THE CITY DRAINAGE SCHEME.

New Zealand Times, Volume XXXII, Issue 5193, 13 November 1877, Page 2

THE CITY DRAINAGE SCHEME.

MEETING OF THE COMMITTEE. An adjourned meeting of the Drainage Committee, which consists of the whole of the City Council, was held yesterday afternoon £o consider the drainage scheme. Present —His Worship the Mayor, and Councillors Greenfield, Allen, Hunter, Allan, Moss, Macdonald, Dixon, Fisher, Logan, and Maginity. It will be remembered that at the former meeting a, report from Mr. Napier Bell, the consulting engineer, was read, which was unfavorable to Mr. Cliraie’a scheme, and the latter gentleman then applied for a week’s time to prepare a report in reply. The application was granted, and the following report from Mr. Olimie was now laid before the Committee : “ Gentlemen, —I beg to submit for your consideration my answer to the report of Mr. 0. Napier Bell, on my scheme for the drainage of the city. “ I desire to remark at the outset that it is evident from the tenor of Mr. Bell’s report, although he has not so expressed himself in plain terms, that he lias had in his mind the belief that the outlet for the sewage should be the bay. Holding this view, it would appear that ho has, not regarding some other outlet as a necessity, magnified the drawbacks to my scheme which presented themselves to him, rather than sought to learn whether such objections were well-founded and insurmountable. He appears to have lost sight of the primary condition laid down by the committee; that the sewage should not be discharged into the bay, and the Government would not permit it to be emptied into the harbor. “ As there are now several new members on the 1 committee, I trust it will not be considered out of place to refer to the terms agreed upon at the time I undertook to furnish a report. When asked by the committee to do so I replied that I should prefer competing with other engineers, for the reason that I did not think it would be just to myself to propound a scheme, and that after publicity had been given to it other engineers should have the privilege of giving a report. The committee assur. d me that if they approved of the scheme I might lay before them, no other engineer would be asked to report. On this understanding I undertook the task, and completed it in a manner which I have reason to believe has met with general approval. When a consulting engineer was spoken off I at once said I had no objection, I of course considering that any engineer who might be appointed would be a gentleman of independent standing and of experience in this particular branch of engineering science. After carefully reviewing Mr. Bell’s criticisms, I am forced to the conclusion, which I feel reluctant to declare, that he has not given such care to the investigation of the scheme submitted to him as I could have wished. “ To show that I am warranted in holding this view, I will refer in the first place to the objections to the pumps. He speaks of accidents that might happen to them, and assumes that in such an event they could get no relief, saying there can be no overflow from the pumps to Taranaki-street, on account of the depth of the main sewer, from that part of the town south of Majoribank-street and Dixon-street, an area equal to about twothirds of the whole city. “ I am glad to be able to assure the committee that no such cause for alarm exists, therefore such an objection should never have been advanced. Mr. Bell would appear not to have perceived that the whole of the sewage from this large area could at once he turned into the bay should anything happen to the pumping machinery ; and he lias been guilty of this oversight notwithstanding that he was provided with sections of every street in the city, showing the height above the level of the bay. I should here observe that I mentioned iu my

report that an overflow would be provided in order to meet any such contingency as the stoppage of the pumps, and I would not have done this unless I had proved that it was practicable. Thus in the event of anything happening to prevent the discharge of the sewage through the tunnel to the sea an efficient overflow would be provided for its escape, and neither injury nor nuisance would arise to any part of the city in consequence of a temporary stoppage of the pumping machinery. To make this clear I submit a diagram, showing the way in which I propose to dispose of the sewage in case of an accident, and how this overflow may be made available in a few minutes. “ One objection, which, as put by Mr. Bell, would strike a careless reader of his report as very serious, is utterly fallacious. It is based on an error of such a nature that I am surprised that any consulting engineer could have fallen into it. He refers to the sewage being dammed up to stagnate in the tunnel in consequence of the valves or buckets of the pumps being choked by articles getting into the sewers ; and old hats and trousers are referred to as things that might cause such a state of affairs. This surely is convincing proof that Mr. Bell had but an imperfect knowledge of what he was -writing about, otherwise he would not have prognosticated an evil which could not possibly occur, for the simple reason that the pump I recommended in my report has neither valves nor buckets ; therefore, what does not exist could not get choked. My report refers to Bastier’s chain-pump, and I particularly mentioned that one great merit it possessed was its freedom from liability to get choked by sewage. I venture to assert that no such piece of mechanism was ever