THE CITY'S NEW SEWERS.

New Zealand Herald, Volume XLIX, Issue 14927, 27 February 1912, Page 4

THE CITY'S NEW SEWERS.

BURROWING UNDERGROUND

AN ENORMOUS SYSTEM.

MAIN LINK OF NINE MILES

A TRIP THROUGH THE DRAINS.

Wnn.K the fact lias been fully impressed upon every open-eyed citizen of Auckland that a drainage system of magnitude is in progress of construction, it is true that very few have any adequate idea of the huge extent of the system, and of the large matters which depend directly upon it. A town built upon hills has an obvious makeshift drainage, compassed by simply conducting its sewage to the gullies and natural waterways. There it will establish itself until expediency compels tho installation of some more or less elaborate method of control. Befoie very long in the development of a town the original crude drains disappear to make way for sewers; and these may or may not be so arranged that ill later they may be linked up into a single system. But more often than not, each gully sends out its pipe to discharge on the nearest waterfront, and to provide a problem to unborn engineers. Such a development is always apt to leave some hollowwherc the primitive system of drainage pollutes a trickling stream, and spreads a feverbreeding effluvium in the neighbourhood. Present-day Drawbacks. Auckland has reached beyond that stage now-. It has its range of sewers, all leading out into the. Waitemata, at intervals from Ponsonby to Hobson Ray. and all polluting the fair inland water. It has one waterway —naturally a pretty streamlet—which sewerage has converted into an offence in the ArchhQl gully. The' drainage into the harbour is perhaps not so great that it need be regarded as very offensive at present: but the Arehhiil gully is a good example of tin attractive stream alienated from all human friendship. The present method of many independent discharges necessarily forbids the city from generally adopting, as it would otherwise do, nn up-to-date sanitary system. Much of tha effete material of Auckland has to be disposed of by other means than sewers at present, though proper sewers are recognised as the best means for scavenging all except combustible or indestructible materials.

Working a Revolution. The new drainage system, which is being built and dug and fashioned with skill and elaborate labour, is to effect such a revolution in the sanitation of Auckland as will introduce a new era in the city. There will be no discharge of foul waters into the waters of the Waitemata, which will be of a fine sweetness. There will be none but limped water in the Archhill gully, where the watercress will be eatable again. There will be, in thousands of acres of residential lands, no offensive .makeshift removal of what can well be borne away by water: and no excuse for the propagation of any of the diseases that flourish in filth.

Men are burrowing to-day beneath the streets and houses and parks of the. city. They are busy in many places with explosive, and pick and truck where they have burrowed ; others follow with concrete and bricks; and daily under the city and suburbs there is growing a huge veitiing. In the end there will be a main line of piping, which will start from close to Oakley Creek, beyond the Mental Hospital, and will pass irregularly through and tinder the frontal length of Auckland, cross Hobson Bay, and end at Orakei. From it, on one side or the other, will be made 13 branches, some short, some long; and the main line is over nine miles long. The casual citizen who sees the drain outcrop here and there in low-lying parts of the city, or watches the operations of the men at winding heads here and there on hillsides, has little conception of the great work those small signs indicate. The Drainage Board's Aims. The Auckland and Suburban Drainage Board controls an area of between 15,000 and 17,000 acres. It contemplates a population within the capacity of its sewage system of over quarter of a million people. To carry out its works it has power to expend half a million sterling. A huge sum. this, to be buried in the earth in the form of concreted boles and huge conduits over flats and hollows; but the work is huge, too; and a survey of it, even casually, reveals unsuspected difficulties and complications, which make the building of a great drain a task for skilled engineers to supervise and for a host of experienced workers to carry out, and which all add to the cost of',l '" straight job." How the System Will Operate.

