COBB SCHEME

Nelson Evening Mail, Volume LXXII, 30 November 1938, Page 13

COBB SCHEME

MINISTER IMPRESSED Thus the visit of the Hon. R. Semple to the works yesterday had no ordinary significance. He was accompanied by

’ Mr J. Wood (Engineer-in-Chief of the j Public Works Department) and Mr T. | i A. Johnston (District Engineer), by j i | the Hon. G. R. Hunter and Mr H. H. | t Sterling (Directors of the Hume (Cobb t River) Hydro Electric Company, Mr L. R. Pearless, resident engineer on the r works for Vickerman and Lancaster, r ; consulting engineers to the Hume (Cobb t - River) Electric Power Co., and Mr A. [• F Downer, of Downer and Co., Ltd.. 1 contractors l'or the access road, power t f house, and dam. i The tramway which has been 1 constructed in three stages up the side ( of the mountain 3000 feet high, is, in;' itself, a large undertaking, and the Min-T ister was quick to grasp the extent of I j hard human labour involved first ml cutting the line up the steep bush-cov-1 ered hillside and then in grading the! track and in taking up the rails. There j ( are three large winches operating sections of the tramway and it was inter-! esting to watch the strong wire cables . thickly coated with oil wind and un-i wind on the drums as the trucks are! hauled up or let down the tramways. It was raining heavily when the Minister and party were on the line * yesterday arid heavy tarpaulins were requisitioned to give partial protection from the soaking rain. At the end of the second stage—it is H in some respects almost likd a railway station—is the main camp of those who j have been engaged on the track. It is near this station that the tunnel is •_ being driven through the hill to the I e Cobb Valley and the air compressors)

lare at work supplying power for the ( y drills. The tunnel is being made by aI t co-operative party. jc 1 OVER THE MOUNTAIN jl ] This “station” near the mouth of the ( j tunnel is on practically the same leve Mi as the floor of the Cobb Valley on the j other side of the mountain. But access | must be gained to the Cobb Valley to j j j build the dam simultaneously with the ; J tunnel work which is proceeding from I . both ends and for this the mountain ; | must be crossed. There is a further j line to the top and then a motor jour- • i ney on a practically level road along the ridge for some three miles to a point overlooking the valley of the Cobb ■ and the site of the dam. The party yes--1 terday had the ride of their lives stand- ; ing up on the floor of the lorry as far ; as canvas cover which afforded some l protection from the downpour would ; permit. The difficulty, however, was to maintain a footing while the lorry 5 squelched and bumped over the unform--1 ed road. However, it was carefully : driven without the sudden starts and stops that would have scattered the 3 human freight in all directions. From the road at this point a jig line of about 800 feet has been built in order to convey material for the dam construction work down to the valley of ! the Cobb. Some thousands of tons j will be hauled up the long lines, j e loaded into motor truck, taken to the t y | ridge overlooking the Cobb and lowerV Jed down to the Valley floor. It is a big j

job in every respect, but modern mach- I inery is being used throughout and the rough nature of the country appears to present few, if any difficulties now that the initial work has been completed. Very acceptable morning and afternoon teas were provided by Mrs Skilton at the second stage of the journey up the tramline. The Minister's first view of the Cobb Valley was a very restricted one owing to the fog and rain. However, almost in a few seconds it cleared and the long open valley which is to be the bed of the lake to be formed came into j view. Immediately below the huts of | those engaged were seen. SITE OF THE DAM 1 The photograph gives a good indi-< j cation of the Cobb Valley where the! j river is to be dammed. It is all most j interesting and unique and of j i the greatest value from the point ! [of view of the generation of hydro-1 electric power for here is this wide, j open valley floor 1860 feet above the river level on the other side of the mountain, for alter leaving the Cobb Valley the river falls rapidly to a level as stated above. 1860 feet below. Water lor the turbines, however, will be taken through the mountains by means of a direct fall to the power house. THE COBB VALLEY DESCRIBED I One of the most interesting features j of the Cobb Valley, easily discernible

iyesterday when the mist cleared. is 'that while it is in mountainous ! country, it is not narrow and spurlocked as are the bush-covered valleys seen in the course of the long ride in the jig tram on the other side of the mountain. Mr T. J. McKee, B.Sc., of Tasman, in the course of an informative article on the Cobb Valley in “The Mail” gave the appended ini teresting description:— “Above the gorge (near where the dam is to be built) the river is well ; graded, as there is only about 50 feet fall in the first four miles. The floor of the valley is free from forest for the first six miles above the gorge, after which occasional tongues of birch forest extend across the valley floor, but there are still considerable natural clearings. Above the junction of the Chaffey stream the valley is very boggy for some miles. There are also extensive ( boggy areas between Mytton’s Hut (which is immediately below Mt. Peel) and the gorge. For the most part the , steep valley walls are clad in dense birch forest. i V-SHAPED AND TROUGH-LIKE “Normal river valleys are usually . more oj' less V-shaped in profile, with I interlocking spurs; whereas glaciated ; j vallevs are usually trough-like of U- , I shaped steep valley walls and broad : | valley-floor and very often the valley -! spurs are completely truncated. ValJI leys which have been glaciated usually