constructed to lift water or sewage as a chain-pump with valves and buckets. A chain-pipe consists of a rectangular case through which an endless chain works, having at intervals a rectangular plate of wood or other material so arranged as to be horizontal as it passes up through the case. Should a screen be required there is no reason, as far as I am aware, why it should be placed at the bottom of a shaft 57ft, below the surface, as by placing it ®t the north end of the tunnel it would be at a much less depth. “ In referring to the proportion of the rainfall which will be admitted into the sewers, Mr. Bell speaks of it as exceeding the pumping power. I cannot understand how he could have supposed such an erroneous idea. It is plainly stated in my report, and I also spoke to him of this when he was here, that the amount of rainfall that would be allowed to enter the sewers would be three-tenths of an inch vertical over an area of 1000 acres in twenty-four hours. That, added to five cubic feet per head for a population of 50,000, would produce during a period of twenty-four hours 1.339.000 cubic feet, which would be the maximum quantity, and the engine and pump would be af sufficient power and capacity to lift to the height required in twenty-four hours 1.140.000 cubic feet. I even went so far as to show Mr. Bell my calculations by which these totals were arrived at. I may here observe that the rainfall allowed to enter the London sewerage works is one-eighth of an inch vertical for the urban district, and a quarter of an inch vertical for the suburban district, during twenty-four hours. This system, known as the “ Separate System,” is now universally l recommended, whether the sewage requires to 1 be pumped or not. Consequently I am at a loss to conceive how Mr. Bell could advance such an unheard of contingency as being likely to happen in this particular case. With respect to the subsoil water, it Svill suffice to remark that all sewers and drains would he so constructed as to prevent leakage of sewage from within, and they would, of course, be impervious to the subsoil water from without. “ Mr. Bell’s next supposition referring .to the pumping is the inconvenience he says would arise from the engine working only twelve hours per day. Why he should fix on twelve hours as the maximum daily time for the engine to work I cannot tell, as I distinctly informed him, when showing him my calculations, of the time I intended the engine to work; and although I have had a large experience among engines of various descriptions for many years, I certainly never before heard of an engine being limited to either twelve or twenty hours per day if there were twentyfour hours' work for it to do ; and further, to show that I never intended the engine to work only twelve hours daily, I mentioned in my report that in England engines of the type I had recommended had ue .n working night and day over twenty years without requiring any material repair. Mr. Bell himself complains of the great evils that would arise from the pumps being worked for only twelve hours daily; hence his limiting them to that time is a mystery, particularly as there can he no reason adduced for so doing. The apprehension that the sewage would stagnate in the tunnel and be forced back into the sewers and thence into the streets, is undoubtedly the main feature in his opposition to my scheme ; and if this difficulty, which has been such a stumbling-block to him, could not have been provided against, I should not have recommended my scheme for adoption by the committee. T hope, however, I have clearly shown that I have made sufficient provision to avert such a disaster. “It is I think unfortunate that Mr. Bell did not spend a little more time with me when he was in Wellington, as by doing so he would have given me an opportunity of pointing out and explaining to him this aud oth r proposed arrangements which he does not appear to have grasped. He commences his report by saying the principal feature of this project is the main intercepting sewer, and in this he is quite right, as on this sewer will depend the successful drainage of the city; and it certainly may be regarded as gratifying that in this the most important part of the scheme he has apparently failed to find any material fault either iu the varying rates of inclination along its course, the size of the shafts for ventilation and their number, or the sectional area of any of the culverts. “The report comments on the size of the pipes proposed by me, aud endeavors to show that they are capable of draining larger areas than those they are intended to drain. “ It begins with the Tinakori-road pipe of 12iu., and strives to make it appear that, though it is intended to drain 42 acres, it is capable of draining 200, its capacity being five times greater than necessary. The sectional area of a one-foot pipe is '7854, the one-fifth being T5Bl, or less than a pipe of six inches in diameter. I may say that the only pipes the size of which was spoken of by Mr. Bell to me, were those on the Tiuakori-road, and he said ; —“ The pipes in this particular street ought to be large to carry the water to the main sewer, so that sufficient may come down iu force from the reservoir to clear away all accumulations.” I told him I would put down a nine-inch pipe from the reservoir intended to be constructed, and he did not appear to think this too large. It will require Mr. Bell to show how the water from a pipe Sin. in diameter running with a full head, is to pass through a pipe on the same gradient of less than 