CITY'S WATER SUPPLY

Wanganui Chronicle, Volume 77, Issue 32, 7 February 1934, Page 6

CITY'S WATER SUPPLY

PROBLEMS OF THE DAY A VALUABLE PUMPING PLANT VISIT OF INSPECTION. Two small streams, one about three times as big in volume as the other, and both fed from a catchment area of roughly 1800 acres, for 31 years, have supplied Wanganui city with water. Both serve to fill the Okehu dam, one through its own natural course, and the other along an artifi-cially-constructed pipe line that, at one point, finds a way through a shellrock tunnel that ia lined with glowworms. Yesterday, members of the Wanganui City Council, accompanied by the city engineer (Mr L. F. Row) and his assistant (Mr V. C. Rapson) paid a visit of inspection to tho site where these two small streams converge and create the Okehu dam. Most city folk, conscious always of effective water pressure in the city mains, have an imaginary picture of the Okehu dam as a place of big dimensions. A vast volume of water is visioned that has about it some pretension in its claim to be able to meet the requirements of a multitude of 25,U00. But there is a wide difference between the actual and the visionary pictures. The dam is an ordinary volume of dammed water, and the two streams that feed it, at this time of the year at anv rate, are little more than eighteen inches across. The setting is picturesque, perhaps. Bush, cool and refreshing, against a background of fern-covered, stockless property that extends to higher levels and invites rainfall. All through that area, little springs from the shellrock feed the Okehu parent stream and the Managahoropito. They, in turn, find their way to the concretewalled dam, and then to an outlet that sends them rushing down on their falling journey through the mains to the city and the sea. Yesterday’s visit was not one of idle curiosity. In a very short time momentous decisions will have to be made with regard to Wanganui’s water supply. Thirty-one years ago, when the Okehu scheme was constructed, a single main did duty from the dam to the city. As the population grew and the demand for water increased, the Okehu supply became less able to fulfill its obligations, and to add to the worries of those entrusted with civic’ management, certain tunnels, through through which the pipe line passed on its way between the dam and a point opposite the “Bushy Park’’ homestead, caved in. Some little time ago, if a break had occurred in those deeplyburied portions of tho line, the city would have had to strnd by without water until the repair job was carried out. That task might involve a period of anything up to throe months. It was a problem such as this which i presented itself to the late city engineer (Mr. J. S. L. Deem). He had an uneasy knowledge that at any time a break was likely to occur, and, to add to his anxiety, seepage from the Okehu dam started to .ob the volume of water. It is to his credit and to that of the council that supported him that he found a way to meet the difficulty by installing an auxiliary pumping plant in the Kai Iwi stream. Fortune favoured him when the work was put in hand, in that two springs were found of pure water, and there was no need of a chlorinating plant in the meantime, as the waters of the stream proper were not required. Such is the position to-day that if a break did occur in the tunnelled portion of the Okehu line the Kai Jwi pumping plant would be able to keep Wanganui supplied with water, on a very restricted basis, until the break was repaired. That is quite satisfactory so far as it goes, but a danger lies in the fact that all the pipes that arc deeply buried by the cavcd-in tunnels are approaching the end of their normal life, and the problem arises of a new line altogether. That would involve very heavy expenditure and loan money would be required. The Kai Iwi stream, fortunately perhaps, presents an alternative. Installation of another pumping unit, at a cost of round about £l5OO to £2OOO, would moan that the city could, if necessary, proceed independently of the Okehu supply. That task could be accomplished out of revenue and the cost of power for pumping purposes would have to be weighed against the cost of any capital outlay involved in renewing the pipe line to the Okehu dam. What the City Fathers will be called upon to decide in the near future will be whether it is worth while expending a large sum of money on a now line to Okehu. or whether nn extra pumping unit should be installed at Kai Iwi and further calls made on a stronger stream. Superficial reasoning certainly suggests the latter course, and on closer examination it will probably be found that it is tho best one to adopt. At present the city i.s fed from the Okehu dam, supplemented by the spring water that is pumped from Kai Iwi. There is a 16-inch single main from the dam to the break-pressure tank, near the “Bushy Park” homestead gate. From there to the Westmere reservoir there are two mains, one a 14-inch and the other a 12-inch. From Westmere to Wanganui there is a single 15-inch main. Duplication of the length between Westmere and the city will be another task that will have to be faced. These matters interested yesterday’s inspecting party, and at present it would appear that a further pumping unit at Kai Twi meets with favour. Mr. A. E. Halligan stated definitely that the plant should be put in as an insurance against what is liable to happen at any moment nearer the Okehu dam.