CAPTURED WATER
SUPPLY FROM MOUNTAIN STREAM
CITY’S AUGMENTATION SCHEME
PROGRESS OF WORKS
Twenty-two miles from Wellington by a round-about route, tucked away between the picturesque bush-clad ranges that rise from the Orongorongo stream, a small dam is rapidly nearing completion, from which, in a few months’ time, the city will be receiving the greater part of its water supply. At this far-away and lonely spot on a small mountain river the babbling water is to be disturbed in its natural course and captured by a weir that will imprison it in large steel pipes and carry it through a two-mile tunnel, till it is at last delivered, after a long journey, into the Karori reservoir.
This big scheme of the City Engineer (Mr. W. H. Morton) for the augmentation of the inadequate water supply of the city sounds simple enough, but it involves many engineering difficulties, which it is costing the ratepayers thousands of pounds to surmount, and the immensity of the contract can only be appreciated upon a visit to the scene of operations.
The boring of the tunnel through the range that divides the Wainuiomata Valley from the Orongorongo, in order that the pipe-line may follow an even grade from end to end, has been referred to in several published articles, but the operations have never been described as viewed from the Wainui side of the big range. By courtesy of the Chief Waterworks Engineer to the City Council (Mr. J. M. Morice), a “Post” reporter was able to make the trip yesterday across the bush-covered hills from the tunnellers’ camp at Wainui and see what is going on on the eastern side, where Mr. Robert Semple and a number of his co-operative workers are steadily eating into the hard rock to meet the remainder of the party, who are boring at the western face.
The journey was made on horseback over the pack track constructed the winter before last by Mr. Semple and seven of his comrades. The going was slow and tedious, for the track is rough, and in places uncomfortably steep both for steed and mount, and it was not until about two hours’ trudging at a walking gait that the four miles and eight chains were covered, and the visitors emerged upon the little camp which is the centre of the operations in the Orongorongo.
The country is much the same as in the Wainui Valley but considerably rougher. The hills rise more steeply from the valleys, but the bush is just as dense and of the same nature. The stream which is being tapped flows immediately below the mouth of the tunnel commenced on this side some months ago. Clustered near the mouth of the opening in the hillside are the miners’ quarters—huts and tents, eating-houses, stables, stores, turbine-house, forge, etc.
The 80-h.p. turbine, which is driven by water from the weir at the point of intake some chains further up the river, serves the triple purpose of operating the air compressor plant for working the drills, the dynamo for the electric lighting system, and the fan for the ventilation of the tunnel.
Across the stream lie the stables, with horses feeding from troughs in the open air, and close by are stacked 21-inch pipes that are being laid through the tunnel—4000 feet of heavy steel pipes, each 24 feet in length. The transportation of these heavy conduits from Wellington is one of the difficulties the engineers have had to contend with. It would be quite impossible to “pack” them across the hill, and the alternative has been adopted of transporting them by motor-lorry over the Waiwetu Hill to the mouth of the Orongorongo, and thence dragging them on wagons drawn by horses up the bed of the Orongorongo from Riddiford’s station to the camp, a distance of about fourteen miles. In places where the bed of the stream is too rough for such means of transport roads have had to be constructed.
Other heavy and cumbersome materials, such as machinery, truck rails, tools, and cement, have to be taken by the same route, but provisions for the camp are delivered regularly by pack horse over the mountain track.
The point at which the Orongorongo stream is dammed is about half a mile above the tunnel. The dam, or weir, which will be finished in a few days, is 75 feet across, and in thickness is 12 feet at the foundations, thinning to 2 feet at the top. Thus caught, the stream water will be diverted into a small chamber and will flow through small holes in the concrete flooring into the 21-inch mains. At present, while work is proceeding at the weir, the water is directed into this chamber by means of a flume, and the turbine near the tunnel is thus driven by water.
A couple of hundred yards below the weir a five-chain tunnel has been bored through comparatively soft rock in order to avoid a detour in the laying of the mains of seventeen chains by following the river bed. With pipes costing 26s 6d per foot landed at Petone station, such a shortening of the distance is fully justified by the saving in expense.
The stream has been tapped at a point sufficiently high—800 feet above sea level—to enable the water to flow by gravitation from the source of supply to the Karori reservoir. The pipes are therefore being laid on a falling grade, which varies at certain stages of the journey citywards.
The laying of the pipes is actually completed from the point of intake to the boring face in the tunnel, and is being carried through as the work advances; the section of pipe in the tunnel serves a very useful purpose in the ventilation of the workings. The big conduits are being used for the same purpose at the other face on the eastern side of the range, and when the boring is finished the line will be immediately connected up.
Then will follow the extension to the Morton dam and on towards the city at a higher level than that followed by the present pipe-line from Wainui. The dam at Orongorongo is at a higher elevation than the Waiwetu Hill—sufficiently high to permit of the water flowing to the Karori reservoir. The pressure will be sufficient to supply all the requirements of Ngaio and Onslow when the new drainage and water scheme is carried out.
So far as the boring operations are concerned, the contract let by the City Council to Mr. Semple is more than half completed, and the contractor expects that his work will be finished soon after next Christmas. Boring into the hard rock is being performed by means of pneumatic drills, and is now proceeding apace. Some time ago Mr. Semple’s men established an Australasian record for such work by penetrating 280 feet in a month. This figure was bettered last month by a foot, and Mr. Semple hopes that this month it will again be increased by about twenty feet.
The length of tunnel to be bored is, roughly, 10,500 feet; of that distance, on 30th April, 2096 feet had been bored from the Orongorongo side and 4042 feet at the Wainui face. Excellent progress has been made on the eastern side, where operations have been in progress only since October last. The progress made in 93 working days during the past four months was 1892 feet—1037 feet at the Orongorongo side and 855 feet at the Wainui side.
The “country” now being worked is dry and hard, and the drills are biting into it splendidly. Mr. Semple’s party consists of 37 men, of whom 19 are at present working on the far side of the range. Below the works on the western side of the hill the Morton dam was found to be in excellent order, banking up a good supply of water; the overflow, however, does not appear as large as is usual at this time of the year.
The water is being utilised for the driving of the turbine which operates the gear in the Wainui tunnel, and the machinery has therefore been erected about half-way between the new upper dam and the reservoir below.
All being well, the big boring contract should be completed by Easter next year. Mr. Semple and Mr. K. M. Barrance, the supervising engineer, mention Easter as the outside date, by which time the mains should be connected up and everything ready so far as the tunnel is concerned. The extension of the big mains to the city and the Karori reservoir is another matter.