6in. diameter, which has a sectional area less than one-half of a Sin. pipe. He refers to the extravagant size of the pipes proposed by me for several of the streets ; but I am quite prepared to give satisfactory reasons for all the different dimensions I have recommended. However, to do so would increase very considerably the length of this report, aud as I desire to avoid that, I will only refer to one or two instances. Doubtless some slight modifications may be made during the progress of the works, in this as in all other large undertakings ; indeed, it would be a very unusual thing if a work of this magnitude were devised so that no detail, here and there, could be improved upon ; but surely a slight difference of an inch or two in the diameter of a pipe-drain cannot be considered as having anything to do with the practicability or otherwise of the scheme ; besides, the exact size of sewers or pipes in certain situations is only a matter of opinion, there being no dogmatical rule to he adhered to. The 18iuch pipe in Ingestre-street is objected to for the reason that, although it is intended to drain 100 acres, it is capable of draining 800 acres. The fact is this pipe is net only intended to drain 100 acres, but it will have to carry off the drainage from the sewers to the south of it as well as water from Polhill Gully for flushing the main and other sewers. “ Kef erring to the 24-iuch sewer in Vivian-

street, Mr. Bell raises the objection that it could discharge one and three-quarter times as much as the outfall sewer at Pirie-street, to which all the sewers of the town are tributaries. Further on the report says :—‘From these cases which I have investigated, I come to the conclusion that all the pipes, except the smallest, are too large for the purpose.’ He may therefore be said to have condemned all the pipes except the smallest. Now, thesmallest pipe I recommended was four inches. The gradient upon which the 4-in. pipes will be laid will vary from 1 in 20 to 1 in 50. I will take the average as 1 in 36, although it would be considerably under this. As he has evidently taken the theoretical discharge of pipes according to the ordinary formulas, it isbut fair that I should adopt the same course. A 4-in. pipe on a gradient of 1 in 36 would discharge over 25 cubic feet per minute (I will not trouble the committee with decimals). I have recommended that each house be-pro-vided with a 4-in. pipe drain. The water supplied to each person per day is ;s0 gallons, or say five cubic feet. With five persons to each house, the discharge of sewage per house per day would he 25 cubic feet. Taking the rainfall from the roofs, &c., at 100 (one hundred) cubic feet additional, would give 125 (one hundred and twenty-five) cubic feet per house per day. But a 4-in. pipe on a gradientof 1 iu 36 would discharge 25 cubic feet per minute, being 1500 (one thousand five hundred) cubic feet per hour, or 36,u00 (thirty-site thousand) cubic feet per day. Yet the daily duty of this pipe would be only 125 cubic feet. Thus so far as the theoretical capacity of the pipe is concerned, it is large enough to drain 288 houses. “ With reference to the remark that the two-feet pipe in Vivian-street could discharge one aud three-quarters as much as the outfall sesver at Pirie-street, I wish to point out this : With a population of 50,000, the discharge at the outfall sewer would he 1,399,000 cubic feet. One and three-quarters equals 2,343,250 cubic feet per day of 24 hours. Then by the same rule as that adopted by Mr. Bell, a fourinch pipe on a gradient of 1 in 36 can discharge--36.000 cubic feet per day. 50,000 people, at five to a house, gives 10,000 houses. Then 36.000 x 10,000 = 360,000,000 cubic feetper day, being 250 times greater than the capacity of the outfall sewer at Pirie-street. “ Some of the pipes are condemned by Mr. Bell because they are capable of draining an area only five times greater than the district allotted to them. Yet he has actually approved of the size of pipes (four inches) capable of draining 288 times the area allotted to them. I make no comment upon thja further than to say that, theoretically, less than ‘ a half-inch pipe ’ would suffice for each house, but who would think of laying one down ? “ Mr. Bell remarks on the expense of having two sets of street sewers, one for the sewage* and the other for the storm-water, hut the latter -would not be required in Wellington owing to the number of water-courses which cross the streets at different points, and the surface channels would be capable of conveying all the storm-water. I know of no streets in Wellington that would get flooded if provided with proper channels. “ The report speaks of the sewage of the city as insignificant at present, and apparently not very formidable in quantity should the population increase to 50,000. However, I fear a very short time would elapse if 250,000 cubic feet or over 7000 tons of sewage were discharged daily—well, I will say into the bay,, before the significance of such-a course would make itself felt. “ Mr. Bell considers that two engines should be provided. I say undoubtedly so, and for this I have estimated, but certainly not two of the size proposed by him, as I intend .the engines to work twenty-four hours, .when necescessary, aud not to limit them to twelve hours daily as he does. I have estimated for two engines of about thirty horse-power each, and one of these would do all the work with the present population. “ Mr. Bell expresses the opinion that he would expect to find the pressure of water along the course of the