Community Contributed

Mangahao Dams - Diagrams and photos

A collection of images relating to the construction of the Mangahao Power Station - located just outside the township of Shannon. Collected by Bob Ayson, Foxton.

Opening the Mangahao Power Station:

>> Watch silent film of William Fergusson Massey opening the Mangahao Powerhouse on 3 November, 1924. <<

(PLAN OF SCHEME)

This plan of the entire layout of the scheme is displayed on a sign in front of the Mangaore Village Hall. It was erected in 1974 to mark the occasion of the station's 50th anniversary.
	The text below the diagram reads: The comprehensive scheme whereby the capacity of the Mangahao River will be utilised to the full in the generation of electric power is shown clearly in the above plan, which was supplied by the Public Works Department. As has been already pointed out in The Post, the volume of water in the Mangahao is not great, and for that reason it will be necessary to construct the three big reservoirs which are marked, respectively, No.s, 1,2, and 3. These reservoirs, or dams, will be of enormous capacity. The No. 1 Reservoir will have a capacity of 84,402,000 cubic feet, or, roughly, 500,000,000 gallons. The height of the dam will be 85 feet above the level of the stream. The No. 1 Reservoir is on one side of a hill, and the water will be conveyed to No. 3 Reservoir through a tunnel (plainly indicated in the plan) 80 chains long. No. 3 Reservoir, the smallest of all, will have a capacity of 46,014,000 cubic feet, or, roughly, 300,000,000 gallons. These two dams will be completed first, and their completion is essential before further operations can commence. At present the river flows on towards Woodville, but its course will be diverted by means of the tunnel already referred to. As the Mangahao carries very little shingle—it does not erode itself at a very fast rate—it is anticipated that the treatment proposed will not prove difficult. From Reservoir No. 3 the water will be carried by means of a longer tunnel (107 chains in length) to the surge chamber, at which it will enter the pipe lines which will carry it to the power station, 2½ miles from Shannon. Reservoir No. 2 will not be proceeded with until the remainder of the scheme is completed. It will be, in every sense of the word, a storage reservoir, and will have a storage capacity of 106,143,000 cubic feet, or, roughly, 650,000,000 gallons. The height of the dam from the bed of the stream will be 90 feet. The height of the dam at No. 3 Reservoir will be 85 feet. The preliminary work, which is to be taken in hand at once, includes the improvement of the present road, which is shown in the plan as a double line running close to the Tokomaru Stream. This road is, in its present state, quite unsuitable for the conveyance of the necessary constructional material. In addition, the road will have to be extended from a point near where it crosses the Tokomaru to No. 3 Reservoir, thence by a circuitous route to No. 1 Reservoir, and, ultimately, on to No. 2 Reservoir. The tunnelling is, of course, regarded as the most important part of the undertaking, for it will necessitate the employment of experts. However, as far as the longer tunnel is concerned, it will be possible to work from several faces, and that will expedite the work. The inset is a longitudinal sectional plan, the understanding of which calls for a little imagination. Those examining the inset must try to imagine for themselves the three dams in a straight line. The nature of the hills to be tunnelled is plainly shown. But more than that, the inset shows the extent of the drop, which is 900 feet from the surge chamber to the powerhouse, or nearly 1,000 feet from No. 3 Reservoir. The whole scheme will provide for the generation of 24,000 horsepower all the year round, and the estimated cost of it is £438,654.
(PLAN OF POWERHOUSE) The Powerhouse. In the basement of the building are the main pipes and valves, the bus or interconnecting pipe, and on the eastern side, the turbine and generator pits. The main floor contains the turbines and generators on the eastern side, the reactances and low-tension switch-gear in the centre, and the transformers on the west; At the north end is the workshop, and south of the transformer room is the oil store. Both the generator and transformer room are open to the roof, and are equipped with overhead cranes. Above the low-tension switch-gear is the control . room, with offices to the north and the battery to the south. Above this again, is the high-tension floor.
