The New Zealand Railways Magazine, Volume 2, Issue 4 (August 1, 1927)
Hydro-Electricity. — The Arapuni Scheme
The following information may be welcome not only to those interested in hydro-electric schemes, but also to railwaymen as revealing what such an undertaking means in the way of extra haulage and freights.
Six years ago, Arapuni was known to the residents of Putaruru as a pleasant picnic spot 8 1/2 miles distant on the Waikato River, the flowing of which through the Arapuni Gorge situated amidst beautiful native bush, afforded a sight of great grandeur.
The road from Putaruru, although fair in summer, was quickly affected by any serious rainfall.
To-day, Arapuniis approached by a splendid metalled road. It is a township of over 500 people, and has one school and hospital, two churches, an amusement hall, tennis courts and an athletic field, whilst modern bungalows house the respective staffs of the contractors (Sir W. G. Armstrong Whitworth Co.), and the Public Works Department (which in addition has cottages for the married workers, and barracks for the single men). All the buildings mentioned are fitted with electric light.
On the acceptance of the tender of the Sir W. G. Armstrong Whitworth Co., very careful consideration had to be given not only to the laying out of the big scheme, but also to the method of getting the large quantities of cement, stores, plant and machinery to the scene of operations.
It was estimated that the following quantities of material would be required for the job:-
26,000 tons of cement.
4,000 tons machinery.
500 tons plant.
5,000 tons of other stores
To date, over 24,000 tons of the above materials have been delivered.
The readiness with which the conversion of rolling stock was carried out says much for the capacity of the Railway Department to provide special facilities for special classes of traffic offering.
The smaller cases and castings are unloaded from the railway wagons by a 10-ton steam crane, and the larger cases under a set of sheer legs of a 30-ton capacity, being then conveyed to Arapuni by a road specially metalled for heavy transport.
The 22-ton cases are placed on a 30-ton trailer and drawn by traction engine, or, as in recent instances, by three motor lorries coupled.
The consignments of heavy and valuable machinery require the most careful handling during the time they are on rail, and it is gratifying to observe that appreciation has been expressed that all packages have been delivered expeditiously and without damage by the Railway Department.
A glance at the illustrations will convey to the reader's mind a good idea of the dimensions of the scheme, viz., dam, lake, Waikato River, headrace, spillway weir, overflow channel tailrace, penstock tunnels, diversion tunnel, ropeway, quarry, suspension bridge, power house building, turbines, generators, and transformers.
The visitor will find permission given readily by the Company to see over the works.
Of outstanding interest is the main dam, rising 155 feet above the present river level, with a depth of foundation 30 feet below the river bed, and having a maximum thickness at the base of the dam of 171.5 ft., and strengthened by an eastern cut off wall 110 feet in length by 5 ft. in thickness, and a western cut off wall 50 feet in length by 5 ft. in thickness. The dam and the cut off wall combined contain 95,000 cubic yards of concrete and have a total weight of 155,000 tons.
The diversion tunnel which is now completed and carrying the flow of the Waikato River during the construction of the dam is 720 feet long, with a diameter of 24 feet.
This tunnel, on completion of the dam, will be partially closed to regulate the flow of the river to maintain the Hora Hora Hydro Electric Works (5 miles lower down stream) in operation, whilst the lake is filling, after which the tunnel will be completely closed by two sluice valves.
It is estimated that on completion of the dam, and with the diversion tunnel partially closed, seventeen days will be required for the Waikato River to form a lake 18 miles long, with an area of 5 1/3 square miles and an average width of one-third of a mile.
A few words on the metal supply for concrete work might be of interest by way of conclusion.
The metal is obtained from Muku, nine miles up river from Arapuni, and is conveyed to the dam on a ropeway of 3 1/4 inch circumference, fitted with 375 buckets, each with a capacity of 8 cwt., and travelling at the rate of 4 3/4 miles per hour. The ropeway delivers 40 tons of crushed stone per hour. The weight of the rope is 75 tons, and the driving power is provided by two 60 h. p. motors.
Chance will not do the work; chance sends the breeze;
But if the pilot slumber at the helm,
The very wind that wafts us towards the port
May dash us on the shelves:
The steersman's part is vigilance, blow it rough or smooth.”