Overview
Mon. Jan. 14.
My 30th visit to Mangahao Hydro-electric Works. Up at 5.am, milked + breakfasted + left on bike at 7:30 for the Powerhouse + Pipe Line. Passed Shannon at 8:25 + reached Powerhouse 8:45. Had aneroid with me on this occasion to determine altitudes of the various changes in gradient of the Pipe Line bed, which consists of a series of alternate “steeps” + “flats”. – 7 of the former + 5 of the latter. Set aneroid by the datum of the big anchor block alongside Powerhouse + proceeded up Pipe Line taking readings at each change of gradient. Immediately above the main anchor block an oval man-hole has been cut in each of the four 3ft. pipes + the aperture fitted with a stopper of similar pattern to those in the pipes alongside the main valves within the powerhouse. On the “1st steep”, 1st “flat” + 2nd “steep” (gradients) the four lines of pipes are complete except for the joining up of one length of pipe in each case + for some work on the foundations on which they rest. On the 2nd “flat” the lines of pipes have now been extended over the greater part of this gradient – 1/4pl. photo (1) –
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and rivetting is in progress – 1/4pl. photo (2) Anchor Blocks No2. No3 + No4 are now finished + the boxing has been removed. The vertical (re-entrant) angle at the foot of the 3rd “steep” is the spot where the two lines of pipes which are to form the upper part of the Pipe Line, branch into the four pipes of the lower part, + the pair of tapering bifarcated pipes at the junction of the two sections (upper + lower) have been placed in position but not yet set in concrete. 1/2pl. (3) of the bifarcated pipes 1/4pl. (4) another view of same. The angle pipes at each end of the 3rd “flat” are also in position but not set in concrete. On the 3rd + 4th “steeps” the two lines of pipes are laid out ready to be placed in alignment + on the latter gradient the work of jacking them + fitting them in position is now in progress – 1/4pl. (5). On reaching the top of the Pipe Line bed I found that the altitude of the entrance of the livin tunnels leading in to the Surge Chamber to be only 804ft. (aneroid) above the surface of the main anchor block at the Powerhouse instead of 900ft which is the amount of fall between the Surge Chamber
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and the Powerhouse, as given by the authorities. The barometer was falling, too, so that the aneroid reading should have been in excess of the 900ft. Either the generally accepted 900ft. fall is incorrect, or the aneroid was badly upset by the weather conditions, though tests I made on the spot seemed to be against the latter possibilirt. One test seemed to indicate that the barometer was falling at the rate of about one foot (on the aneroid scale) per minute. – this would give a height of only 764ft. for the Pipe Line (Main Anchor Block to Surge Chamber tunnel entrance). The second “pipe” tunnel leading in to the Surge Chamber from the top of the Pipe Line bed has now been driven but is not yet lined. Went in through the lined tunnel + found that the lowest part of the Surge Chamber is now bare concrete the boxing of the vertical-sided part having been removed. Above this the sloping sides of the pit have been lined for about half-way to the top + the pair on inspection shafts on the western side of the Surge Chamber are concreted to the same height. A narrow tier of boxing is raised in an ingenious manner as the work of lining proceeds
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In shape the Surge Chamber is not circular but polygonal, a shape which makes the construction of the wooden boxing for the lining very much simpler. All the concrete work is very strongly reinforced with heavy steel bars. Walked up to the top of the Surge Chamber + took 1/2pl. photos (6) + (7) looking into interior of Surge Chamber from east + west sides respectively. A strong wind was blowing which made photography in these exposed positions very difficult. Returned to Powerhouse + inspected same. The roof is now under construction + like the rest of the building is of reinforced concrete. The roof rests in part on trussed steel girders (each of which weighs 2 tons) 1/4pl. photo (8) of these – + in part on heavily reinforced concrete beams capping pillars of same construction; the steel girders are used where the span between pillars is large (as over the “generator” floor), + the other system where the pillars are closer together. The concrete roof is not quite flat there being a faint ridge running lengthwise to the building with a fall of one foot on either side. The
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drainage is into a shallow gutter on the inner side of a flat cornice about a yard in width. To render it perfectly waterproof the concrete roof will be finished off with layers of “certainted” roofing material + bitumen. 1/2pl. photo (9) of roof from NE corner showing construction. 1/4pl. (10) showing reinforcing of roof being put in position. 1/4pl. (11) of gang of men moving a “set” of reinforcing into position. 1/2pl. (12) general view of northern part of roof from hillside above Tokomaru Valley Road. Walked up to the 1st pole of Mangahao-Wgton City Transmission Line + took 1/2pl. (13) general view of Pipe Line showing progress of this part of the work. Walked up Pipe Line again + took 1/2pl. photo (14) of 1st “flat” + 2nd “steep” showing anchor blocks completed + the piers on which the pipes rest being fitted with their Muntz metal plates. 1/2pl. (15) of Powerhouse from zig-zag track alongside 1st “steep” of Pipe Line. Walked up Tokomaru Valley Road to Mangatangi ford, climbed hill on left bank + took 1/2pl. (16) of the narrowed spur at this spot. Left Powerhouse for home at 3.pm – passed Shannon 3.20. Home after battling with head wind at 4.30.