ILLUSTRATIONS
1. Cover: The Mangahao hydro-electric power station, the first of the major power schemes in New Zealand. Built between 1919-24, the station supplied power to all the Southern part of the North Island. The construction work was often difficult, complicated and hazardous, and on its completion it was regard as a triumph of determination and ingenuity. Photo: Godber Collection, The Alexander Turnbull Library.
2. (Night of Tragedy): The carbon monoxide fumes given off from an engine similar to this one, caused the death of seven men in the number two tunnel. The man next to the engine is Alex Grady, a tunneller.	Need photo...
3. The Mangahao River, flowing deep in the heart of the Tararua Ranges. This is how it looked before men and machines invaded this peaceful scene and diverted the waters to provide power and light for industries and homes. Photo: NZED.
4. The hazards of transporting material for the dams by mountain road. Fortunately accidents like this were rare, which is a surprising considering the two ton trucks didn’t have brakes. The road was so narrow in some places that vehicles could only pass at a few wider corners. Logs were placed on some of the sharper bends to prevent drivers backing over a 300 foot drop. Two shifts of drivers transported all the men and material (totalling 140,000 tosn) to the dam sites, night and day in all kinds of weather. Photo: Palmerston North Public Library Collection.
5. (Construction Layout of the Mangahao Dam slim.) Photo: Palmerston North Public Library Collection.
6. The top of the jigway with a truck load of material descending to the Mangahao Valley, 500 feet below. The main camp is situated on the terrace overlooking the river. The big building in the center is the cookhouse capable of seating 140 men. Photo: Palmerston North Public Library Collection.
7. A view of the jigway from across the river. The double -line of tracks climbed the hill at a 45 degree angle, providing the quickest and efficient method of carrying goods to the valley floor. The building at the bottom is the temporary steam and compressor plant. Photo: NZED Collection.
8. The Mangahao Gorge looking upstream, from a level approximately the same height and position of the dam, before the dam was built. Early excavation work-is has started on the left bank. A tramway crossing the bridge, connects the camp with the jigway behind the bank on the right. Photo: NZED Collection.
9. The gorge, looking downstream from a position near the entrance to the number one tunnel. The building emitting steam is the compressor plant. The site for the big dam is just behind the bridge crossing the river. Photo: NZED Collection.
10. Preliminary excavation work for the dam underway. At the bottom of the photo is a test tunnel, driven to determine the quality of the rock. The apparent solid rock wall is no more than a thin shell, concealing the scooped out depression of the old river bed. Photo: NZED Collection.
11. The deep trench on the left bank being excavated for the foundations of the dam. The tower-like building has an electric hauler in the top storey and a cement store below. On the side are bins of sand and rubble. A concrete mixer is in the centre of the photo. Photo: G L Adkin Collection.
12 . The first line of interlocked steel sheet piling being driven to form a coffer dam immediately above the dam site. Another coffer dam of similar construction was made on the downstream side and the space between them was then pumped dry to enable work to proceed on the excavations on the riverbed. Photo: G L Adkin Collection.
13. The inlet end of the bypass tunnel with moulds for the concrete lining being fitted into position. The tunnel entrance is bell-shaped. Photo: G L Adkin Collection.
14. The diversion dam of cemented boulders turning the river into the bypass tunnel, leaving only dead water at the dam site in the gorge. Photo: G L Adkin Collection.
15. Looking across the gorge to the east bank, showing the deep excavation required for the concrete seal, and the concrete wing-walls necessary for strengthening the rockface. G L Adkin Collection.
16. The upstream buttressing and retaining wall of the dam nearing completion. Photo: G L Adkin Collection.
17. Shown here is the method of construction of the buttressing and retaining walls. The concrete from a mixer on the banks on the left is carried to the top of the tower in an elevator bucket and discharged by a chute into the boxing of the upstream wall. The chute on the left leads down to the foundations of the downstream wall. Photo: G L Adkin Collection.
18. Men working on the riverbed foundations protected by the walls of the coffer dam in the background. Photo: NZED Collection.	Photo?