The theory of the Auckland drainage system is simplicity itself. A main line and branches stretching into all partis of the drainage area- when- it. is necessary to give convenient access to the local reticulations, passes out to Orakei. where the pipe debouches into a vast tank. Therein the sewage of half-a-day stores up, and shortly before the tide 'readies full high water, the escape is opened, and the whole contents discharge into the sea. Careful experiments with floats have shown the responsible engineers that, with the discharge effected at the right time, the sewage will, at the turn of the tide,' commence a rapid march oceanward. and be carried far away past Rangitoto, to be lost in the immensity of the sea. An enormous volume of water runs from the Waitemata with the tide; and the sewage flowing from the outfall will be so enormously diluted that it must be quite harmless. The open sea is the e-reat cleanser, and cannot be. 'polluted. But to carry out this simple scheme is no trifling task. It involves devoted attention to de" sign. a full exercise of the cunning of a specialised engineer, a watchful eve upon the emergencies which must occur when designs are based upon many unseen elements. A host of men under many masters, a vast quantity of raw material, and the intricate time-tabling of all sections of the work, all come forward to demand supervisory attention; and when all is arranged for and working in full swine- the task of providing the city with new veins has become stupendous. A Survey of the Work. A Herald reporter a few days ago made a tour ot the sewage system," tinder the guidance and tutelage of Mr. T Mae harlane. A start was made at the'outfall at Drake,, then the main sewer-line was followed tip to the city, with diversions to inspect the branches which join it- and afterwards a flying visit was made to the system lying in the western part of the drainage area, to gather some idea of its extent. Jhe first- work is done bv the surveyors, who spy out 10 land and collet vast quantities of data, as to contours and heights, and levels. Their information is passed over to the engineers of the scheme; and the building of the sewers may truly be said to commence in the Drainage Board's office. There the orr-i neer plans out the broad lines of tho scheme; and day after day the outline and then the lesser and , lesser details take shape upon huge sheets of paper. The I whole success of the system depends upon the accuracy of the drawings, once the designer has his ideas set out aright Then may he considered the surveyors who with theodolite and tape set out upon the surface the lines of the work. Running their measures over the surface and peering here and there through their 'little telescopes, they fix an imaginary but quite definite and calculated line in tho solid earth, for the navvy to follow later. When the actual work of digging begins the surveyor goes down below, and retraces his fancied line, while the men dig awav the rock from about it.

Then come, the contractors. These airmen experienced in the practical side of constructive work, and they attend to the

multitude of details that otherwise would have to bo the care of the public body controlling tho whole work. They and nearly 400 workmen do the digging and building, directed, like armies in tho field, by the executive in the Board's rooms. And the ratepayers, who have authorised the work and have to pay for it all, sit about and know little or nothing of what is going on beneath them for their comfort.

The engineering difficulties of the drainage problem can be indicated by the fact that the extreme upper end of tho ninemile stretch of main sewer is only about 30ft higher than the Orakei end, and that hills and gullies, existing watermains, and rights of property-owners notwithstanding, an even slope has had to be provided for from one end to the other. A fall averaging 3ft in a mile is not a considerable matter, and gradients had to be nursed to give a proper rate of flow in the long channels; yet more slope could not be provided without cutting out parts of the drainage area which would have been too low to use the sewers. This, of course, has necessitated careful surveying. The accuracy which the civil engineer practices in the handling of his large measurements is so much a part of his business and training that the wonder of his aiming successfully at a given point a mile away hardly appeals to him. He tunnels complacently from two distant points, mapping out his course as he goes: and the two tunnels surprise and annoy him if they do not. meet and coincide within a few inches. How the Sewers are Made. The actual process of sewer building varies according to the size of the sewer and according to its position. Within the 1 bounds of Auckland nearly all the sewer line is well underground, and most of the conduit is of large size, so that the method herein conies under one description. In all tunnelling much the same work has to be done; and the work is pure mining work. Where the sewer is to be large the. tunnel is cut just large enough to contain it, allowing, of course, a margin for irregularities. When the sewer is small the tunnel lias still to be made large enough to allow men to work freely within. Remarkable Tunnelling. The rock is bored by drilling carefullyplaced holes, putting in explosives, and blowing out masses which, under skilful management, leave only trimming to be done to make the tunnel the right size and shape. The accuracy with which the material can lie blasted out by skilled miners is indeed remarkable. The spoil is removed by shovelling and trucking it either to the end of the drive, or if that is not within convenient distance, to a shalt, where winding gear is fitted and a more or less elaborate enginehouse established. A good deal of water percolates into the workings, and needs either draining or pumping out ; and it constitutes a serious obstacle to easy work, and adds greatly to the unpleasantness of the operations. Fortunately. Auckland rests upon a bed of material admirably adapted for tunnelling. In all the length of the sewers only a few trifling patches of loose and untrustworthy ground has had to be pierced; everywhere else the soft sandstone has yielded kindly to the explosive and the pick, and cutting freely has yet "stood up" without more than trifling aid from timbering. The Lining of Sewers. - Various methods of constructing sewers are in use in the tunnels. Sewering of moderate size is made by laying down on the bottom of the tunnel a foundation of rough _ concrete, and bedding upon it a row of concrete blocks to form the bottom of the sewer channel. False work is placed upon (lie blocks, and concrete is thrown outside it ; and when the false work is removed in sections the lower half of

