£35,000 SCHEME

Gisborne Herald, Volume LXVIII, Issue 20632, 13 August 1941, Page 4

£35,000 SCHEME

ABUNDANT WATER DAM AT MANGAPOIKE ENOUGH FOR BIG CITY ASSURED FOR CENTURIES A scheme to provide ample water for Gisborne up to a population or 20,000 at an estimated cost of £35,000 is recommended by Mr. F. W. Furkert. formerly Engineer-in-Chief of the Public Works Department, in a report which was considered by the Gisborne Borough Council last night. With extensions to the scheme, a population of 100,000 could be catered [or and a supply of water assured for centuries, Mr. Furkert stated. “Although I have worked out the cost of water on the assumption that the ' works, including land purchase, will cost £40,000, I do not think more than £35,000 will be required,” Mr. Furkert stated. "It would, I think, be as well to approach the Loans Board for the larger amount so as to have a reser\ e in case the very unexpected was encountered, either in Nature or in world market and labour conditions.” The report did not favour the dam site surveyed near the present Te Aral intake. Natural erosion in the valley threatened a short life and enormous floods made the problem of dealing with the overflow a matter of concern, though if there were no other alternatives the adverse circumstances could be overcome—at a price. The cost of a 60ft. dam was estimated in 1937 at £40.000, but it would cost considerably more to-day, probably between £50.000 and £60.000, and before any infilling took place would hold only 60,000.000 gallons, the cost of which would approach £1 per 1000 gallons stored. Over the hill in the headwaters of th& Mangapoike there were the Puninga ponds, really wet swamps. Three of these had been surveyed and were shown to be excellent storage basins when dammed at moderate heights. One which was most favourably situated would store 200,000,000 gallons at a cost which should be well 1 within £15.000. and it should not be subject to in-filling of denuded material. The cost of storing water in Mangapoike would be only Is 6d per 1000 gallons. Tunnel Under Hill Mr. Furkert discussed four possible methods of taking the water from the dam at the Mangapoike side to the intake at Te Aral, including the present method of pumping, undertaken during dry spells from Mangapoike Creek, and he recommended taking the stored water in concrete pipes for a quarter of a mile to the portal of a 95 chain tunnel under the hill into one of the tributaries of Te Arai Stream, by which it could find its way into the present intake. The tunnej would cost about £IO,OOO and the short length of pipeline about £2OOO, the pipes to be buried on an alignment not liable to slips. An allowance of £3OOO should be made for lining the tunnel where required, but lining might be unnecessary except for a short distance at each portal. The size of the tunnel would be dictated not by the quantity of the water passed, but by a consideration of the easiest size for driving. He did not recommend building a dam at the first of the Puninga ponds that would be lower than that required to store 200,000.000 gallons, for quite apart from the extra cost per 1000 gallons stored with a modified scheme there was the objection that the comparative shallowness of the water would allow it to warm up in the summer to encourage the growth of weeds, algae and other objectionable organisms. The area of the land which drained into the first pond was about 400 acres, but the rainfall was very heavy, being in part of the locality lOOin. per annum and ranging down to 85in.. If the lower figure was taken as the average and even if in a dry year the fall was only 60 per cent of the average, there would be sail 57in. which, falling on 350 acres, would produce more than twice the water necessary to fill the reservoir so that ample allowance for evaporation and soakage was available. Second Dam Site “There is a splendid site for a second dam in an adjoining creek within a quarter of a mile of the one referred to above, where for £25,000, additional water could be stored adequate to provide for a population of 30,000, while if the per capita consumption were reduced to Auckland’s 62 gallons per head there would be ample for 45,000 people. If conditions, such as we cannot now visualise, brought the population to be served ■up to 100,000 a moderate heightening of the dams would cope with the position. The proposed tunnel would still be adequate. “In view of the above. I consider that the combined watershed amounting to approximately 1000 acres should now be acquired and gradually afforested with valuable trees and native underscrub. If this is done Gisborne’s water supply will be assured for centuries; even if oil is struck.”

Every effort should he made to carry on with the present pipeline until 1957, when the borough's financial position would be greatly improved with the liquidation of a considerable portion of indebtedness, but Mr. Furkert was doubtful if it was possible to carry the pipeline on till then. If an 18in. pipeline was laid on a safe alignment, there would be ample capacity for 50 years. “When I say 50 years,” the report went on, “I have in mind the use of concrete pipes for the portion within which these pipes can be used and steel pipes lined with concrete for the balance.” Probable Fixed Charges Assuming the replacement of the pipeline was necessary before 1957, costs would be as follows: —Present fixed charges £7142, equalling 4.7 d per 1000 gallons on 305,000,000 gallons; fixed charges on Mangapoike works, £2OOO (£40.000 at 5 per cent); fixed charges on new pipeline, £4675 (£85,000 at 51 per cent, estimated cost of 18in. main); total £13,817, equalling 8.3 d per 1000 gallons on an annual consumption of 400,000,000 gallons or 6.7 d on 500,000,000 gallons. After 1957, when fixed charges on the old pipeline were liquidated the position would be: —Fixed charges on Mangapoike works, £2000; fixed charges on new pipeline, £4675; maintenance, £550; total £7225, equalling 4.35 d per 1000 gallons on an annual consumption of 400,000,000 gallons or 3.5 d on 500,000,000 gallons. (Further reports on the water scheme appear on Page 7.)