19. One of the many floods which swept through the gorge with devastating affect. It was said that you could see a flood coming around the corner in a fierce, surging wall of water over eight feet high. Here, the swirling waters lap around the base of the compressor building at the bottom of the jigway. Photo; Palmerston North Public Library.
20. Floodwaters almost inundating the suspension bridge carrying the tram tracks across the gorge. Many hours of work was lost due to these "flash" floods which destroyed construction work time after time. Photo: Palmerston North Public Library.
21. A group of men pose outside their huts at the main camp. Over 300 men worked on the dam. The huts were built on terraces cut into the hillside one above the other. Photo: Palmerston North Public Library.	Photo?
21B. Additional photo ...
22. View showing the dam nearing completion, with the chuting [unclear] tower rising high above the crest of the dam. Everything possible at the dam was done w mechanically, and it was the first time in New Zealand that machinery had been used extensively on a major construction scheme.
23. A view of the 40 ft gap in the dam wall prior to being filled in with 3,148 cubic yards of concrete. The job was completed in three weeks.
24. The reason for the gap dramatically illustrated. Floodwaters surge through the gap and pour into the gorge in a raging torrent.
25. The completed dam taken from the gorge floor, with the coffer dam still in position. The automatic regulating gates are on the crest of the dam between the concrete pillars. Photo Alexander Turnbull Library Collection.
26. The dam in operation. The regulating gates (on the left) tilt over automatically when the water level in the reservoir rises too high.
27. The west bank of the Tokomaru Valley showing the excavations for the Tokomaru dam foundations which had to be made deeper than expected owing to the presence of a rubble and clay formation instead of solid rock. Photo: G L Adkin Collection.
28. The Tokomaru River at the dam site showing the auxilliary dam and flume which diverts the river while the concrete foundations are placed in the stream bed. Excavations for the dam are in the foreground and on the left. A rubble dump for concrete making is in the background. Photo: G L Adkin Collection.
29. A general view of work on the Tokomaru dam in the valley. On the right can be seen the dump of clean rubble and the aerial tramlines leading to the top of the rock-crushing plant. In the centre are the excavations for the dam, dumps of waste debris, and the single men's huts. And on the left are the cement stores, dump of boulders, and the aerial tramline with the electric hauler bringing the crushed rock from the crusher to the concrete mixer. Photo: G L Adkin Collection.
30. Horses did a considerable amount of the initial haulage work at Arapeti. But these were replaced by four ton electric storage battery locomotives, like the one seen here outside the engine room and air compressor plant at Arapeti. There were three of these trains and each carried 20 tons of material on a two foot gauge track at about four mph. Light petrol driven locomotives made at the site, using the engine and differential of old Ford cars also operated here. The steel side tip trucks when fully loaded, each held 20 cubic feet of material weighing 30 cwt. Photo: G L Adkin Collection.
31. Excavation for the dam being carried out in the bed of the Tokomaru River. The men are working beneath the flume which carries, the water of the river. Photo G L Adkin Collection.
32. Excavation for the dam on the west bank of the river. The crane is lifting truck-loads of spoil from the excavations under the flume to the tramline above, which leads to the rubble dump. The deep narrow trench for the concrete seal is on the left. The aerial tramline for hauling the crushed rock to the concrete mixer is at the top. The trucks on the tramlines in the foreground are also unloaded by the crane. Photo: G L Adkin Collection.
33. Another view of the excavations on the west bank of the river showing the concrete seal wall built up to ground level, and the "steps" of solid rock on the right on which the main portion of the dam will rest. Photo: G L Adkin Collection.
34. Excavations on the east bank, showing the flume resting on concrete piers, and the deep excavations under the flume completed and temporarily filled with water. Photo: G L Adkin Collection.
35. Construction of the main wall in progress. The building at the top is the rock-crushing plant and concrete mixer. The concrete from the mixer poured down the chute in the centre into the boxing below. The total amount of excavation work required for the dam was 19,667 cubic yards, and the amount of concrete used was 22,262 cubic yards.