the sewer is revealed almost finished. Other false work of semi-circular form is then put in to form the top arch, and this is built of bricks, .specially moulded, or of concrete blocks: and •remaining space between the bricks and the sides and roof of the tunnel is firmly packed with pieces of stone.

Ihe huger sizes disnense with the I moulded blocks at the- bottom, and the , whole lower half is made by pouring eon- . Crete round the curved false work. In > some places the sewers emerge from the ; tunnels, and there they are wholly of . concrete, and where the circumstances de- - mand it. of reinforced concrete. f The facility with which the building -. operations can be carried on depends much 1 upon the size of the tunnel: and in the case of small sewering the contractor has to decide upon some size of tunnel at which there is a* happy balance between the cost of excavating and refilling extra space, and the inconvenience and loss of ' time that would be caused by making the men work in a space too cramped for their bodies. Even in the larger parts many of the operations have to be carried out with no room to spare; and the conditions are ' very awkward in the "upper reaches." The sewers underground, once finished as far as the building is concerned, need little further work upon them. The method ~t construction leaves the surface moderately smooth, and a little attention by chipping, grouting, and washing with cement is sufficient to make a good finish. Where the workings traverse verv wet ground there is a good deal of " weeping. ' the water oozing slowlv through the lining; but, that is curable. ' The Hobson Bay Sections. The sewer emerges completely into the light ot day 011 the Parnell side of Hobson Bay; and its huge pipe, striding 011 piers across the bay in two long reaches is a most prominent feature of the landscape. At Uhakatakataka Bay is dives under part 01 the Orakei reserve, and then sweeps m the open round Okahu Bay to lie huge, storage tanks. The crossing of Hobson Bay has been effected bv driviiv piles into the mud bottom, often to verv great depths. An ingenious but simple ] device enables a working platform to be made just about high tide level; and the sewer is constructed wholly of reinforced concrete. About half the length of this port!"" of the work has been completed and the work is in progress in sections. ' Bound lOkahu Bay the sewer forms a handsome sweeping wall, as it lies half buried in the sand of the beach, and it denies the lino of the bay with a graceful curve 1 ♦ But for the sentimental* objection that it is a sewer it mac be fairlv regarded as an acquisition l " the landscape. J his part ot the sewer, and that whK passes underground to Hobson Bav, are quite finished. The Okahu Hay portion illustrates one o the difficulties of eon crete work. Uhile the lower part of the sewer is buried in .sand, and mSi, ah san almost unvarying temperature, the upper """■I is exposed to the hot sun, and i has. as was inevitable, cracked The curve of the line could not save it, since £« heavy sewer is so , efficiently anchored in sand But the cracks, while numerous are. small and unimportant, and thiv S ['rib," the least likely to cause' any j The Huge Tanks at Orakei. ! An enormous undertaking is the con- I ilruclion of the great storage tank, which : moment fu the «**■«• ™ tS "ho moment for its discharge into the sea. It « st treble reservoir, quart6r of » »ilo long, built wholly of concrete At pre « sent its outer wall has been finished the : ben; , :ie;-eii;r n f huilt ' andti,eb ' ■ floor? late ♦» t0 £0" wails concrete 1 liooi j Jd tei two interior walls of rein- ' forced concrete will be built, and a err concrete roof nut over ll - forming inciS"uf at a tue o e n cJ (letdl ° f "W* 1 bers, so thai the ta iks can'bof Urf * desired order. VVhen £ tid!"fa S,„ , be opened, and the v»st ™„ , Ui t J a/S;e^l,lES. h J iron cradles, fixed into Sesfn the not" * torn by concrete, and obviously °uch work J can only be- done when it is calm

Side-tracking Storm Water. There are many interesting details to study as one traverses the course of the great drain Among them are the "overflow tanks," placed where the branches join. I ho duty of the sewers is to carry off every day the foul outpourings of the

