the higher levels arc lo bo ignored. Pumping lor irrigation is by no means unknown. The Australian .setJements of Mildura and Roumark depend entirely on water lifted by steam-driven pumps from tho Murray River, and, with ihe system here .suggested, the water can bo lifted at a small fraction of ihe cost of steam. —'Hie Question of Plant.— " In designing plant for utilising the currents of rivers, the question of efficiency in a purely mechanical sense, though im|iorlant, does not claim first attention. The energy being supplied free, it need not greatly concern us whether we use it to the very best mechanical advantage or not. the aim should bo to secure financial efficiency, or the greatest result in power for ,ho ieiisl expense in money. A current wheel with feathering or other refinements of floats would no doubt give greater mechanical efficiency, but if the wheel cost much more than a "wheel of ordinary construction to give out the same power, the refinements are in this case of no use to the owner of the wheel, who will judge Uio value of the plant by tho result he achieves with the money invested. From tho above consideration, I have not so far seriously considered the using of feathering floats, but it is quite conceivable that under certain conditions a feathering wheel would bo advantageous. It could be made smaller in diameter than a fixed-float wheel, which would reduce the weight of tho wheel itself, and also, by increasing the revolutions to attain.same foot speed of float, it would permit of lighter shafting and gearing throughout being used. The reasons for using a largo wheel in preference to a smaller one are the Reduction e* the difference of speed between the insure and outside radii of floats, and the obtaining of a sufficient angle of entrance between float and plane of river surface. The chief losses of efficiency in a current wheel are duo to these two causes.

•‘This paper is only intended as introductory, and I have endeavored to avoid technicalities and statistics; but it is hoped that I have at least proved the claim of tliis source of power to fuller consideration by engineers and by all interested in the development of Central Otago, with which development Dunedin must always be closely associated.”