proposed tunnel to be enormous. He states that in many English towns the -water to be contended with in tunnels amounts to one-half, and even to twothirds of the quantity of the sewage. I am pretty' well acquainted with many of the tunnels in England and Wales, and I certainly never heard of such a proportion being met with, or anything approaching to it. A short time since I had some particulars of the tunnel now being made under the Severn near Bristol, and there does not appear to be one-third of the quantity of the water referred to by Mr. Bell to contend with, notwithstanding that thetunnel is carried under the bed of the river. He alludes to the line of tunnel as “ situated in the centre of a deep valley with high mountains on each side.” X think it will be apparent to any one who knows the locality that this is incorrect. The tunnel will pass under a ridge which divides the Te Aro district from the valley leading to Island Bay. X quite agree that considerable savings in first costand working expenses -would be effected by erectiug the pumping station at the north end or inlet of the tunnel, and this I pointed out in my report. The committee, no doubt, will recollect that they positively decided against such an arrangement. “The report refers to the outfall sewer asbeing larger than necessary for the discharge of the sewage and rainfall. Theoretically this is correct, but if it be a fault, I think it is on the right side. The cost will be but little more than that of a tunnel one-third smaller, and should the population of the city increase beyond 50,000, the larger size would decidedly be preferable. Besides, in designing sewers, it is usual to reckon the general maximum flow at about two-thirds full, and the size I have designed the outfall sewer accords with this principle. Mr. Bell appears to calculate on the sewer running full. My report referred to, aud provision was made in my estimates for an underground reservoir near the pumping station, and I told Mr. Bell that this was to be formed by enlarging a part of the tunnel to a sufficient size to hold some hours sewage during dry weather; yet he puts this forward as a suggestion of his own. “ Mr. Bell writes, ‘ I think I have advanced sufficient reasons against the practicability of the scheme,’ &c. He has certainly advanced many supposititious objections, but I fail to see iu his report any one defensible reason against the practicability of the scheme. The only serious objection—could it have been sustained—was. the damming back of the sewage. If Mr. Bell had given this part of the project the consideration I should have expected any professional engineer to bestow, he would, I imagine, have discovered that means could be readily devised to avert such a calamity; I cannot but express surprise that an engineer provided with sections of every street in the city, showing the heights above high-water mark, should fail to see a remedy for such an evil; and I think the committee will hold this view when they examine the plans and drawings I shall have the honor to place before them. “ The estimate of cost appended to the report is certainly greatly in excess of mine, notwithstanding that he considers the size of the tunnel may be much lessened, that the pipe-drains may be also materially reduced in size ; and notwithstanding that Sir. Bell says the pipes could be imported at a cost of 20 to 30 per cent, less than they could be supplied in the colony. Yet with these reductions his estimate is about half as much more than mine, clearly showing a great discrepancy somewhere. But in support of the reliability of my estimate, I have strong evidence of two kinds—oue is the value for the whole of the works, as calculated by several substantial and experienced contractors ; the other is the fact that contracts for all sewers aud drains recently let in Wellington have been taken at rates considerably below the prices upon which my estimate was based. ■ Without calculating on the low price of the imported pipes referred to, I am confident that all the works comprised in my scheme can be efficiently carried out within my estimate. I am glad Mr. Bell admits having only guessed at the cost of the tunnel, as his estimate is far above mine aud that of several contractors. “I observe he complains in many places that the plans are not sufliciently finished. 11 is, I think, to be regretted that he did not mention this to me and say what other plans

lie required. For uiy own part, ; I_ contend, tbafc the plans were sufficiently finished, and were as many as necessary to enable any engineer to report most fully as to the practicability or otherwise of the scheme. X have myself acted as consulting engineer, and for many years X had a good deal to do with gentlemen acting in that capacity ; and I unhesitatingly affirm that I never knew one supplied with plans, sections, and other information so fully as Mr. Bell was. It_ does to me seem strange, to say the least of it, that I should not have heard a word of such a want until I read it in his report. Mr. Bell suggests that reservoirs should be constructed at the upper parts of the principal creeks for flushing the sewers. It will be remembered that is a part of my own scheme, and I discussed it with him. Mr, Bell says he had no levels of the streams to enable him to judge ef the heights. Certainly he was not supplied with sections from levels taken along the beds of the watercourses, simply because they were not needed ; but he was supplied with sections of the streets along the sides of the streams intended to be utilised