Overview
Tues. May. 1.
My 21st visit to Mangahao Hydro-electric Works. A perfectly fine day, sky cloudless, white frost + no wind. Up at 5.15am – Maud turned out + got me a good breakfast. Left on bike at 6.15. Makurerua Swamp + low-lying country round to Lake Horowhenua under a ground fog, the Ruahine Ridge + Ruapehu clear cut on northern horizon. Passe Shannon at 7.15 – powerhouse site as men commenced work – some of the heavy iron pipes for the Pipe Line are now on the spot + men were starting laying them in position. Reached Mangatangi Ford at 7.45 + left bike in bushes. Took hill route + left road at 8.am – reached “timber tram” saddle at 8.30 – the tiny pointed cone of Ngauruhoe was visible over the north-east
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shoulder of Ruapehu – magnificent panorama of the West Central Tararua peaks + the ridges to the north of them, absolutely free of cloud + clear cut in morning light. Descended to Arapete Camp (8.45). Near entrance of Tunnel No 2 took 1/4pl[ate]. photo (1) of stack of curious drain pipes (made of clean rubble concrete) evidently to be used for drainage purposes in this Tunnel. 1/4pl. (2) of engine shed + elec[tric]. locomotive + truck trains in front. Ascended to top of the three-storey rock-crushing plant which was working, the resultant crushed rock being hauled in trucks up the inclined tramline leading to the Tokomaru dam-trench. The concreting of the bottom of the very deep western part of the dam trench has been commenced, [rig.?] the “concrete seal”which cuts the deep rubble deposit here. At the middle part of the dam-trench a large number of men were at work – some excavating in the bed of the Tokomaru River underneath the flume which now carries the water of the river from the auxiliary dam to the down-stream edge of the dam-trench (1/2pl. photo (3) of men excavating under the flume); others taking delivery of trucks of spoil lifted by means of the rotary crane from the bed of the Tokomaru River
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to one of the “levels” on the left bank; while a third gang pushed the loaded trucks along a tramline to a discard dump downstream. 1/2pl. (4) of the excavations on the left bank showing crane in operation, viewed from right bank, + 1/2pl. (5) of same from left bank. Made the aquaintance of the new assistant engineer, Mr. F.W. Lindup, who replaces the late Mr. Miller, and the question of the formation at this dam-site coming up, he disclosed some new + surprising facts which completely upset my recently arrived at conclusion (see notes, Nov. 23–1922) in this connection. Solid rock occurs in the bed of the Tokomaru + on its right bank at a slight depth. On the left bank there is a thick deposit of angular rubble and pug which continues down to a certain level, [rig.?] some 15ft. or 20ft. above the river-bed. At the [eastern?] end of the base of the rubble deposit, the bed-rock rises at a very steep angle to within 30ft. of the ground surface at a spot under the western end of the cement store nearest to the big cookhouses. Immediately across the servie road from the cement store referred to + at a distance of only some 6 yds [yards] or 8yds., a shaft has lately been sunk to further test the “ground”. This shaft had to be sunk
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to the extraordinary depth of 147ft. (i.e. about 20ft. below level of Tokomaru River on line of dam) before bed-rock was reached + as it passed in its lower levels through hard water-worn boulders it seems certain that an old river-channel occurs here. That the bedrock varies in depth in the space of (less than 1 ½ chns) a few yards from 30ft. to 147 ft., seems to indicate that the eastern side of this old river channel has a slope of extraordinary steepness. These unexpected features appear to have been masked by the rubble and pug deposits of an adjacent lateral stream and their discovery at this juncture is a most unpleasant surprise for the engineers. Mr. Lindup who has shown considerable acumen in connection with the discovery of this old river-channel, has explored the gully of the stream that probably laid down the rubble deposit + now drains into Tokomaru some distance below the dam-site, and was successful in finding a mass of river gravel + boulders in the gully side, though solid rock occurs in the bed of the gully a little further down. This bed rock is at a level of only 5ft. below the bottom of the 147ft. shaft showing that the gradient of the old river-channel was very slight. Another point is