■" city and when it rains to provide a proper escape for as much of the storm water as possible. If all the storm water collected by the i branches entered the main sewer it would be more than filled, though it is Bft high and over sft wide. Moreover, sewage diluted with an enormous proportion of rain water is so innocuous that it can safely be discharged in an emergency into an open watercourse or into the sea' without giving offence; and the overflow chambers provide for the superabundance to be discharged by an auxiliary path. Their method of operation is quite simple. In a typical instance, the branch sewer leads into a large concrete casing placed near the main sewer, and discharges into a small trough. From thus trough passes another pipe leading into the main sewer, and of a size to take only the maximum quantity to be allowed to pass from the branch. The trough is so adjusted that when the amount flowing in it is more than six times the normal flow—at which degree of dilution sewage is accepted as being inoffensive—it runs over the sides. The overflow falls to the bottom of the chamber, and finds an opening into another pipe, which leads directly to the sen. These chambers are such a simple device that they are described principally to show that, large as the sewers are, they are not; and could not with reason be, constructed of a size to carry off all tho storm water which runs from the vast drainage area. On the other hand, it must not be supposed for a moment that, they are in any way too small for the ordinary needs of the city. They have been calculated for a population far greater than is at present in Auckland, and eVen at the calculated normal capacity the largest pipes will only flow about 3ft deep, and the smaller ones will bo filled to a height less than proportionate. Thirteen Branch Sewers. There are 13 branches to the main sewer. Only one, that traversing the Archhill gully, is finished. It is about two miles long. No. 1 branch, which runs from Wilson's point, in Hobson Bay, along a general curve to Greehlane railway station, a distance of well over two miles, is almost finished. So is No. 3, which comes from the junction of the Epsom and Great South Roads, beyond Newmarket, and joins the main sewer on the Parnell shore of Hobson Bav. No. 2 branch, which roughly follows ' Portland Head into Hobson Bay, is in hand: and No. 3a, along the Parnell shore towards Resolution Point, has' also been begun. No. 3b is another small branch near St. George's Bay, and is under construction. The No. 4 section of the main sewer runs from the Grafton Road entrance of the Domain, under Albert Park to Vic-toria-street, which it follows: and branches 4a and 4b are small curved appendages commencing the one near the Domain entrance, the other at the corner ot High and Victoria Streets, and with Government House as centre roughlv following arcs of a circle till*they almost meet. these branches, with No. 4 section of the main sewer, have been begun. Branch 5 will leave the main sewer at Nel-Son-street and sweep round the seaside of Ponsonby to beyond Heme Bav; and its construction will be commenced almost immediately.

