THE BIRD ISLAND OUTFAIL

Evening Star, Issue 12027, 27 October 1903, Page 4

THE BIRD ISLAND OUTFAIL

A VICTORY FOB THE DRAINAGE BOARD. [SjMCCIAIi TO ras Stab.] WELLINGTON. October 27. The report of Commissioner Carew on the question of the discharge of sewage at Bird Island reached His Excellency's hands at ttie end of last week, and has just been returned to Cabinet I have to thank the Minister of Works for being supplied -with a copy of the same for irmnediate publication:—

May it please Yoar Excellency:— I have the honor to acknowledge receipt of a communication under the hand of your Excellency and the seal of the colony appointing me to be a commissioner in use matter of a proposal of tfc© Dunedin Drainage and Sewerage Board, seeking authority to carry out works for the discharge of sewage from the City of Dunedin into the ocean at Bard Island, bo -which works objections have been made by the Tomahawk Road Board and the residents of the neighborhood,, and directing me to hold an inquiry into the advisability or otherwise of authorising the discharge of such sewage at Bird Island or adjacent thereto, having regard to the extent {if any) to which such discharge is likely to pollute the foreshore, create a public nuisance, or cause danger to the public health, and thereby dt-teriorate tie value of property m the neighborhood, and if it is considered inadvisable to authorise its discharge there to report as to where I consider the discbarge into the ocean might reasonably be made, having regard to the consideration aforesaid. I am also instructed to report my several proceedings in this matter and my opinion touching the premises.

I have now the honor to report that I received tie commission on the 11th ultimo, and oa the same day gave, written notice to the secretary of the Dunedin Drainage Board, to the chairman of the Tomahawk Road Board, and to Mr Alexander Barron and Mr John Robertson, the gentlemen. first-named in the petitions of the residents of Anderson Bay, HighdifL and Sandfly Bay respectively, informing them of my appointment, and that I would be ready to commence tie inquiry at the courthouse at Dunedin on the 15th September. On that date Mr White (solicitor) appeared to represent the Tomahawk Road Board and residents of Anderson Bay district, and &r Sim (solicitor) to represent the Dunedin Drainage Board, and they have so acted throughout this inquiry. Arrangements were then made for the conduct of the proceedings and the examination of witnesses. On the 22nd September I visited Tomahawk Beach and Tomahawk Cliffs, in company with representatives of the Drainage Boar-i and the Road Board, and gave my attention to sach matters as they brought under mv notice. Evidence was taken on sis: days. Ten witnesses were called and examined by Mr White for the Road Board and residents of Anderson Bay; ten witnesses were called and examined 'by Mr Sim for the Drainage Board. Mr Hales, the engineer-in-chief, was a witness bv desire of both parties, and Mr W. D. R. M'Curdy, the district road engineer, volunteered to be a witness, and was examined bv both parties.

