DUPLICATING MAINS.

Dominion, Volume 3, Issue 797, 21 April 1910, Page 2

DUPLICATING MAINS.

FROM WAINUI. THE ESTIMATED COST: £79,688. ENGINEER'S' BBPOET ; A scheme for the'duplication .'of the water maiu from the reservoir atWainui-o-mata has been prepared by the city engineer (Mr. Morton) for. consideration by - the City Council. .' t • Mr. Morton states that the . present main consists';of a line of-30in. ca6t-iroa • pipes from the reservoir to the city side■ '■ of the Waiwetu Hills, 24in. pipe from the hills to the old city boundary,, and smaller pipes in the city. Tho 30in. main, is capable of discharging sufficient water • to supply a population of' about ■ 150,00> \ people (allowing 50 gallons per head.per■;';•_. day) and the pipes are thick'enough to • withstand the' pressure to which they are subjected. This portion of the main has ' given little or no trouble, and with the / exception of three pipes in the tunnels: which have been known ;to be damaged for some years, and excepting also those portions laid under . the stream, the ' whole of this main appears to bo in good order and condition.; This portion of the : : main should not require to be duplicated for ' some considerable, time, to',come. The 2«n. main, however, of which tho pipes aro considerably less in thickness than is usually considered advisable for . the pressure to which they are subjected, has given a considerable amount of • trouble. If it were not for the assistance ■ given, by the reservoir to the city supply, this main would now. be . quite incapable of meeting the demand* made during'daylight hours. The extension of the sewerage system :'; i will necessitate the provision' of" mbro"' water for flushing purposes. : The cor-' i ! poratidn has agreed to supply water ta tho borough of Miramar, and it is ex- ■' pected that before long' a similar agree- - ment will be sought by the 'Karori Borough Council. ■; . ■"-,-;■''. '"•',- Was it Recommended? Hence Mr. Morton recommends :--(l). Duplication (with 21in. pipes) qf the main between the Waiwetu Hills and the city, to be taken in hand at the earliest,possible opportunity. -, '■--.'.'. '.;-''. (2) In connection with the duplication,! ; provision should be made for the con- ■'. struction of •a ■ distributing reservoir •' capable' of holding, say,' 2,000,"000 Igal-.' lone, on a suitable site close to the city. ' (3) The existing 30in. main should be . , carried over the Wainui ; Stream op. bridges; instead of through, tho stream as' at present.'" .'■ '" ' : The duplication _6hould .consist :of *',( 21in. diameter main connected ;with *'-'■', suitable junction at the outlet of the tunnel'on the .Petone side of the "vV^ai-; wetu Hills. The new main'should ' be' ■• ' carried through Petone, alodng the. Hut't ;," Road, Thorndon Quay, Lambton Quay, Bowen Street, Wellington Terrace, Ghuz-;■•.. nee Street, 'Willis. Street, andV.Nairn""; ' Street to "a distributing' reservoir., above the : Nairn ; Street reserve,, at a'level "of-v. about .300 feet above the'-seal Under the i new system the mains supplying tho city from Wainui : -"and ' the distributing reservoir would be capable of delivering "'! 6,950,000'• gallons' daily, and, "in addition, • the distributing reservoir . would, be. ' holding 2,000,000 gallons'.' incase of : injury to either the' new 6 rexisting main. The daily discharge of this 21ini'main is estimated at'.■".' about 2,700,000 gallons, with a pressure at •'• , the. centre of the city equal to 300 ; feat , head (1291b5.)...:;,"',, . ./:. ; Distributing Reservoir. , .The advantages to.be derived in supplying through a distributing reservoir-are - set forth as follow The rate,of.discharge in the trunk main and the presr , sure maintained throughout - the • whole . system are more uniform throughout ; rwenty-.fohr hours, therefore, there is less ■ shock in. tho mains than when- the- con- • ncctioic is : direct 'to' the'/reticulation sys-; :'■■■• teni. (2) The capacity of a.main is ntil- ■ ised throughout tho twenty-four hours, consequently a main'of smaller diameter ;., may. be provided. (3) A considerable stor; .;; age is available -. in the .city . in....'.' the event of damage ■ to the, trunk, mains, caused by earthquake, floods,;etc ~. 'A) During time of floods ,the water is of tetter-quality owing to the settlement of •- solids in suspension being possible in the reservoir before the water is drawn into' . the reticulation system;!' A-connection . between the supply and delivery pipes at ,• the distributing reservoir should ; bemade as a by-pass when the reservoir; is out ■ of use for periodical cleansing. Cost of the Scheme. • Mr. Morton estimates the total cost of the work at .£79,680, made up. as. fol- J lows:-r ' _' .' ' '~. 360 chains, 21-inch-'.'....»........'....••». 62,408 GO chains, 15-inch ...........: 3,880 Bridges over Wainui ..;............... 409 Distributing reservoir 12,009 Engineering and contingencies ;.. . 2,008 ; Total .....:.:......£7?,680 In arriving at the estimate of cost, it. has been assumed that a cast-iron main will be used. The engineer considers' . that on the whole cast-iron, is .preferable to steel, but alternative tenders might be called. . .' Another Catchment Area. ; Mr. Morton mentioiis the advisable-!_' hcss of obtaining information" whether ',\: at any future time the Orongorougo Stream, or a portion of it, can be turned : \ into the Wainui Valley. He advises that tho Government should be approached with a view to setting apart the Orongorongo catchment area 'permanently as a waterworks'reserve. : .In. conclusion, lie observes: "Experience- of. other/cities shows that it is almost impossible to look too far ahead when dealing with ques- . tions relating to the water supply of the city, and although no necessity for obtaining further supplies is likely to be experienced for a considerable number of years, it would show serious want of foresight, when the time arrives for further supplies,, if* the catchment. area re-, ferred to had passed beyond the city's.'coutrol. I strongly recommend' this proposal for favourable consideration."