,1 r Ijiillicit No. 6 IS a small one. skirting] Cox.« Creek, and will serve the south" " western portion of Heme Bay. There are two small secondary branches to No. 7 one to Kmgsland, the other to Edeii terrace, •s 1 0 ' 8 , branch will he about two mile; if and *'1:'"™; long. It joins the main 11 ',V U ? 1,1 T ? Ieo ! a Creek, due east from the lf .Mental Hospital, and follows the Meola a {X r . et , a . n ems a ' *' ie junction of Mount n « ifn . «™°ugh and Mount Albert and s -Mount lioskill I toad districts. It will s serve the area included in the basin bek ,^' een -V.°«nt Albert. .Mount Koskill. and ,f llireo Kings, and extending to the- Mount _ Albert and Epsom Road. * The Notorious Archhill Gully. ' , Some special reference must, be made t< ■ J l,O .Archhill Gully ewer. It is No. 7 ' * branch, and from its junction with the h !»™ www near the old citv abattoirs it lows up the gully almost to Newton • itoaij. it- has long been finished, and | could by this time be in use by all the * area it JS intended to serve, if'the local : bodies concerned had made the connec- ■ tions necessary to avail themselves of it Some of them have done so. Temporarily the branch opens into the lower end oi r ,I|C S ul 'y- *" that the sewage finds its ] May to the sea by the ancient route ; but > he aim of the Drainage Board has been , to convert, a pestilential watercourse to a ! cleanly one as early as possible. It is not their fault that the conversion ha« been only partially effected. The gully is far Iron, being as offensive as it was, _ though short stretches still betrav its ; awful possibilities , The little creek belonging to the old ■ j watercourse is itself attractive enough; and apart from the drainage the gully is in many ways charming. As soon as*the sewer is in full use .some at least of the people ot Auckland will find a- beautvspot in a. place where they have been Used to hold the nose firmlv and to fear j zymotic disease. j Along the Main Sewer Line. j The. greater part of the main sewer i.< j of Jar larger size than most, people would ( imagine J' or fully six miles, a tall man could walk along it with ample headroom, j Over two miles of it. is over eight feet in j height ; a ■similar length ranges from 7ft Jin to 7ft 9in in height; a mile or so is bit 9m from bottom to top. There is roughly a mile measuring 6ft high • another sft, high ; and the tail end is a' section 3tt 6in high. The pipes are nearly all egg-shaped, with the small end at the bottom. This form ensures that even a small quantity of sewage will have it sufficient depth to give, a fair rate of Mow anti yet provides a large capacity lor the exceptional demands ' of stormy , weather. If the pipe were, circular and of the same capacity, a small normal flow of sewage would he shallow and sluggish and the sewer would not keep clean ' | The ample dimension:; of the main sewer for the greater part of its length make a tour of inspection, for the most part, quite easy, though it is a messy undertaking. The sewer is, of course quite unpolluted as yet bv its destined purpose: and the finished'tube is easily entered and easily traversed. The portions under construction are not. so easv to negotiate. They are dirty and wet and where the building of the conduit is in progress they are obstructed bv the temporary fittings. In the tunnel's one has to bob the head to avoid bumpiii" it on a. beam, put down the feet warily on the irregular, muddy, and submerged bottom, and hold a flickering bit of candle with jealous care. Gum boots keep the feet dry. and overalls preserve the clothes from the dripping wet and tho muddy walls. Among the Workers. The visitor to tho sewage works at this j stage meets with at least two experiences of special interest. On the one hand ho finds himself among tho men in the halfbuilt sewers; on the other bo stands lonely in the completed, silent tube.. The lot of tho sewer-builder is the lot of a digger in an uncomfortable place He works by insufficient light; even the acetylene lamps in use give but a localised illumination, though it is many times bettor than that of candles. For part-of the timo at least, ho is oppressed by the fumes of high explosives, not vet' thoroughly cleared out by tho mor'e or less efficient method adopted to ventilate the tunnels. In some cases the method is distinctly inefficient. In much of the tunnelling he paddle? about all day in sloppy mud; and if the contractor 'is a careless provider, tho board track apologises for its absence rather more than it should.

The men work often in cramped attitudes, ft work that is- anything but li.'.ht •' they can pass backwards and forwards' as many of them have to do constantly-' only by continually " ducking" to avoid beams overhead, and by keeping attention upon their feet m the pug gy or s]opp mud. There is no questioning that a man who fills his day with toil making a sewer earns to the full the shilling that go to his credit. b

In the Silent, Finished Sewer. The impressions of a neophyte in a finished sewer are not alarming,'but thev are undoubtedly peculiar. He enters by a manhole—manholes, by the- way, are few and far between cine© so much of

the sewer is far be-low tho surface. He walks a few feet, into a- darkness that is utterly dark, and into a silence that is as dark and heavy as tho absence of light. In that long tube of concrete there is nothing else living, nothing moving, Then suddenly, a yard away, or ten, or perhaps a hundred—he cannot tell, a drop of water falls from the roof into the long pool in 4fce bottom. The little "plop" is instantly followed by a din of echoes. It starts off with a ringing sound, almost shrill, that gradually lowers in tone until tho whole long tunnel seems to be full of a fading note, deep in the wale, that finally dies sadlv away. In the depressing silence the visitor dares to cough; and the cough flies away and comes hack overwhelmingly. Its echoes hoot and grunt at him, and wash over him in surging waves of sound, and leave him astonished. It is not surprising after such an experience, to learn that men can converse with ease between the ends of half-a-mile of the sewer.

None of the conditions induce one to stay long in the finished sewer. One quickly develops an uneasiness lest a miracle should fill the great tube with a swirling, hurrying stream. One fancies the bitter fate of being borne along, looking for a friendly man-hole in the distance and its attendant iron loops, waiting to be seized : and then trying to seize them, and missing. A few "moments of such imagining develops an automatic motion by the feet towards the manhole that is really available; and in a few minutes the eyes are blinking in the sun and the struggle to take off unaccustomed sea-boots has begun.