DUNEDIN DRAINAGE SCHEME

Otago Daily Times, Issue 13996, 31 August 1907, Page 5

DUNEDIN DRAINAGE SCHEME

THE MAIN OUTPAT.T, AT LAWYER'S HEAD.

• COMPLETION IN SIGHT.

The extension of the gravitation outlet at. Lawyer's Head—that is to say, tho construction of tho main outfn.il of a drainage system the main artery of which is already ™ flown—is, as tho actnal construction work is ooncerncd, practicably completed.- The 860 ft of main tunnel has boon driven, the huge air shaft, 103 ft in depth, has beon completed, and tho two bifurcations, the eastern one 171 ft in leugth and the western 86ft, lmve been driven their full distance. All that now remains to bo done is to lino tho huge length of tunnelling and shaftinp with 9in of concrete, burst open, the thin wall of rock at the terminal points of each bifurcation, and Dunedin has its drainage outfall completed. Thero has, however, been a big difficulty to contend with in tho construction of the ma.in drive,-, and that is now being 6uroly and expeditiously overcome. About 120 f- from tho air shaft tho main drive finds its courso through a cave which extended into the cliff for,- a distance of 6omo 90ft and into which tho soas break with 6uffioient violence to smash up tho 60wer within a very short, period wore-it left unprotected and exposed,to tlieir force. - It has beon decided to take no ri6lre at this particular spot. The cave, a short distanco from its mouth, and where it tapens oil considerably in height and width, is to be completely, filled up wiih spalls and cement right back to the wall of the sewer. Preparatory work in connection with this Iras been in hand for a week or two, and it is expected that a fortnight further will seethe . work -. completed. So far a hugo barricade of Heavy ironbark timber has been placed within some feet of tho mouth of the cgve, both ends being firmly wedged into each of the walls. This work is being performed under very great, difficulties, and can only be carried on according to tho whims or vagaries of tho tide. In fact the oa.ve referred to, intercepting as it does tho main drive, has on sovcral occasions been a source of very considerable danger and delay. The heavy seas that were experienced a week ago broke through it, and threatened to fill tho cave, and did do so almost completely for some hundred of feet. Tho men had consequently to be removed and work suspended for the time being. A Times reporter was on Wednesday very courteously guided over the whole works by Mr A. Stinger, tho Drainage Board',?, engineer.. . The. huge .air shaft whioh has been sunk almost on tho site of the old battery on the summit of Lawyer's lload was first entered, and a descent made, by means-of a series of ladders, to negotiate the landing at the foot of each and their supporting wooden pillars necessitating the executing of some rather extraordinary bodily contortions. To make matters .worse, "tlio shaft is darkness itself. At the foot, about 100 ft down, it broadens out into a chamber that, when completed, will bo. about 22ft in width and about 15ft in height. From each side of this chamber the two bifurcations branch off, one'to'tho oast and one to the west, and both .taking a gradual sweep-in arid forming whafr is practically a complete half circle. So constructed, the heaviest seas can break in at either end, and with tho sweep • that the bifurcations tako find a natural course, and not hurl themselves against any portion' of the construction worl;., ,Jiist ,171 ft, through the eastern bifurcation precisely meets the cave, which extends' into the cliff on that side for, Mr Slinger estimates, fully 120 ft. The sttiking of this oave in so accurate a manner, must be regarded as an eminently satisfactory pieoe of work. Likewise tho bifurcation on the western 6ido of the head. ' A hole about a foot in diameter has been pierced through near tho floor of the eastern bifurcation, and one can look down into the cave and see the waters surging and boiling at each suocessive inrush. The noisi is almost deafening, and the inky darkness, which a lighted cajidle almost fails to penetrate, adds to the general weirdness of the scene. When a more than usually heavy sea breaks into the cave it shook, or, rather, is belched through.the small vent at the invert of tho bifurcation with an awful force, adding to the deafening noise and flooding tlio drive in the vicinity with a deluge of water. In the western bifurcation tho smaller cave there, about 70ft long, has also been located within an inch, and- there remains only about 3ft of eolid rock to be knocked out to connect the tunnel with the cave. In the ease of both bifurcations the few-final feet of solid rock will not be broken through until the whole of tho tunnelling and shaft has been lined with ooncrote, for once tho intervening wall of rock is broken through tho sewer will bo quite'impossible of ingress. The invert of both bifurcations is at high-water mark, which will mean that thoy will always discharge at high-water mark, with at low tide a drop'of, say, 6ft at tho least.

The contractor for tlio construction of the 'whole of tho work is Mr "Angus M'Noill, and it must lie said that, allowing for the'unforeseen and almost insuperable difficulties to be contended with, excellent and steady progress has boen made toitlv tho work. Tho job is going to bo' a thoroughly good one, aad on that tho publiocan rest assured. "I am going to push" tho work through," said Mr M'Neill to a Times reporter, "and have tlie work entirely completed bv Christmas. Onoo wo start on the concrete lining of the sewer and shaft, work will bo carried on: night and day. Wo would have completed tlio piercing of the bifurcations threo weeks ago had it not been for tlio heavy seas coming into the drive through tho. cave, which intercepts it, compelling some of tho men to cease work for about three weeks. , The striking of that cave in tho middle of tho driving has caused considerable, extra work and delay. But I must say that every oredit is duo to tho 18 men I have on the work. They hive stuck to their work Tieroicailv, even when at times deluged with water. These men wero formerly working on the abandoned tunnel which runs in the direction of '.tho Tomahawk Beach, and on the starting of ■ this contract some of them camo from as far away as the North Island to take up the work again. I myself, and the men also,, could not wish to work under a better man than Mr Slinuer. So soon as the excavating of the chamber at the foot of the shaft has been completed the concrete lining will be started on, and' I expect that will bo in a fortnight's time. Christmas will see the whole work oomplcted."

Sincc the commencement of the contract in February of thi6 year 6otno 25001b of explosives have been used in blasting operations. The carting of metal and eand for concrete purposes to such a remote place is naturally a heavy undertaking. The 300 ft of ' abandoned tunnel which formed part of the Bird Island schemejs throughout, filled to a depth of about 3ft with the clearest spring water, and this will prove of immense saving in the mixing up of the concrete, of which a very considerable quantity will bo required. Personal inspection only can give any idea of the magnitude of the work undertaken, comprising as it does the sinking of some 100 ft of shaft and tho driving of over 1100 ft of tunnel.