WATER FROM TAUPO.

New Zealand Herald, Volume LXII, Issue 18996, 18 April 1925, Page 11

WATER FROM TAUPO.

PROVINCIAL BOARD PLAN. REPORT OF THE ENGINEERS. COST NEARLY £2,500,000. TWO ALTERNATIVE SCHEMES. . CONFERENCE TO BE HELD The proposal to set up a provincial water board for the purpose of obtaining a water supply for the various districts around Auckland arid in parts of the Waikato district was further considered last .evening by the special committee appointed by the conference of local bodies held in Auckland last August. At that conference local bodies in the Auckland suburban area, the North Shore district, and along the main south line as far as Hamilton were represented, the Mayor of Mount Eden, Mr. E. IL Potter, presiding. It was decided to have a report made on the available sources of supply in the province, and Messrs. J. Rogers, engineer to the Mount Eden Borough Council, and W. Arthur Gray, chartered civil engineer, were appointed to carry out the investigation. The report of the engineers, recommending Lake Taupo as the source of supply, •was presented to tho meeting of the committee last evening, together .with a statement on the financial aspect. Mr. Potter presided, and the members of the committee present were: Messrs. L. E. Rhodes (Mount Albert), T. Lamont (Devonport), R. G. Clark (One Tree Hill), E. C. Walton (Birkenhead), G. E. Tansley (Mount Roskill), F. M. Waters (Manukau), J. E. Cowcll (Onehunga), C. F. Gardner (New Lynn), and P. H. Watts (Hamilton). After hearing the report and financial statement and having the scheme explained by means of maps and photographs, tho meeting adopted a recommendation that an Auckland Provincial Water Board bo formed for the provision of an efficient water supply and that a copy of the engineers' report be forwarded to all tho local bodies interested. It was decided that all the local bodies adopting the recommendation be asked to signify their assent to the scheme and that a conference be called when the replies aro received. Meeting Demands For All Time. In prefacing their report, the engineers stated that in view of the growing population in tho area proposed to bo included in the provincial district, they had deemed it advisable to propound a scheme adequate to meet tho demands of the popu-lation-for all time, and with a view to the installation of a permanent and inexhaustible supply they recommended Lake Taupo as tho source. They stated the lake had an elevation of 1211 feet above the sea, had an area of about 238 square miles, and was served by a catchment area of about 995 square miles. Tho lake discharged at its nortneast corner, whero its volume was estimated at 2860 cubic feet per secpnd, itnd this would ensure a never-failing * mrce of supply. The intake from the lake had been selected at a point near Kawakawa Bay, and 18 miles west from its outlet, where the water was crystal clear and its purity undoubted. In the event of the scheme being adopted, the engineers recommended that the Government be urged to proclaim a water-supply reserve over the drainage area along the western shore of the lake, to maintain the water at its present purity. This area is unpopulated and in a state of nature. The engineers submitted a plan showing the area proposed to be served as including the country between Taupo and Auckland, as well as tho Hauraki Plains and the district to the north and .icr -S'; the harbour. This would embrace 29 boroughs, town districts and road districts, with a combined area of 58,750 acres, but it was proposed to include about "50,060 acres in the board area. These figures did not include the city of Auckland. Fifteen Million Gallons Daily. They quoted figures compiled by the Government Statistician show'.-ig the r.opulation of the area from Cambridge to the city, and including the North Shore boroughs, as 201,495, and deducting the population of the city, the figure vould be 113,700. Basing the quinquennial increase at 10 per cent, as a safe estimate, they calculated the population to be served in 1950 at 331,000, or, inclusive of the city, 187,000. They took the figure of 200.000 as their basis. They selected 50 gallons per day as the consumption per head, giving a daily maximum on 187,000 of 9,350.000 gallons. They, however, propounded a scheme giving a maximum delivery of 15,000,000 gallons, this being put forward for favourable considertion on the grounds that on the gross magnitude of the scheme it was more economical to provide' for the larger supply as the benefit accruing would be more commensurate with the capital outlay. The maximum supply of 15,000,000 gallons would serve a population of 300,000 at 50 gallons per head until about 1950, when it might be necessary to provide an additional main. The question of thermal and seismic conditions