THE "O.K." MAIN

Evening Post, Volume CX, Issue 102, 27 October 1925, Page 5

THE "0.X." MAIN

REACHING OUT TO CITY

BUT A LONG WAY TO GO

THE BENEFITS TO. FOLLOW.

The ■ Orongorongo tunnel is an accomplished fact, and the possibility of short commons in the city water supply is greatly removed, for by operating tho length of new main through' the tunnel to deliver into the Morton dam and the smaller Wainui dam these storage reservoirs can be kept abundantly full, unless it should be that the Wet-, lington district experienced a record drought. That, however, does not represent the full usefulness of tlie Orongorongo supply: during several summers past, even last summer, when tlio Morton dam maintained a good level, difficulty has been experienced in supplying certain of the higlier-levol localities iv the city, simply because Ilia pressure in the two mains serving the city was insufficient ■to force the Miiter up to those localities, and because the Karori reservoirs' were pretty low right through th-j winter and into the summer. The old school-book rule that water rises to its own level-applies in a general manner to a city's water supply, except |hat frictionnl losses and other complications must be taken into serious account when roughly 20 miles aru travelled by the water. Tho higher the intake point the higher .may be tlie delivery point, and, on the whole length oi' mains, the greater the pressure, the old Wainui reservoir is 406 feet above .sea level, the Morton dam 457 ft, but tho intake, for the new main in the Oi ongorongo Valley is about 800 ft above sea.level, a very considerable difference.

WHERE KARORI COMES IN

High prcssnro is not the only consideration; the maintenance of steady pressure is of equal importance, and it is in this regard that the Karori reservoir comes in, and for this reaso:i that tho new main, the "0.X." main, runs from the Orongorongo intake to Karori and not direct to the city scK'icc mains. Tho now maiu will deliver to the lower Karori dam, 4(i:!ft above sea level, and from that reservoir the water will be distributed to tho city. This pressure will be steadied,, an additional storage of many million gallons will be given tho city, sufficient to tide over days spent in repairing mains should something go ; wrong, and better service will bo Sgiven to higher levels. At present tho Karori ■ storage is dependent solely upon rainfall on its own catchment area, and past experience has shown that that rainfall is not '■Ui be felled lipbn. The 'higher pres"isuro in the Orongorongo-Karori main —when it is comploted^-will also make possible a direct supply to thd now reservoir built for Onslow (720 ft) iiiul to a small high-level reservoir for Karori Heights (720 ft), to which points water is not at present supplied. Other localities will also bonoJit, and over and above consideration of better pressure and extended supply will be the provision of another direct main, that bursts and blow-outs may be a less serious matter;

WORK SPEEDING UP

Yesterday a party of about a dozen' was conducted to Waiiiui and Oroiigorongo by the waterworks engineer (Mr. J. M. Moricc), and the points of interest explained on tho spot. For. a long time after the Completion of the tunnel, in March, 1024, the supply of pipes to join up with tho Karori reservoir hung fire, but now the supply has settled down in steady fashion, and great steel pipes, 21in in diameter, line tho roadside across tho Wainui flat ready for laying and jointing. About three miles have already disappeared in the hand-cut trenches down the valley below the reservoirs, and each day the mechanical trench-digger'crawls nearer the city by about a quarter of a mile or more, The going suits it admirably, straight ahead in heavy clay, rather more soggy thaii makes working pleasant. Big stumps are frequently met with, but steel cutters with power behind them do not stop for wood when properly handled. A- solid snag may give trouble, but it does not spell disaster.

When tho flat is trended the pick and shovel will come ill again over the difficult Waiwetu climb and fall, but onco over the hill tho mechanical diggers—a drag lino digger as,well as the rotary cutter trencher —will come in again over the river flat 'and-the five-miles of the Hutt load. The digging of these five miles may present' hard going" to the machines, for the road foundation is recognised by the engineers as being well and solidly laid. Trenching and pipe-laying is proceeding also from tho Karori end.

•Statements as to when the new main will bs through aro not made freely by those- in char-go.of tho work, for there are delays in variety which may interfere with the regular and s-peedy prosecution of tiio work. AVulJington may not have the full benefit of . tho 118 IV supply this summer, though tho danger of a water shortago is practically fully removed, but the following summer should certainly sec high pressures where low pressures are to-day complained of. a regular supply to thoOnsloU' district, and a. full supply to Karori. in which localities tho street reticulation is completed, and in which the work of laying drain ago. services is going ahead steadily. Probably the now main will be through well' before the summer of 1920-27, but when engineers do not commit themselves it'is wise to mention an outside date rather than a desired date.

To drive ,i: three-mile tunnel through stubborn rock, to handle a mountain stream given to roaring Hoods the wliolo year round, to trench and lay and securely joint thirty-foot steel pipes over twenty miles of country, a good deal of it difficult country, is not a task to be magically completed in a month or two. There have been delays, some of which might have been avoidable, and those delays have meant a loss of money as well, as of time, but to-day the work pushes ahead steadily to completion.