Overview
Sat. Apr. 30.
Up early + walked down to Stewart’s – lovely clear morning. Will + I left in car at 7.10 am – passed corner at Shannon at 7.40 + reached ford on Tokomaru Valley Rd. in Mangatangi Valley at 8.5 am. This ford is 13½ miles from Queen St. Left car at ford + proceeded up road + over hill via track up spur above the old timber tramline. A new line of overhead wires has been erected across this ridge. Reached tram saddle at 8.53 + Arapeti Camp at 9.5. More cottages have been erected here to replace tents, a big canteen is in course of erection + the eastern end of the No. [sic] tunnel is now being bored. We proceeded along service road – a new
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line of overhead wires (a naked cable of 7 copper wires 3୵16 inch thick) is being erected along here also, evidently to carry a power current though in which direction we could not determine. After turning corner beyond Hilltop Camp I took ¼ pl[ate] photo (1) of the service road looking south. The distance from corner to top of jig tramline is about 17 chains. Reached top of jig tramline at 10 am. Looking down into the valley we could see a very large building situated on the southern end of the fragment of high-level terrace, in course of erection, + this, we afterwards learned is to be the cookhouse for the workers on the Mangahao Dam when that huge work is started. Descended zig-zag track + walked up left bank past the power house which is now working, to the tunnel entrance where the tunnel contractors are now at work + have got in about 3 chains. ½ pl. photo (2) of tunnel entrance. The debris from the tunnel is run out in an iron truck + tipped into river. The track up river-bank now goes past the tunnel + supplies of sand + fine gravel are obtained from further up the river for concrete +c [etc]. We went into the tunnel which is
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in such hard country as to not require timbering. Three men were at work at the “face,” using power drills of smaller size but similar pattern + mounted on a beam jammed across the drive + driven by compressed air as in the Otira tunnel. So far greywacke + a band or so of the haematite-like red rock have been bored + at present the drilling is in very hard greywacke with the joints sealed with fine veins of quartz. The present progress is about 5 f[ee]t per day, the “face” measuring roughly 8 ft. x 8 ft. We next crossed the suspension bridge + visited the top of the high-level terrace where we found shaft sinking[?] for the purpose of testing the formation still in progress. An extensive camp has now been erected here, also a temporary cookhouse + engineers’ office. In course of conversation with a workman (who now holds similar views to myself as to the physiographic structure of No. 1 Gorge, with the difference that he believes the rock-wall between the old + new channels to be a great rock-mass which has slipped down from the steep face on the left bank of river), I learned that
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a pit about 25 yards from the edge of the high-level terrace is now down 64 ft. without finding solid rock, + that sinking is temporarily stopped, pending arrival of pumps, on account of large water seepage. We next visited a shaft located on the very edge of the steep face of the high-level terrace above the gorge – this shaft is being sunk to test the solidity (because of “slip” theory) of the rock-wall between the old + new channel of the river. The top of this shaft is 52 ft. above normal river level + its bottom is at present 5 ft. below that datum – the top of the shaft is 8 or 10 ft. below the top of the high-level terrace. I found that the “slip” theory re the origin of the “island” of rock is the one generally accepted by the men though the engineers incline to my theory which was it seems quite unthought of before I brought it forward. In spite of the probability of my theory, it is considered necessary to make sure of the stability of the “island” of rock by actual test before proceeding with the construction of the dam. At this juncture, a Mr. Cooper, who proved to be the contractor for this dam, joined us + overhearing
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our discussion asked if we knew who Adkin was as he had been unable to trace him in the Govt. service or on the University professorial staffs. I introduced myself + we had an interesting chat. After this Mr. Cooper took us up to the office + introduced me to Mr. Johnson, one of the resident engineers. This gentleman expressed his belief in my theory + said that my section of No. 2 Gorge had been upheld in every particular yet disclosed by the excavations. He also promised to send me a section showing the actual structure when fully disclosed so that I could compare it with my drawing. He asked me to let him have a copy of my paper and in answer to a question informed me that a trench across the high-level terrace to bedrock will be necessary. ½ pl. photo (3) of top of high-level terrace showing tents, cookhouse + shaft-sites. We were invited to the cookhouse + hot tea provided, this making a welcome addition to our lunch. Met Mr. Cherry, machinery installing expert + W. Bird. Left Mangahao at 12.30 pm. ½ pl. photo (4) of camp on high-level terrace from the