The matter in dispute is dearly and concisely put by the enginear-in-chief to the Hon. the Minister of Marine in. his letter of May 29, 1903. He says: "I find that it is proposed by the Dunedin Drainage Board to locate the outfall for the City sewage sj stem on Bird Island, which is a small reeky islet, situate near the eastern end of Tomahawk Beach, about 23 chains ont from high-water maik on the beach, from which point it is intended to convey the sewage matte T in a 40in diameter concrete pipe syphon, supported on a bed of concrete deposited on the solid rock bottom below the surface sand, and covered over the sides and top with a strong Layer of concrete, and further protected from the action of the waves by heavy rubble deposited along the sides, and discharge it into a basin about 20ft diameter excavated out of the solid rock on the top of the island about lit above the level of high tides, when it will flow off by specially-prepared outlets into the sea, and is expected to be carried clear of the land by the local currents flowing around the island, which are said to set offshore at this place." It is claimed by the chairman and members of the Tomahawk Eoad Board and other residents in the locality that if large quantities of sewage are continually - discharged into the sea at Bird Island, as proposed by the Dunedin Drainage Board, a very considerable portion of this_ sewage matter will,, instead of being carried out to sea by the currents, be driven onshore by the waves, which are always running in towards the share, and in stormy weather break heavily ewer the reef and on to the sand beach, with the inevitable resalt that the sands of the foreshore over a considerable area will in course of time become polluted by this deposit of sewage to such a degree as- to be a source of discomfort as well as danger to the community. I find from the evidence of Mr Anderson, the engineer of the Drainage Board, that the discharge at the proposed outlet into :he basin is expected to be four millions of gallons of drainage per diem, containing one million gallons cf sev*age; that the sewage at the point of discharge will practicaitv contain no solid matter; and that the largest proportion of solids under similar systems of opposing of drainage where it is elevated by pumping and consequentlv churned and broken up consists cf chips of wood, corks, and human hah-; that the liquid is a dense black color when it first issues into the tx&, but fifteen or twenty chains awav nothing of it can be detected.' As the character of the discharge is an important clement for consideration, I quote the following from the evidence of Mr Edwin Cuihbext, engineer of the Christ-church Drainage Board :—" According to my experience m Ghi-istchurch, sewage treated as is proposed by Mr Anderson would be discharged in an almost liquid form at the outfalL There might be small particles of fat the size of shot floating. The proportion woidd be very smaJL so small as not to be worthv of any The effect of having a combined system as Mr Anderson proposes would be to make sewage more dilated with clean water." Mr W. A. Smith, assistant engineer of the Drainage Board, and a Bachelor of Science in Engineering, eays (page 42 of the evidence) he had had opportunities of observing the discharge of sewage, and in his opinion the sewage at Bird Island would be discharged in a perfectly liquid state—that is, as far as the sewage itself goes, but there might be particles of fat. The evidence of Dr Black, Professor of Chemistry at the Otago Universitv, i« that from the excrement of a population of 60,000 there will be about 500 tons of insoluble organic matter per annum, some of which will sink and some keep afloat suspended. This will be the most objectionable portion of tiie sewage, and it has to be remembered that this quantity will be contained in about 1,400 million gallons of sewage. The evidence of several witnesses for the objectors, long resident in the district, proves that large quantities of seaweed and floating matter is deposited en Tomahawk Beach, and especially during heavy south-w«st weather; and the object tors, from this fact, arrive at the conclusion that sewage discharged at the proposed oatlet will come on to the beach in considerable quantities from the operation of the same causes that bring seaweed and floating matter on to the beach. It is clearly proved that large quantities of seaweed and floating matter come from a south-westerly direction! and the experiments conducted bv Mr Smaili (chairman of the Tomahawk Road Board) hi the presence of Mr Smith (as illustrated in Drainage Board exhibit A) show a current or back wash from a south and easterly direction, which seema to strike the iMand on the cast sfle a little south of a Bne drawn through its- centre, because floats and seaweed let loose from points A and 'B travelled north and west bevond Tomahawk Bluff, while floats from G~, D, and E went in an opposite direction' seawards.

The case for the Drainage Board is: a) That Bird Island is the most seaward point on that part of tlte coast, and is eiiiht chains beyond the line of adjacent headlands.' '(2) That the drainage will be discharged into deep water, the depth at low tide at the most southerly duct frpm the basin being from 18ft to 20ft. (3) Tha-/ sewage will bo discharged in an almost liquid form. (4) That an ocean current fipws along the coast in ajnortherly into-JBini

