MORE POWER.

Taranaki Daily News, 18 July 1922, Page 6

MORE POWER.

NEW PLYMOUTH SCHEME. POSSIBILITIES OF EXTENSION. SOURCES OF MORE WATER. REPORT FROM ENGINEERS. An interesting report on the possibilities of hydro-electric extensions to the New Plymouth scheme was presented to the Borough Council last night. This question was recently prominently before the public, and last December Messrs. Sladden and Palmer were instructed by the council to make an extensive survey and investigation with a view to ascertaining what possibilities exist of increasing the water supply to the hydro-elec-tric extensions, with special attention to the areas drained by the Waiwakaiho. Mangorei. Henui and their tributaries. The report of the engineers is an exhaustive one, and deals with ail the possibilities of the district, recommends what are considered the most suitable schemes, and gives the approximate costs. The report states, inter alia: Our investigations show that the upper reaches of .streams which can lie diverted into the Waiwakaiho and Mangam ahoe watersheds are not suitable for storage purposes. The inclination of these valleys is such that dams up to 100 feet in height will impound only a comparatively small proportion to the results obtained. We have therefore largely confined our work to the lower reaches of the streams above the points in each from which the water can be conducted by gravitation to the Mangamahoe Basin at the necessary level. In connection with the above, certain approximate levels and measurements have been made around the area at the head of the Stony River, the outlet from which is near Bells Falls. Our conclusions with regard to this area are contained in that part of our report dealing with the Pouakai Basin. In addition we submit for the consideration of your council a scheme for the utilisation of the waters of the | Waiwakaiho and Mangorei a second time, [ that is, below the present power-house. In I each scheme only the total costs are given.

MANGAMAHOE VALLEY. As we previously reported, three dams could be constructed in this •. alley which would impound 18,890,000 cubic feet of water, at an estimated cost of £34,150. In making our calculations with regard to the utility and cost of storage, we have assumed a period of 30 days without fair: during which time the storage would be used. The above storage, after allowing for evaporation, would be equi v a’ent to 7 cusecs over the 30-day period With the head of water at the power station when this reserve would be drawn from, one cusec s equal to about 20 horse power on the -witchboard, therefore the above storage would give an additional 140 h.p. at a cost of £34,150, or £244 per h.p. With a load factor of 50 per cent., this would be equivalent to 280 h.p., .at a cost of £122 per h.p. In the above estimate no allowance has been made for the land that would be required, the area being about 27 acres.

WAIWAKAIHO. KAIAUI AND MANGAWARAWAR A. The Waiwakaiho Valley is of no value for storage purposes south of the Junction Road, the valley being confined as to width and of no great depth, and the inclination of the bed of the stream is too great to permit of any large quantity of watar being impounded. In the Kaiaui Valley we have contoured a portion of the ground which appeared to be the most suitable for a storage area, but the results are not very satisfactory. W’ith a dam about 40 feet in height, it would be possible to store some 7,000,000 cubic feet of water at a cost of about £12,000. This quantity of water would be equivalent to about 3 cusecs over a 30-day dry period, and would give about 60 h.p. on switchboard at a cost of £2OO per h.p. The cost of the land required is not included in the above estimate, the area being about 11 acres. The Mangawarawara, another tributary of the Waiwakaiho up the valley of which we have taken rough levels, is also of little value for storage purposes, the configuration of the country being somewhat similar to that of the Mangamahoe Valley, except that the Mangarewarewa Valley is more confined and therefore dams of the same height would impound less water. MANGORAKA. The Mangoraka Stream was measured towards the end of the dry weather which was experienced in February last, the flow at that time being 2J cusecs, which is equal to about 50 h.p. on switchboard. This stream could be diverted into the Waiwakaiho by a tunnel about 16 chains in length at a point on the Egmont Road about 1} mile south of the Junction Road. The cost of weir and tunnel necessary to carry out this work would be £l3OO, or £26 per h.p. on switchboard. The land required for this work would be under an acre, and is included in above cost, but the rights to tunnel below the property affected, and any reparian rights, have not been allowed for. MANGOREI AND HENUI. The Mangorei Stream was measured towards the end of February last, and was found to be carrying 13 cusecs. The valley is very deep, and over that portion which we have contoured we find that a dam about 90 feet in height would impound about 70,500,000 cubic feet of water. This quantity, after allowing for evaporating, together with the 13 cusecs flowing in the stream, would give 39 cusecs for 30 days. In connection with this scheme we have secured the rainfall Xlata over the last | eleven years, and taking the least annual I rainfall during that period, which corresponded in 1911, we find that the supply with the storage aforesaid would give 39 cusecs. The supply during this period Is governed by the first three months of the year, March being the driest month. The wastage during the remaining months of the year would be 300,000,000 cubic feet. Taking the mean monthly rainfall over the eleven years’ period, the results together with the 70,500,000 cubic feet of storage is equal to 44 cusecs. In our cal-