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that a deposit of boulders of red jasperiod rock + of flinty greywacke was struck in the cutting at th entrance of Tunnel No2. + this spot is in alignment with the two occurences of similar nature just discovered. If this old channel is the primary old (Tertiary) cause of the Tokomaru River, the river must have made a very big sharp loop at this place. Also its early Pleistocene + later history must have been similar to that of the Mangahao at No1 Gorge. Tests are now to be made to ascertain the permiability of this olf channel as if there is a big soakeg of water along it, it will constitue a danger spot + the concrete seal in the rubble deposit on the left bank of the Tokomaru, will have to be extended for an, at present, unknown distance westward. At the request of a workman named P. Dixon I consented to photograph a group of the men employed here, + they assembled, for one of the 5-minute [spill-on?] allowed, on the rock steps in the trenvh bottom on right bank (1/2pl. (6)) Left Tokomaru dam-site at 10.15 and walked up gully of Tokomaru to outlet end of Tunnel No1., arriving at 10.24, + went through this tunnel, which is now completely pierced, to the Mangahao River. From its outlet for about one-third of its length the concrete
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lining is finished, + for some distance further the floor is lines, men being busy at this job at date. The reamined is naked rock except for a few timbered portions. In only one place was any quantity of water leaking from the rook. Got through the tunnel in 27 minutes lighting my way with electric torch. The most striking evidence of progress at No1Gorge was the upstm [upstream] “buttressing” wall built along the crest of the rock rib. This is now nearly finished, and rises to a considerable height (about 50ft.) though only 2ft. wide at the top. 1/2pl. (7) of this wall from point on left bank upstream. 1/4pl. (8) of same from near eastern end of suspension bridge. 1/2pl. (9) of same looking upstream from end of trench of down-stream “buttressing” wall. Met Mr. Copper who informed me that the upstream “buttressing” wall will act less as a buttress to the big dam than as a retaining wall for debris which will be piled up against the dam itself. On top of the high-level terrace I found the electric rotary crane lifting “spoil” out of the deep trench which is now down to a depth of about 90ft. The concrete-mixer (1/4pl. photo (10) was also working at top speed supplying liquid concrete to the “buttressing” wall. Now
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that the wall is well up + at a higher level than the mixer, an elevator has been installed which travels up a great vertical beam by means of a cable operated by an electric winch. The concrete runs from the mixer down a shute to the base of the vertical beam, is then tipped into the elevator bucket, which ascends + on reaching the top strikes an iron frame which automatically brings up a coupler connection + tips the contents of the elevator bucket down another shute leading to the crest of the “buttress” wall. Ascended to crest of “buttress + took 1/4pl. photo (11) of men shovelling in the concrete. Mr. Cooper kindly invited me to dinner + detailed one of the foremen, a mechanis named J. Tennant, to see me provided for. After dinner Tennant took me to his hut and showed me a fine series of photos of the works + of Ruapehu, Egmont, +c. Returning to the deep trench, took 1/2pl. (12) showing crane at work, +c looking across high-level terrace + gorge from hillside above former. Visited the upper storey of the tpwer-like hauler + cement stone building + saw trucks of rubble for conrete work being hauled up the inclined tram-line from the lower level. 1/4pl. (13) of men tipping truck of rubble into storage bins. Visited the upper
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end of the By-pass Tunnel where the moulds for concreting the tunnel entrance are being put in position (1/2pl. photo (14)) – this tunnel opens out to a larger size at its entrance after the fashion of a bell. A third coffer dam of wood piling has been erected + if no more devastating floods occur this part of the work should soon be completed. The temporary sloping adit of the By-pass Tunnel is now blocked up with the concrete lining of the tunnel. Left No1 Gorge at 1.25 – 1/4pl. photo (15) of the “simple life at Hilltop Camp” – i.e. one of the homes of the married men employed at No1 Gorge. Reached Arapete via Service road at 2.15. 1/2pl. photo (16) of Arapete-Tokomaru works from part way up old timber tramline. Ascended to saddle 2.30 – Tokomaru Valley Rd. [Road] 2.47 – picked up bike at Mangatangi Ford 3.5. Stopped at Hydro-electric Powerhouse + took 1/2pl. (17) of men placing iron bars for reinforced concrete floor (transformer floor) + 1/2pl (18) of the power water-pipes in southern end of Powerhouse ready to be connected up with the Pipe Line. Men are now commencing the laying of the pipes on the Pipe Line bed. Left Powerhouse 3.45 + reached Woodside at 5.20pm after a very successful outing the weather remaining perfect right through.