Part 29 (2/2)
[Footnote b: On this pa.s.sage the Hydraulic Engineer notes that, in 1891, a bill was introduced into Parliament by Sir Thomas McIlwraith for controlling the artesian water supply, and pa.s.sed through the a.s.sembly, but was rejected by the Council. Since then no action in that direction has been taken.]
IRRIGATION BY BORES.
The same report contains an interesting article on irrigation.
It points out that at the beginning of 1892 there were only 200 irrigators among the land cultivators of the colony, and that the area irrigated was only 5,000 acres. It was believed that in the last year the amount of land so fertilised had largely increased. Many of the plants and distributing apparatus were of a most primitive kind.
”Some are expensive, others badly erected, and not a few are of a type ill-adapted to the object in view.”
The report goes on to discuss the probability or otherwise of water in sufficient quant.i.ties for irrigation being obtainable by conservation.
In summarising his argument the Hydraulic Engineer says, ”Looking at the question broadly, I am much disposed to regard the possibilities of a sufficiently abundant supply of water being obtained for irrigation, especially for land in small areas devoted to intense culture, as of considerable promise.” He then urges the inadequacy of artesian wells for the irrigation of large areas, pointing out, among other things, that the entire discharge of the wells then flowing in Queensland would suffice to irrigate only 219 square miles to a depth of 1 ft. He thinks that in Queensland we shall have to depend upon ”natural” water for irrigation purposes.
A VALUABLE MAP--376,832 SQUARE MILES IN ARTESIA.
A new feature in the 1893 report was the map giving information as to (1) artesian bores applied for, (2) under contract, (3) in progress, and (4) completed. It showed that out of a total of 668,497 square miles of the ”Rolling Downs Formation” (Lower Cretaceous) no less than 376,832 square miles, chiefly in the arid west, was likely to be water-bearing. This estimate, it may be noted, has been very slightly reduced of late, but the scope for exploration in water-finding seems still great in Western Queensland. The report alludes to the success attained in the Queensland manufacture of well-boring machinery. All the plant used, the wire rope alone excepted, was manufactured in the colony, where improvements had been made in the originally imported article. Yet it is admitted that the apparatus used was ”not a perfectly scientific one, because it does not produce a core by means of which the nature of the strata and the angle and direction of the dip can be fully ascertained.” Queensland yellow-wood (_Flindersia Oxleyana_) had quite replaced American timber in the manufacture of drilling poles.
[Ill.u.s.tration: SCENE ON LOGAN RIVER, SOUTH QUEENSLAND]
EFFECT OF GOOD SEASONS.
In closing, the Hydraulic Engineer reports that the succession of good seasons experienced (years 1890-93), and the abundance of water and gra.s.s resulting, has occasioned much inattention to water conservation, and he also expresses regret that financial exigencies have compelled the dispensing with some valued members of his staff.
The article is ill.u.s.trated by diagrams, and the studious reader will peruse it with profit.
THE SOURCE OF ARTESIAN WATER.
In his report for 1st November, 1894, the Hydraulic Engineer recurs to the source of artesian water. He regrets that very little can be added to the previous a.s.sumption that it lies in the outcrops of the porous beds of the Lower Cretaceous formation on the western slope of the coast range; and he urges the necessity of acc.u.mulating facts relating to the bores already sunk, and complains that some owners neglect to give the department the information sought. He urges that legislation should make the furnis.h.i.+ng of statistical matter of this kind compulsory. He doubts whether, in the absence of information as to the precise geological conditions subsisting beneath the surface, a map of Queensland can ever be prepared showing with certainty where artesian water can be found; but much may be done by acc.u.mulating accurate information with respect to the sinking of bores, nature of strata pa.s.sed through, amount and pressure of flow, temperature of water, and depth beneath the surface whence obtained in each case. The map issued by the Geological Department would show the water-bearing areas, which means the formation in which water may be expected to be found; but bores can only be put down with reasonable certainty when the entire western country has been prospected.
THE LIFE OF ARTESIAN WELLS.
The life of an artesian well with a permanent spring, says the report, is limited by the durability of the casing. The corrosive action of some water is much greater than others; but there should be no difficulty in renewing the casing when necessary. It has often been discovered that an interruption of the flow, or its serious diminution, is the result of worn-out casing. So much is this the case that there is still controversy as to whether there is any general diminution in the supply consequent upon continuous waste.
ARTESIAN WATER POWER.
The report then discusses the question of using artesian water for power in the industries. The Hydraulic Engineer points out that of the total horse-power used in the United States at that time about 395 per cent. was hydrodynamic. Artesian water, he says, can be applied to driving all kinds of machinery, ”from a sewing machine or a cream separator to a saw or flour mill; and for fire-extinguis.h.i.+ng it is most excellent.” He therefore recommends the employment in Western Queensland of turbines and Pelton wheel motors for sheep-shearing, electric lighting, and other kinds of machinery used there, pointing out that the horse-power available was--At Blackall, 804; at Cunnamulla, 4153; at Charleville, 12341; and at Thargomindah, 6351.[c] He further recommends the utilisation of the artesian supply for street mains, a suggestion since carried out with great public advantage in several western towns. While Mr. Henderson doubts the utility of artesian water for irrigation, he says that, generally speaking, it is quite as valuable as that from town mains, rivers, and falls for developing power. The aggregate area to date in which precious artesian water has been found in Queensland is 117,000 square miles, and he feels that this area would be rapidly enlarged by exploration by both Government and private borings. The shallowest completed flowing well in Queensland at that date was 60 ft., and the deepest 3,630 ft.; the average depth so far as known to the department was 1,289 ft.
[Footnote c: Mr. Henderson notes that these horse-powers have since been very much reduced.]
STATIC PRESSURE AND HYDRAULIC PRESSURE.
Explaining why the volume flowing from a well does not depend upon the diameter of the ”static” pressure of the water, Mr. Henderson says that the flow depends princ.i.p.ally upon the relative alt.i.tudes of the outcrops of the water-bearing beds, and of the mouth of the bore or well, and upon the character and texture of the porous beds from which the well derives its supply. The static pressure is ascertained by stopping the flow by artificial means, when the pressure generally rises, sometimes quickly, at other times slowly, until it reaches a maximum. But when the well is again opened it will be found that the static pressure has been more or less reduced by friction. This reduced pressure is called the ”hydraulic.” The hydraulic pressure can never exceed the static pressure; nor can the volume of water flowing from an artesian well be ascertained by its pressure, or the height to which the water may rise over the top of the casing, any more than the pressure can be ascertained by knowing its volume.[d]
In the same report is announced the striking at Winton, at a depth of 3,235 ft. of a supply amounting to 100,000 gallons a day, at a temperature of 140 degrees. It was determined to continue sinking under a new contract.
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