cularions we are taking the lesser quantity, viz., 30 cusecs, which would be equivalent to about 600 h.p. on switchboard. The tunnel from Mangorei would discharge into the Mangamahoe Stream about 35 chains south of the Junction Road crossing. We estimate that the cost of carrying out the work as outlined would be £45,000, or £75 per h.p. on switchboard. The Henui Stream, when measured towards the end of February last, was carrying 8 cusecs, which is equivalent to 160 h.p. on switchboard. This stream can be diverted into the Mangorei by a tunnel, but the valley is not suitable for storage and neither is the valley of the Pokeikatahuna Stream, a large tributary of the Henui, which junctions with the Henui a short distance above the proposed intake. The estimated cost of the work necessary to conduct this water to the Mangorei Stream is £5OOO, which is equal to about £3l per h.p. on switchboard. If the two schemes are combined the h.p. would be 760 at a cost of £66 per h.p. In the above estimates we have allowed for the land that would have to be acquired some 50 acres, but the right to tunnel under the several properties and any riparian rights that may be claimed have not been allowed for.

LOWER WAIWAKAIHO. The foregoing data has been obtained with the object of supplementing the supply at the present power station. We have now to report on a scheme that has always appeared to us as being worthy of the council’s consideration, and that is the utilisation of the water in the Waiwakaiho and Mangorei below the present power station. It has been stated that the minimum supply of the Waiwakaiho at the present intake is 150 cusecs. In our opinion this estimate of the minimum quantity is too high. From data that we have been able to obtain, we estimate that the minimum supply of the Waiwakaiho and Mangorei combined is only 130 cusecs, and in the following calculations this is the amount that we have based our results on.

Working out the quantity of water available from the least annual rainfall, ~whi eb occurred in 1911, in conjunction with the proposed storage at the works now being carried out, we estimate that 176 cusecs could be obtained, which amount would be increased to 214 cusecs if the Mangorei and Henui schemes were carried out. On the mean monthly rainfall during the same period the result, including the Mangorei and Henui, is 300 cusecs. Further large storage basins could be obtained in the lower reaches of the Mangorei Valley, but we have made no survey of these. The following figures are based on the 176 cusecs stated above, which, with the available head, 187 feet, is equal to about 2690 h.p. on switchboard.

We estimate that the cost of the work as outlined would be £85,000, including the cost of the land that would have to be acquired, some 40 acres, which we have valued at from £3O to £4OO per acre. Rights ! for driving first tunnel under the various properties, and any compensation that may ; have to be paid for riparian rights, have . not been allowed for. In addition to the above cost, the power-station and machiery would cost about £lB per h.p., or 48,420, making the total cost £133,420, which works out at about £5O per h.p. on •witchboard. In the event d£ the Mangorei and Henui scheme being carried out, the horse-power at this station would be ncreased to 3375, and the total cost, increased to £145,750, which works out about £43 per h.p. POUAKAI BASIN. Investigations have been made with a view to ascertaining what prospects exist of constructing a storage basin at the headwaters of the Stony River, to include the area usually shown on the maps as open swamp. This is an area of approximately 350 acres, or a little over half a square mile, from ’ which the northern branch of the Stony River issues through a narrow, rocky gorge abo\e Bells Falls. It will not be difficult to construct a dam above the falls. The swamp area has a total fall from the north-east to the outlet of about 200 feet, and a dam 200 feet high would t ! -refore be required to flood the whole area. With a dam about half this height we estimate that an area of 4$ million square feet can be flooded, with an estimated storage capacity of not less than 100 million cubic feet, if the water be taken out near the lowest point in the vicinity of the present outlet. It is, of course, desirable that the water should be taken out near this point, otherwise large quantities of water cannot be made use of. Suggestions have been made from time to time that this storage might be used to augment the present supply from the Waiwakaiho by turning it into the Kaiauai (a branch of the Waiwakaiho). This appears quite possible, but would necessitate the driving of a tunnel at least 90 chains in length approximately in addition to a ’dam. From indications it seems beyond doubt that such a tunnel would be extremely costly to construct, and in our opinion it is questionable whether the quantity of water thus obtained would Warrant the heavy cost. In view of this we have not gone into details of possible cost, and therefore submit no estimate.