become over deepened at the head so that., when the ice retreats a lake is formeev. Lake Cobb was probably formed in this manner. The Cobb Valley is somewhat U-shaped and troughUke Moraine and large-sized “erratics” (rocks which have been transported by a glacier) may be seen in the Cobb Valley. Also many ice-smothered domes of rock troches mouotnees) on which occasionally one finds long (lutings which have been formed by the gouging action of icc. On the Burgoo Saddle, not far from Lake Cobb, may be seen many acres of hummocky (mamillated) ice-smothered rock surfaces, and on the lower peak of Mt Cobb there are numerous rock terraces which are typical of ice-stream erosion. I There are indications that the ancient | Cobb glacier ougtrew the valley and ' debouched over the lower northern | slopes of the Mt. Arthur Tableland, by l way of a low and broad saddle about | 800 feet above the valley floor. Not far | from the track to the Asbestos Claim [morainic deposit may be seen. THE ROCKS OF THE COBB VALLEY “The Cobb River is entrenched in a very old geological formation, in which many different rock types arc encountered. Where the river enters the gorge a very hard intrusive igneous rock, of a type known as ultrabasic, is found. The outcrop of ultrabasic continues up-val--1 ley for about a mile, where its place is 1 taken by very old sedimentary forma-

tion which consists mostly of Haupiri conglomerate, and which is found to continue for about another seven miles. This conglomerate is very hard and | weather resisting, and is of interest as | at some remote period in time it has been subjected to pressure so great | that the constituent pebbles have been j flattened and distorted. “Next come the rocks of the Mt. j Arthur series, which are made up of ' hard quartzites and softer slates and | phyllites. These last two types of rock I are really fine grained sedimentary rocks which have been metamorphosed (or altered) as a result , of being for a great time—perhaps millions of years ago—under the pressure of younger overlying sediments. “Most of the rocks of the Cobb Valley are recognised as belonging to the Ordivician system, which were deposited eons ago when the most advanced form of life consisted of primitive fishes. “It is interesting to note the oldest rocks known in New Zealand—the Ordivican—occur only in the South Island, in north-western Nelson and Fiordland. “About two miles from the head of the valley an older series appear which are known as the Lower Aorere series and are of Lower Ordivican age. The formation consists mostly of schists which have been greatly contorted by intense folding. . . THE TUNNEL Extensive progress has been made with the construction of the tunnel, which will be one mile 40 chains in length. The rock looks hard and firm. The wet weather outside made no appreciable difference to the tunnellcrs inside. Mr Semple was also impressed with the access road from Upper Takaka to the power ■'tation. CONSTRUCTION OE ROAD Sheer rock faces, huge boulders and heavy bush were encountered in the construction, but a bulldozer worked wonders on the rock-strewn hillside last year One minute it appeared to be pushing' at a large mass of rock which was unresponsive. Next minute debris which had been loosened was being pushed down the almost precipitous slopes. A miscalculation would, it seemed, send the machine and driver downhill to the rocky riverbed below. To the visitor it was difficult to determine which was the more dangerous - the risks of falls of loose rock which had been disturbed, or the risk of shooting over the bank as the material was ; being pushed over—a real pioneering job as the Minister would say. A picture shows the kind of work undertaken on the sheer rock faces. PIONEER ENGINEERING WORK The engineering work involved in determining the approach to file Cobb ' Valley must have been fraught with ’ the greatest difficulty and responsibili ity. considering the nature of the coun--1 try. as rough and precipitous as anyi where in New Zealand, said the Minister . yesterday. This work was carried out foi > Messrs Vickerman and Lancaster bv

Mr Roy Lancaster who is now Assistant 11 Engineer to Mr T. A. Johnston. District ! C Engineer t:

he dam. but he 1 ad a good view of the N)bb Valley from the top of the mounain when the rain and mist cleared nomentarilv. Mr Semple said lie intended to come again in the summer and take a moving picture of the whole system to show the people of New Zealand what engineering difficulties, what huge undertakings, and what work were involved :n the generation of