for flushing, and as these streams practically follow the same gradients as the streets, no one at all acquainted with sections could have any difficulty whatever in ascertaining the heights of the watercourses, the altitude of the different points above the bay being shown in plain figures. I very much regret that I should have been compelled to criticise so severely the report of the consulting engineer, but from the character of Mr, Bell’s review of my scheme, it was impossible for me to do other than expose his fallacies in clear and unmistakeablo language. It should be borne in mind that my scheme was the outcome of much patient thought and scientific investigation. It was no hurried and rash conclusion, unsupported by detailed plans and estimate. I must say I regard it as very unfortunate that Mi. Bell, when in Wellington, did not spend a little more time with me in consultation, for I atn sure had he done so many of the objections would not have appeared in his report. I will only add, in conclusion, that it has been my endeavor, while avoiding technicalities, to lay before the committee ns succinctly as I possibly could a refutation of the various allegations advanced against my scheme for the sewerage of the city. “ Should there be any objections which the committee think I have not sufficiently answered, I shall he happy to go further into the subject to prove that I can substantiate all I have advanced as to the practicability of the works and their cost.— I have, &c., “ Daniel Cliiiie, “ Wellington, 12th November, 1877.” The Councillors were each supplied with a printed copy of the report, which they severally read over, an operation which occupied about a quarter of an hour. The Match said the report was now before the committee for them to deal with. Had any member a resolution to propose ? Councillor Hosier said he would be a bold man who would propose a resolution upon a report just laid before them without having had time to deliberate upon it. He for one felt himself quite unable to offer an opinion ou the subject at present, and he would support an adjournment to a future day. The Mayor said every member of the committee must feel the force of the remark. He regretted that the report of Mr. Climie had not been laid before them sooner. , Councillor Looak said he heard that Mr Clarke, an engineer who had been sent for from England by the Sydney Government, was likely to visit Christchurch, and suggested that he should be consulted. In reply to the Mayor, Councillor Logan said he understood Mr. Clarke was specially versed in this particular branch of engineering science, and had been brought out by the Sydney Government on that account. Councillor Maginity said before going any further he thought it would he well to settle the question as between Mr. Bell and Mr. Climie. Councillor Hdnter said he had never understood that the Government had positively refused to allow the drainage to be carried into the harbor. That, he believed, depended very much upon there being a proper reclamation, at the Te Aro end of the town. Coun cillor Greenfield supported Mr. Clarke being consulted in the matter. Councillor Maginity thought that the drainage might be carried into the harbor, and a system of earth closets might also be established. Councillor Fisher supported the carrying the drainage into the harbor. Councillor Hdnter said he entertained much the same view. With regard to Mr. Climie’s scheme, estimated to coat £BO,OOO, he should not be surprised if it cost £300,000, and even then its success might be doubtful. He referred to the sickness caused in. Sydney by the accoumulation of noxious gas in the pipes, caused by their being choked up. Councillor I'IXON thought the sense of the Council should be taken on the desirability of establishing an earth-closet system, having the njf'htsoil carted away, and the drainage be carried into the harbor. Councillor Allan said he thought the opportunity should be given to Mr, Climie to devise an alternative scheme. Hitherto he had been limited to carrying out the drainage system here by other means than draining into the harbor. Councillor Hdnter deprecated any hasty action being taken in the matter, and suggested that the two schemes should be submitted to Mr. Clarke. They had before them the opinions of two professional men which widely differed from each other. The Mayor said if it were decided to adopt a system of drainage into the harbor it would be unnecessary to, go on with Mr. Climie s scheme ; but at this meeting he did not think it desirable to bring forward a motion of such magnitude. Mr. Climie said that at Brighton (England) the system of draining into the sea had been tried, but had been found to be a nuisance, and had to be abandoned. The nuisance was caused by the gases being driven back by the rise and fall of the tide. Councillor Hdnter said by the drains being kept flushed with salt water this could be Councillor Looan moved, and Councillor MaCINITY seconded, —That the Mayor be requested to place himself in communication with Mr. Clarke, of Sydney, as to whether that gentleman will give the Council the benefit of his advice respecting the drainage of the city of Wellington. This was seconded, put, and earned. A letter was read from the secretary to the Premier, stating that Sir George Grey would be happy to meet a deputation of the Council to consider the question of introducing the Contagious Diseases Act into Wellington. The°Council resolved to wait upon the Premier at eleven o’clock on Wednesday morning next. The Council then adjourned.