Since the suggested storage is situated at an altitude of approximately 3000 feet above the sea level, advantage could no doubt be taken of the great head available to utilise the water at least once before it finally reached the Mangamahoe basin. In our opinion, however, the cheapest and best method of utilising the resources of the area in question will be to take advantage of the very rapid fall of the Stony River. A head of many hundred feet, possibly 1000, can be made available, and in conjunction with storage a useful supply of water can be assumed. It is extremely difficult to arrive at the minimum quantity of water that can be relied upon during the dry periods in this locality, and we have been guided in making our estimates by the Upper Mangorei records. The Upper Mangorei station is approximately 1000 feet above sea level, and three to four miles distant. The mean annual rainfall, based upon records for ten years, appears to be about 127 inches. Upon this basis and in conjunction with information gathered from persons who know the locality best and our own knowledge, we believe that the mean annual rainfall in the vicinity of Bells Falls may be taken at 150 inches. This indi.ates a probable average flow over the falls of about 28 cusecs. The lowest recorded rainfall for the three months of January, February and March in any one year, using the Mangorei data as a basis, appears to have been in 1911, when between 10 and 11 inches only fell, or equivalent to a probable flow of 8 cusecs due to rainfall. To this must be added the flow due to the numerous springs from the ranges and Mount Egmont, which are fairly constant all the year round. We therefore consider that we can safely take 13 cusecs as the average minimum flow for the three dry months, and 10 cusecs as a possible minimum in an exceptionally dry season, ’which may occur, say. once In _ U jrtoxMe, bs made avtulabie

as suggested, 100 million cubic feet would supply an additional 12 cusecs for a period of three months. From the foregoing wo conclude that with.storage a minimum of 20 to 25 cusecs will be available during the dry periods, even’ if lasting three months. This comparatively small quantity of water, used with a head of, say, 500 feet, will give approximately 1000 h.p. effective, or with 1000 feet head, a corresponding increase. This may well be found worthy of closer consideration in the future. OAKURA AND KIRI.

Wte find that it is quite possible to divert the Kiri Stream and to turn it into the Henui and thence into the Mangorei, to augment the present supply in the Mangamahoe storage. In our opinion the cost of this will be much too great in proportion to the extra quantity of water thus made available. The minimum flow of the Kiri is small, and is probably not more than 15 cusecs. The fall of the country is very rapid, and is such as to render any considerable storage out of the question. We therefore think that the most economical way of using any power available will be found by making use of the waters of the Kiri and Oakura together below their junction. The flow of the two streams together has been measured during a dry period, and is found to be approximately 35 cusecs. This agrees very well with the probable minimum flow as arrived at from rainfall records.

Levels have been taken. down stream from the junction, and the fall of the stream is found to average about 1 ft. per chain for the first 200 chains below junction, and the total fall from the junction to the sea is approximately 380 feet. We have not gone into details of any scheme to utilise the power from the stream, but it appears quite practicable to take the water out a little below the junction, probably on the southern side and by conducting it less than two miles to reach a point where over 200 feet of head can be made available. This would be equivalent to about 600 h.p.. with 35 cusecs the probable minimum flow. The water could be used a second time if necessary, with a head of 150 feet or more. As the fall of the river per chain decreases as it gets nearer the sea, it is possible that it may be found that useful storage can be obtained. We have not, however, gone into this, and merely offer the foregoing as an indication that the possibilities of the stream may in our opinion become worthy of closer investigation in years to come.