was carefully considered by the investigators and they came to tho conclusion that there was no evidence of activity in the locality selected for the intake," so that the position of the intake and route of pipe line would be perfectly safe and free from seismic action. Tunnel Ten Miles Long. Tho selected route for the pipe line would necessitate the construction of a tunnel ten miles in length, commencing at tho foot of tho cliff on the lake shore and following a straight line through the range to the Mangakino Valley, terminating practically at the confluence of the Arataki Stream and the Mangakino River. From this point the line would follow the spurs and broken range to Maungatautari Mountain on the western side of the Waikato Ilivcr and close to tho Arapuni hydro-electric works. From this point the line would go north-west through tho Leamington town district at a point about 1 £ miles from the Cambridge boundary. It would follow the Waikato River through Hamilton to Frankton Junction, from where it would generally follow the railway line, except between Mercer and Papakura. The length would be approximately 155 miles. Tho intake, continued tho report, would be 6ft. below the level of the lake; a reservoir at a level of 1060 ft. would bo 1 constructed at Mau'ngatautari, estimated to contain two days' supply; a reservoir of similar capacity would be constructed at One Tree Hill at a level of 500 ft., and it was proposed to 'construct two break pressure reservoirs between the main reservoirs along tho line of route. Branch mains would be provided to supply towns : along tho route. Supply for North Shore. In connection with the supply for tho • North Shore boroughs the trunk line would pass through Point Chevalier and along the reef stretching partly across the harbour from tho Meola Creek and , through the narrow channel to Kauri Point. A service reservoir would be constructed at Birkenhead at 360 ft., the main I then following the Shortest route through i Northcote and across Shoal Bay to supply , Devonport and Takapuna. To fit in with . this scheme the pipes had been computed to vary in diameter from 36in. ,to 42in. " Although provision has not been made in this scheme," tho engineers say, " it i

is worthy of note to mention the fact that the height of the reservoir at One Tree Hill will govern tho supply of water to the whole of the service reservoirs constructed by the City of Auckland, and in the event of the City, Council deciding to join in the scheme for tho introduction of a pure water supply, the necessary installation could be completed at a moderate expenditure." Dealing with the cost of the scheme, the engineers estimated that the Taupo project would involve an approximate capital expenditure of £2,482,000, and tho period for construction would be largely governed by the time occupied in excavating 1 the tunnel. This amount would be made r . up of the cost of the intake and line to , Maungatautari, £612,000; Maungatautari , ; to Pukekura, £254,000; Pultekura to Taupiri, £372,000; Taupiri to Bombay, f £393,000; Bombay to One Tree Hill, | £331,000; local branch lines, £100,000; , valves, £25,000; land casement and legal . expenses, £5000; contingencies, supervision, etc., at 10 per cent., £225,000. Included in the total would be tho cost 1 of the reservoirs, which would be: I Maungatautari and Oue Tree Hill, £50,000 , each; Birkenhead, Taupiri, £20,000; Pukekura and Bombay, £IO,OOO ' each. Tho engineers then detailed two alter- 1 native proposals. The first consisted of a i plant to intercept the Mangakino River , at or near its confluence with the Arataki Stream, thus omitting the head works at the lako and the tunnel until financial 1 circumstances warranted their inclusion. The approximate cost of this scheme would be £2,239,100. Tho other scheme consisted of deleting for the present the whole of the works lying south of the Maungatautari 1 reservoir and substituting a pumping ] station and plant at Arapuni, lifting the water from the river above the dam site to tho Maungatautari reservoir, the surface level of tho water being 320 ft. This plant could subsequently be held as a stand-by or dismantled. Tho cost of this scheme, including all works irom Maungatautari to Auckland, would bo approximately £1,915,700, the working expenses being estimated at £SOOO per annum. Tho engineers made the point t,|in' tho Taupo supply would ensure an absolutely pure water without having recourse to filtration. Details of Financial Charges. In view of tho need for a comprehensive survey to portray thoroughly and accurately the great variety of works over tho entire route, occupying at ieast 18 months, the engineers recommended that authority be given for tho prosecution of such survey so that the works outlined might *be initiated at