35B. The dam wall straddling the valley during the last stages of construction. Equipment litters, the valley floor which will soon disappear under millions of gallons of water. Photo:
36. The Tokomaru dam contains the waters of the reservoir which fills the Arapeti basin. The reservoir contains over three million gallons of water.
37. Visitors on top of the dam viewing the newly formed reservoir.
37B. Top Dam (No. 1).
38. The entrance to number one tunnel from the Arapeti side. The tunnel is 80 chains long and cuts in a straight line through the solid rock to the Mangahao reservoir. Disappearing into the tunnel entrance is a ten inch ventilation pipe. The man standing outside the entrance is George Fern, an electrician.
39. Inside the number one tunnel. This photo was taken by the glare of the tunneler's carbide lamp on the left. On the right are the various pipes providing air, water, and ventilation services to the tunnelers at the face.
40. Two tunnelers working at the face. They are driving rods into the rock so that explosives can be placed into the holes. Certain sections of rock were so hard that blasting gelatine had to be used with the gelignite to blow out the round. Photo: NZED Collection.
41. The Arapeti end of the number two tunnel in which seven men died when gas fumes from a petrol engine poisoned the air in the tunnel. The length of the tunnel is 105 chains and it conveys the water from the Arapeti basin to the surge chamber. Like the number one tunnel, this tunnel is also completely lined with concrete.
42. A group of tunnellers in number two tunnel. The men are, from left: Charley Storey, Alex Grady, Lou Deveroux and Bill Whelan.	Photo to scan ...
43. Tunnelers working at the face. Charges of gelignite are placed in the holes when the rods are withdrawn. Photo: NZED Collection.
44. View looking from the outlet end of number two tunnel where it emerges at the bottom of the surge chamber. The tunnel in the background will connect the surge chamber with the pipeline. Photo: G L Adkin Collection.
45. Construction in progress under the surge chamber showing the head of the pipeline. Photo: G L Adkin Collection.
46. This huge hole is the excavations for the surge chamber. A concrete-carrying bucket or "skip" is hoisted up the mast (in the centre) from a truck on the tramline at the bottom of the surge chamber. It is then poured into the boxing at the required level as the lining of the walls progress. Photo: G L Adkin Collection.
47. The rock-crushing plant and 20 cubic feet concrete mixer at the top of the pipeline discharging liquid concrete to be used in the surge chamber. Photo: G L Adkin Collection.
48. The lining of the surge chamber completed. It was excavated out of solid rock totalling 9,400 cubic yards. The upper portion was worked from the top and the balance, about 7,000 cubic yards, was worked from the tunnel level.
49. Looking down the funnel of the surge chamber to the tunnel at the bottom connecting the number two tunnel with the pipeline. The surge chamber was lined throughout with heavily reinforced concrete, two foot six inches thick at the bottom, tapering to 12 inches thick at the top, the total concrete volume being 1,479 cubic yards.
50. The surge chamber completed and in operation. The purpose of the surge chamber is to maintain an even pressure of water through the pipeline to the turbines.
51. The top of the pipeline with the rock-crushing plant and concrete mixer on the left. In the centre is the dump of rubble from the tunnel leading into the surge chamber. And in the right foreground is the hauler shed for the tramline which runs beside the pipeline. Photo: G L Adkin Collection.	Photo?
52. A general view of the construction work beginning on the powerhouse. On the right are sections of pipe for the pipeline. Photo: G L Adkin Collection.
53. Loading a pipe on to a truck ready for hauling to position on the pipeline bed. The pipes are of riveted steel and were supplied and erected by the Dunedin Engineering and Steel Company. Photo: G 1 Adkin Collection.
56. The first steep gradient of the pipeline showing the four rows of pipe (3ft 6in in diameter) being fitted together. The huge concrete anchor block at the foot of the pipeline is in the foreground. Photo: G L Adkin Collection.	Photo?