Island and then cut to sea. (5) That the discharge will be into this current, and if any escapes shorewards it will become so diluted by tie large body of water between the basin and the shore as to be harmless and not likely to reach the beaeh. The first proposition is beyond dispute, and the location of the proposed outfall is approved in the highest terms by Mr Rawson, engineer of the Orago Harbor Board, and by Mr Mason and by Mr Barr (civil ind Dr Kernot (consulting engineer) describes it as an "ideal ocean ontfiUL" The second and third propositions have not been disputed, and can be accepted as proved. As to the fourth proposition respecting the ocean current, the Admiralty chart shows a main current running up the coast in a northerly and easterly direction, corresponding with'the result of experiments made by Mr Anderson, but it cannot be ascertained from the chart how near the current ar> E roaches any portion of the coast or Bird sland. Mr Anderson's experimentfi, conducted from a steamer and boat on four days in July, 1902, go to show that the current at those timas came close in towards Bird Island, and was there deflected seawards. •Mr SmailTs experiments with flouts thrown from the island into the sea on January 26, 1905, at the points marked 0, D, and E in D.B. exhibit A, show a current then travelling in the same direction seawards. The important question of whether this current under all conditions of wind and weather approaches to Bird Island and thence flows seawards seems to me to be incapable of poof without long-continued experiment. I believe it to be common knowledge that it is an almost invariable rule that currents from time to time vary more ox less in direction, speed, and proximity to a coastal line. The fifth proposition is. that if any sewage escapes shore-wards it will be harmless, and not likely to reach the beach. The evidence shows that in heavy southwest weather the waves break with great force all over the south portion of the island, covering the proposed site for the basin and outlets, and the broken water flows shorewards on both sides of the island. The sewage at such times must necessarily mingle with tlie broken water flowing shorewards, and ecme portion of the contamination must reach the beach. This weald happen enly at or near 'high tide, when there would be a considerable body of water between the island and the beach, with which the drainage would mingle. To what extent the sewage will be likely to reach the hhore and accumulate on the beach and in the sand the witnesses very widely differ in opinion, and it seems to be a question impossible to be determined in any other way than by the actual discharge of sewage at the nroposed outlet and observation of the result. That is the opinion of the three consulting engineers expressed in the preliminary engineering reports at page 25 in dealing with a proposed outfall at Lawyer Head (.vide Marine Department file). Tho conclusion I come to, after full consideration of the evidence and the argument of counsel, is that the result of the discharge of sewage at Bird Island in the maimer proposed would be that same portion would reach the foreshore at Tomahawk BeachThat it is impossible to foresee the extent to "which the beach would become polluted, and the- principal danger would be from the effect of accumulation at high tides; but as sewage could only reach there in extremely diluted form, the evidence does not satisfy me that it would be sufficiently appreciable to create a public nuisance or cause danger to the public health, and thereby deteriorate the value of property in the neighborhood. The question, however, is so incapable of demonstration by less than actual experience after works have been constructed and used, that my opinion is that it would be inadvisable to authorise the discharge at Bad Isiand without provision being made that if it be found at any time that the sewage pollutes the shore to an appreciable and injurious extent, all tho sewage be treated in a septic tank, as was recommended by the three engineers in reference to the proposal to make the outlet at Lawyer Head (see page 25. preliminary engineers' report). This subject was referred to by counsel (see address of counsel, pages 35, 36, 39, and 40), and Mr Sim pointed out that, in the evtnt of it being possible for sewage to get on the beach in appreciable quantity, there was nothing to prevent the l>raiuage Board, without a great expenditure, from subjecting the sewage to bacteriological action before it reached the beach, and that it could be provided for without interfering otherwise with their present scheme. Enclosed with the exhibits is a copy of a resolution of the Tomahawk Road Board to the effet that the Board would withdraw opposition to the Drainage Board's proposal provided the sewage be subjected to sufficient septic action. This appear?, to me to present a favorable solution of the difficulty, but I think it is not advisable tint the Drainage Board should incur tixe cost of providing the necessary plant and works for septic treatment before it is demonstrated that they are required. With regard to a proposed outfall in the neighborhood of Trig 1), to the eastward of Tomahawk Point, this is strongly objected to on behalf of the Drainage Board, and their engineer (Mr Anderson) regards it as far inferior to Bird Island. In his opinion it would also cost- about £3OO per annum for pumping to a higher level, so as to have the outlet at a sufficient height and the sewer at a proper grade, and also about £5,000 more to construct. The evidence leads me to think that this is an overestimate in both respects. Mr Anderson also says (see page 25) that in K and N.E. weather there is a current inshore flowing westerly between Bird Island and the shore, and in his opinion there is more risk of sewage coming on to Tomahawk Beach from an outfall at the Tomahawk headland than if it- were at Bird Island. Mr Smaill, on the other hand, expresses a confident opinion that nothing travels westward round the point, and he is supported by other opinions to the like effect. No experiments to test this question have been conducted, but there is evidence that the sand spit between the islands and the shore is causwl by ijte meeting there of two, shore currents from opposite directions, and there is nothing to show that the current from the eastward docs not come round the point at tho;e times This view is supported by the course taken by the floats and seaweed" liberated at points A, B, and G (see D.B. exhibit A). Careful experiments would rerun re to be made in the neighborhood of Tomahawk Point extending over a reasonable period of time and under varying conditions of wind ard tides to determine whether sewage discharged at the proposed outfall near Trig U would be likely to reach Tomahawk Beach.—l have, etc.. E. H. Cabkw. Commissioner.