POWER BY WATER

New Zealand Times, Volume XLIII, Issue 10138, 28 November 1918, Page 8

POWER BY WATER

SCHEME FOR NORTH ISLAND

HOW ECONOMY AND EFFICIENCY WILL BE EFFECTED.,

A comprehensive report by Mr E. Parry, M.I.E.E. (Government Electrical Engineer), setting out proposals for the electrification of the North Island by means of hydro-electric power, was placed on the table-in the House of Representatives yesterday by the Minister-'for Public Works (Sir William Eraser). The scheme comprises the development of the three principal power sources, namely, Mangahao, Waikaremoana, and Arapun> (Auckland). Mr Parry states that of the three sources Mangahao, with which it is proposed to supply Wellington, is the best situated in respect to the load and it is to be regretted that this source is not capable of yielding a larger amount of power. Tlie general scheme falls shore of the ideal in two other respects, namely, the lack of a moderate!}’ large source of power in the Taranasi district and in the Whangarei district. However, the scheme advocated was the pest under the circumstances and while being adequate, economical and eminently pi™’' ticable at the stage described, it can still bo further developed and enlarged ns re quired. It is recommended that in tlx 1 interests of national economy and pic* duction the scheme should he planned in such a manner and on such a scale toal a supply of power shall be available with the co-operation of the local author ities for every householder in the Aiith Island, or for' any industry requiring supply of power, temporarily or <Auwwise, for main line electrification liffbrailways, coal and other.mines, for wuming, pumping, ventilating, and smelting and for any'other purpose. The power to ha provided is equivalent to one-fiith of a horse-power per head of ♦he piesent population of the North Island, which provision is ample for ordinary requirements, hut not sufficient for such extraordinary developments ah have taken dace in Tasmania. . The total capital expenditure is estimated at .£7,559.411, including m‘» res J; during construction, working capital ana a sum to enable financial assistance to be afforded to power users and local authorities. It is pointed out that the whole expenditure is recoverable in from six to seven years in coal only, productive power is increased and economy secured . country district ; settled, and closer settlement accelerated, whilst at the same time the undertaking is wlfbupportinsr after a reasonable interval ioj development and growth. On the basis of 71 per cent, per annum the capital charges will amount to -£>47,/28, and working expenses are estimated at 000 per annum, making a total of 728, requiring an average return of A 5 9s per h.p. of substation toad, which should be easilv secured. Mr Parry deals with the various aspects of the question under the following heads-—Function of hydro-electric power in the State, electricity Jn agriculture. electricity and industry in general, electro-chemical and electro-metal-lurgical industries, electrification of main line railways, electrification of suburban railways, agricultural railways; electricity in coal mines, electricity in mining generally, general principles affecting the generation and distribution of power, and the development of the general and subsidiary schemes. THE MANGAHAO SCHEME 1 .

Dealing with the proposed scheme for the Wellington district Mr Parry states that Mangahao River was selected as the best available source of supply. The power is obtained by diverting the waters of the Mangahao by a tunnel one mile long from a dam on the river through the hills first into a large regulating and storage reservoir formed by damming the Tokomaru Creek, rear the old sawmill, and then from this reservoir through a second tnnhel 1 mile 36 chains long out on to the hills at the back of Shannon. From the end of this second tunnel steel pipes 56 chains long will carry the water to the powerhouse at the junction of the Mangaore and Mangatangi creeks, about 3 miles from Shannon, and give a fall of about 900 feet. The flow in tho Mangahao River is very variable, and provision has had to be made for storing water to carry over tho periods of low flow, which occur periodically. The main storage will be in a dam at the tunnel intake on the .Mangahao, which will be directly connected with the other main dam on the Tokomaru. Further up the Mangahao will bo a second dam not directly connected to the tunnel, but which will also store a large quantity of water, and which will in addition stop any shingle which is being carried down the river. When working on such a high head, storage capacity is of very great value, ai d the extent to which this value Is to he depreciated by moving shingle filling up the reservoirs has been very carefully considered.