tho earliest possiblo date. A statement presented to the conference dealing with tho financial aspect of tho proposals showed that the charges on the main scheme would be: —Interest and sinking fund on £2,482,000 at 6 per cent., £148,920; offices and line patrol, £2000; total, £150,920, or, say, £151,000 Taking the lowest-priced alternative it was shown .that the supply from Arapuni would gravitate from the Maungatautari reservoir, and if delivery were made to a reservoir on One Tree Hill at a height of 300 ft. a portion of the water delivered would need to be pumped to a 500 ft. reservoir to supply tho higher areas. The cost of this scheme with delivery to a 500 ft. reservoir would be £1,915,700, and to a 300 ft. reservoir £1,620,000. The charges to be met, pumping to the 300 ft. level would be:—lnterest and sinking fund at 6 per cent., £.101,400; office expenses and Uno patrol, £1500; pumping at Arapuni, £5000; pumping at One Tree Hill, £1000; total, £103,900. Calculation of Revenue. Tho statement set out that the demaud from the country districts traversed by tho proposed main was certain to be substantial, but it was difficult to estimate tho amount and this had therefore been omitted. The population to be served must bo estimated 3J, years ahead, the time required for the scheme to be put in operation. At that time, assuming the city did not participate, it was estimated that there would be a population of at least 125,000 in the bortiuglis, town districts and road districts to bs served. Sewerage reticulation would raise the consumption to 6,250,000 gallons per day for that populationThe revenue from the sale of 6,250,000 gallons daily to the local bodies at Is per 1000 gallons amounted to £114,000, which was more than sufficient to meet the charges on the scheme by which water was first obtained from Arapuni. A consumption of 8£ million gallons per day at Is per 1000 would provide ,a revenue of £155,000 per annum, sufficient to cover the charges on tho main scheme and leave a margin. If the main scheme were embarked on immediately and consumption did not reach 8£ million gallons from the first, it would be necessary to increase tho unit | charge by a small amount, but this would 1 be wiped out and tho price lowered below [ Is as the consumption increased. Comparison of Returns. \ This point was developed in a table showing tho revenue to bo expected from \ varying consumption totals at decreasing charges per thousand gallons as under:— 1 Million Gallons Per Daily. Thousand. Revenue. 8£ .. Is £155.000 9 Is £164,250 10 .. 10id £159,700 11 . . lOd £167,250 12 .. 9d £164,250 13 . . fid £158,150 ; 14 . . 8d £170,300 1 The statement pointed out that it might be asked whether further increase in dej mand leading to eventual duplication • would not show a less rosy prospect and ' lead to an increase in price, even if only ' temporary. It was stated that this would not follow, as the engineers advised that : it would not be necessary to duplicate ! the whole line at one time. When the ■ consumption reached 14 million gallons f it would be timo to consider duplicating ! sections of the line. Additional expendi- ! turo of £500,000 would suffice for the ' first stage of the duplicating, to bo carried out to meet an increase above 15 million gallons. ! A Suggested Saving. ; Mr. Gray submitted a supplementary » report in which he suggested an alterna--3 tiyc of delivering water at Auckland,to a . reservoir at a height of 300 ft. instead of 2500 ft. above sea level. He estimated that ) this would make possible a reduction of £325,000 in the capital cost of the whole j scheme, while a reduction of £225,000 . could bo made in the cost of the scheme f as far as Arapuni. The saving would re- . suit from tho use of smaller pipes, 33in., s 36in., and 39in., giving the same delivery, t and from tho use of lighter section steel t for the smaller pressures. 3 The cost of pumping that part of the 3 supply required for the higher levels on i the other hand would not at first exceed f interest and sinking fund on one-tenth i of the larger amount, so that a substan--1 tial saving could be made. He also made reference to tho future duplication of. tho 1 main. He stated that when two mains i were working and more than half the doa mand could be met from a 300 ft. reservoir I there would be no advantage in carrying r both mains to the higher level, but if the 1 first main were carried to the low level I and the second main to the high level, i the pumping would later be eliminated i and an economy practised during the early l life of tho scheme. s Further, duplication of the main would best be carried out in sections, and while the second higher pressure pipe could be worked in series with the first lower o pressure pipe, the reverse would not hold ® good.