57. Fitting the pipes together by using "jacks" and powerful screw tackle before they are riveted. The formation of the pipeline involved an excavation of 23,000 cubic yards. No mechanical machines were used owing to the steep nature of the country. There was an additional excavation for the 12 massive anchor blocks of 2,405 cubic yards. The total cost of these anchor blocks was 9,135 pounds. A cable tram was considered the most practical way of handling the 10,000 tons of material for construction purposes. It was operated by a 100 hp electric winch situated at the top of the pipeline. The tram had a three foot six inch wheelbase and ram operated at 200 feet per minute with a maximum load of five tons. The pipeline had 12 changes in grade and five in direction, operating over a rise of 800 feet in a distance of 3,600 feet. Photo: G L Adkin.
58. View of the pipeline under construction where it enters the powerhouse. The pipes are being set in reinforced concrete. The three smaller cross pipes carry the water of the Mangatangi stream. Inside the powerhouse the main pipes, bus-pipes and valves, are so arranged that any pipe or turbine may be isolated for repair without interfering with the others. Photo: G L Adkin Collection.
59. The powerhouse under construction. Here work has progressed to the level of the travelling-crane floor. On the right is the elevator mast with the concrete tipping bucket (skip) and the chute discharging the concrete. In the background is the pipeline under construction. Photo: G L Adkin Collection.
60. The concreting of the travelling-crane floor in progress. The liquid concrete discharged from the chute is worked in between the lattice of steel bay reinforcing, and smoothed off with "floats" and left to harden. Photo: G L Adkin Collection.
61. The completed building. Below the road on the right is the tailrace of the Mangaore stream. Photo: NZED Collection.
62. The high tension switching gear on the roof of the powerhouse. From here, the power is fed on a 110,000 volt line to the distributing authorities who transform it down to 11,1000 volts.
63. The Pelton Wheel turbine being unloaded at the Shannon Railway Station after its arrival from the makers, Metropolitan Vickers, of England.
64. The turbine starts on its journey to the powerhouse, pulled by two traction engines.
65. One of the 10,000 volt transformers being towed along the road to the powerhouse by a traction engine. All the equipment required for the station and sub-stations was of English design and manufacture. Photo: NZED Collection.
66. One of the pelton wheel turbines being installed in the powerhouse. There were are five of these machines, th ree being designed for a maximum output of 8000 hp and two for 4000 hp, Both sets of turbines are identical in size and both operate at 375 rpm. Each machine weighs 30 tons. The larger machines have two nozzles directing the water on to the buckets and the smaller machines, one nozzle. A valve inside the pipe nozzle automatically opens and closes according to the demand for power. Photo: Alexander Turnbull Library Collection.
67. The line of generators coupled to the pelton wheels in the powerhouse. Three of the alternating current generators produced 6000 KVA and the two smaller generators ' produced 3000 KVA. Photo: Alexander Turnbull Library Collection.
68. The main control room in the powerhouse. The low tension and direct current switchboards are on either side of the main control panel in the centre. Watt meters and temperature indicators are mounted on the logging desk on the left. Operating instructions were given to the turbine room by ship's telegraph instruments. Photo: Alexander Turnbull Library Collection.
68B. Additional photo?
69. A power line gang laying out hardwood poles (weight 32 cwt, length 52 feet) in paddocks near Levin, for the main transmission line from Mangahao to Wellington. Photo: G L Adkin Collection.
70. The method of erecting one of the big "double" poles near Levin. The butt of the pole is placed in position over the hole and the lift is made by means of a portable derrick. Photo: G L Adkin Collection.
71. The partially lifted pole is held by spikes as the butt of the pole slides into the hole down a strip of concave sheet iron. The final lift is made by using sheer legs when the pole has reached a height too great for the effective use of the crane. Photo: G L Adkin Collection.
72. A crowd gathers at the Shannon railway station on opening day to greet the special train from Wellington bearing the Prime Minister, Mr W F Massey, and other official guests. Photo: NZED Collection.	Photo?
73. The scene outside the powerhouse on November 3, 1924, as guests present their speeches marking the official opening of the power scheme. Photo: Alexander Turnbull Library Collection.

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