SOME ADVANTAGES DESCRIBED. The greater portion of the drainage area of the Mangahao above the proposed intake is in standing bush, mainly forest reserve, which protects the slopes from detrition, and although the river is subject to great fluctuations in flow our observations show th.at it carries a comparatively small amount of debris. The difference between the stream and some of the other Wairarapa rivers, particularly the Mangatainokn, which flows in the nest valley to the eastward, is very marked. It will be noticed at once that whore these two river? emerge from the hills on the Wairarapa side, the Mangahao runs in a deep vaMcy, only changing its course occasionally as it erodes away one or other of tho banks, while the Mangntainoka runs on a level almost with the surrounding country, and is constantly changing its course in floods. The difference between tho two rivers is due in the main to the fact that Mangatainoka brings down from the hills more shingle than it can transport across the flatter grade, into the Munawatu, while the Mangahao brings down scarcely enough to keep pace with the erosion from its lower reaches, end so has no tendenev to build up its bed. ~t is to be expected, however, that there will be some filling up of the upper reservoir but this will keep the main basin lower down on the Mangahao clear for a considerable number of years, whilst the, reservoir' in the Tokomarn, not being in the main river, will be clear at all times. By the lime any filling up of reservoirs will have'materially depreciated the storage value, the Mangahao scheme will have become linked up with the large schemes to the north, so that a small reduction in output on that account will not be of serious moment. It is also quite nossible to build smaller dams as required higher up the river to prevent shingle reaching even the upper dam ns now designed. IN'DRY SUMMERS.

Very careful observations of the river during the drv summers in 1916 and 1917 suggest 24.090 h-P. ns being the maximum plant capacity to install on this scheme and during very dry summers ono-'of the units. 6000 h.P.. tronld need tn he a spare. The complete installation fo- delivery on to the main transmission I'"eis estimated to cost -G£VS,C.j4. This amount, which is equivalent to .£lB 3 per h.p. of plant capacity, though not qu’to so cheap as fe»- =orne of the larger developments at Waiknremnana and on tho Waikato in generating cost, is quite a reasonable figure for a. development of this size, and when in particular we 1 consider that it is almost at the centre

of gravity of a load which, will in a very short time absorb the whole of the power available the development becomes a particularly good one. SOME COMPARISONS.

Compared with Coleridge the capital cost per h.p. to deliver to the transmission line if the complete development is put in is less than at Coleridge at its present stage, though not quite so cheap as it will be in its ultimate stages. Xhe running oost per h.p. on account of the larger development will also be cheaper at Mangahao, while the average distance over which the power has to be transmitted is also less, and though the cost of transmission, per mile will . 6 9? ie r what greater, there is no doubt but that at rates comparable with Coleridge the scheme would be paying" all charges in a very short time.

THE GENERAL UNDERTAKING. With regard to the three main generating stations, Mangahao. Lake, W aikaremoana, and Arapuni. Gorge, it, will be noted that the Mangahao power station is almost ideally situated for the supply of Wellington district, as it is within a few miles of the centre of gravity of the load. So also Waikaremoana, is very favourably situated for'the * supply of the East Coast district.'Arapuni/or alternately Aratiatia," is-father far-south for the most efficient supply of the Auckland districts, but when wo consider that Mangahao is unfortunately, rather small for vhe ultimate requirements ot Wellington and Taranaki, which ''Will later bare to augment their supply from sources further north, these Waikato stations are particularly well situated. , , To make the arrangement of generating plant ideal we would need toh&ve a source of 50,000-h.p. in place of the present limit of 24,000 at Mangahao, a cheap source of about 20,000 h-P- capacity in the Taranaki district, and 10,000 h.p. in the Whangarei district. A search for a suitable and economical source in the Taranaki district of the desired size has proved, fruitless. Smaller developments are possible and at comparatively great expense for the limited amount of power obtainable, and it is found that the Taranaki district can be more economically and better served by transmission from Arapuni and Mangahao. ■ ,

The (main high tension lines from these main sources of power will be-seen to follow the most practicable route to serve the load centres, while at the same time they have been laid out with due consideration to the locations in which development is most likely to extend. From the substations other lines at lower pressure will,, radiate'opt to' other substations, ensuring a supply to the whole of the island. It is proposed that the department should sell power wholesale to local bodies who will erect all-'Sistribution lines and operate the retail business within an area of supply surrounding each of the main Government substations. ESTIMATE OF THE COST. The complete estimate. for the general scheme of electricity supply is given by Mr Parry as follows;—^ Generating stations (total plant capacity : 160,000 h.p.): Mon* , gaiao, 24.000 h.p., cost X 438.654: Waikaremoaha, .40,000 h.p.. cost .£544,368; —Arapuhi, 1 85,000 h.p-, cost 1 ' iE1.078.700.-' > * Total cost . ....... 2,061,723 Main transmission lines ......... 1,653,880 Extra branch transmission lines at lower voltage to main sub- . stations not on main line’...s. . 7 241,360 Main substations 838,808 Distribution, lines and second- . arv substations :.. 2,086,000 Interest during construction ... 271,271 Assistance to local authorities and power users 100,000 Working capital (a ' 160,000 Total cost 7,303,042 Total cost per horse-power ... 46-63