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zig-zag track. Returned via service road. ½ pl. photo (5) of a firewood shute [sic] leading down to road with carters at work. On reaching tramline which intersects road, turned down it to sawmill (2 pm) ½ pl. photo (6) of sawmill +c looking west. Very busy scene here, the mill being in full swing with big rimu logs coming in. Tents alongside mill + on ridge above latter, a row of cottages are under construction. The tramline leading up to the hill slopes under trig Z has now been abandoned + the logs are at present being obtained from the upper valley of the Tokomaru where we could hear a log hauler at work. ¼ pl. photos (7) of mill from flat below it + (8) same from ridge to the NW. Crossed small stream + ascended past terrace of cottages to ridge above Arapeti Stm [Stream] + followed its crest northwards till [sic] we could see into the valley of the Tokomaru. Descended a steep slope + reached Tokomaru R[iver] at western entrance of No [sic] Tunnel at 2.30 pm. Work at this end of the tunnel has just been commenced + we found Messrs Kyle + Gunton on the job, having got only a few yards into the
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rocky hillside so far. Took ¼ pl. photo (9) of miners + others at tunnel entrance. We visited the waterfalls (about 5 chns [chains] + 10 chns upstm [upstream] res. [respectively?]) + found their beauty partly spoiled by a slip + some bushfelling. Returned to tunnel entrance + took another ¼ pl. (10) more distant view of same. Followed tramline down Tokomaru to Arapeti junction. The only additional work that has been done to the site of the Tokomaru Dam is the sinking of more test pits on its western side at the foot of the long spur which runs out from the Te Paki Ridge + forms the lower boundary of the basin-like Arapeti Valley. The test pits which have been sunk to depths of 15 ft. or less disclose (as one ascends) first clay, rubble +c. + then a high-level deposit of water-worn boulders + gravel with much “pug” intermixed. The whole of the lower part of this long spur, as we noted later, seems to be composed of decomposed or detrital material so that here, as at Mangahao No 2 Gorge, conditions are less favourable for dam construction than was
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at first expected. Further downstream the Tokomaru gorge contracts to two precipitous rocky walls with steep slopes above, seemingly precluding at this point the existence of an old parallel channel, and the dam could perhaps be located here with advantage. If this were done the Arapeti Reservoir would be enlarged but the top of the dam in this new site would doubtless have to be carried to a higher level above the stream-bed than would be necessary at the present site. We walked back to the eastern end of No [sic] Tunnel which is now in a distance of 8 chns 10 ft. The tunnel entrance is approached by an open cut through heavy boulders embedded in clay (an old deposit of the Arapeti Stm) + this formation extends into the tunnel a short distance. A boy provided us with an acetylene miners’ lamp + we went in to the working face. Hand drills are still being used in this tunnel as power is not yet available, + we found two pairs of miners at work, in each case one man twisting the drill while his mate drove it into the rock with a heavy sledge-hammer.
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The formation so far met with in this tunnel is softer than at the eastern end of No. [sic] Tunnel necessitating timbering right to the working face. The formation appears to be a partially decayed greywacke, blue grey in colour probably on account of depth and distance from the oxydising [oxidising] effects of the atmosphere, but much affected by percolating water. While we stood watching the drilling several lumps fell from the roof and walls in the untimbered couple of yds [yards] at the working face and work in material in this condition is evidently rather dangerous. In this drive a ventilator has been installed to remove gasses + smoke after blasting; it consists of an iron pipe, 12 inches in diameter, leading out to the opener where it connects with a chimney of similar piping. A small fire is lit under the chimney just before the fuse of a charge is lighted + the smoke +c is drawn out in ¼ hr instead of one hour without the apparatus. We left Tokomaru Dam at 3.30 + walked back to car via Tokomaru Valley Rd – car at 4.40 – the distance from Mangatangi
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ford to Shannon rly. stn. proved to be 3¾ miles. Reached home at 5.35 pm. After tea drove to Levin for stores. On looking thro’ [through] today’s “Levin Chronicle” the finishing touch to a very gratifying day appeared – in a long article on the Mangahao Scheme, a very appreciative + flattering paragraph on my part in the determining of the unsuspected structure of the Mangahao No 1 Gorge, had been inserted by the Editor.