DRAINAGE BOARD.

Globe, Volume VIII, Issue 812, 29 January 1877, Page 2

DRAINAGE BOARD.

Monday, January 29. A special meeting of the Board was held in Mr 0. Clark’s auction rooms, at 11 a.m. to-day, to meet Mr Carruthers, and hear his evplanation of the complete plans for the drainage of Christchurch, Present—Messrs Tancred, (chairman), Hobbs, Jones, Wright, Harman, Duncan, Hall, and Ross. By leave of the Board, Messrs Manning and Jones, of the Heathcote Road Board, were in attendance. Mr Carruthers read the following paper:— "Christchurch, 29th January, 1871. "To the Chairman of the Christchurch Pistrict Drainage Board. " Sir—l have the honor to hand you a set of drawings, as enumerated below, showing a general scheme of sewers for the town of Christchurch and suburbs. The general plan shows the line, size, and direction of slow, of each sewer, and the longitudinal sections show the gradients. "I have divided the district into three parts - Ist, the high level district, the sewers of which are shown in blue lines ; 2nd, the northern district, shown in brown lines; 3rd, the southern district, shown in red lines. The sewage of the high level district falls by gravitation into the existing outfall sewer, and flows to the estuary. The sewage of the northern district is collected at the corner of Madras and Kilmore streets, there crosses the Avon by a syphon, and flows along the Kilmore street sewer to the East belt, where it is pumped into a high level sewer running along the East belt, and flows into the high level outfall sewer at Tuam street. "The sewage of the southern district is collected at the intersection of the South and East belts, and thence flows along a sewer to be built in the Ferry road to the Hargood road, where it will be pumped into a high level sewer in the last-named road, along which it will flow into the existing outfall drain. 11 The whole sewage of the (own and suburbs will thus be collected at the present outfall, and will flow into the estuary. “ It will be seen from'the sections, that notwithstanding the general flatness of the site of the town, the sewers will be placed at a considerable depth below the surface. It would cost an unreasonable sum to place them lower, and they are low enough for all practicable purposes. I have carefully avoided the pollution of the Avon, and with the exception of a few houses in Barbadoee street, the whole town will be drained to the estuary. The lower part of the Stan more road and the streets in Bingsland will also for the present be drained into the river at the Stanmore road. When it is found de sirable in the future to prevent this, a lowlying sewer can be built leading to the pumping station at Kilmore street. Th< amount of sewage which will be brought to t,he river by these drains will be very small, not a tenth part of what at present is 8.disposed of, and the cost of making the •above sewer would be too great in comparison with the small advantage to bo gained. “ Storm overflows are provided 'into the Avon at Montreal, Colombo, and Madras streets, and at Ward’s Brewery and into ihe Heathcote at the Hargood road. I cannot be denied that when these overflows are in use, the river will for a short tirn become slightly dirty ; but as the current in he Avon runs always in one direction, tbi will ba » very small nuisance, and is

at any rate quite unavoidable. The sewers are large enough to carry off a very considerable rsinfall, and it will only be during heavy rain, that even storm water will reach ifae Avon above Ward’s Brewery, “ The Heathcote is a much smaller river than the Avon, and ia influenced by the tide for some distance above the storm outfall, so th«t impure water will be carried above the outfall. When the latter is in use, b “mall dam raised to high wider level would prevent this, and would not be an expansive work, It should, I think, be constructed if any nuisance is found to arise by reason ol the storm overflow. *■ The sewers have been so arranged that in case of accident to the pumps no inconvenience would arise beyond the pollution by sewr.geof rbe Avon below Ward’s Brewery and of the Heathcote within the range of the tide for such time as the pumps were not at work. “The general system of construction proposed consists of sewers formed of brickwork on concrete invert blocks for the larger sizes, and of fireclay pipes for the smaller. AU junctions of sewers will be by tneans of man holes or lamp holes. Trapped gullies will convey the rain water to the man holes or sowers, and the houses will be connected by drain pipes direct to the sewer, should the system of house drainage be adopted by tho Board. It will not be necessary for some years to connect the houses directly with the sewers if the use of water closets is not permitted. The water supply from the artesian wells is so abundant that the concrete side channels which border the streets do not become very foul from the ordinary house slops, and no change is absolutely necessary from the plan cow in use of allowing house slops to flow into the side channels, and thence by the gullies into tho sewers'. Should, however, water closets he used this could not be allowed, and it would be necessary to have a drain to each house. I strongly recommend the Board to permit the use of water closets, I do uot go so far as to recommend their compulsory use at present, as I have little doubt they will, if allowed, very soon be generally used for the sake of their healthfillness, decency, and cleanliness. Breweries and other manufactories should however be compelled to connect direct with the sewers. “ As this is a very important subject, and one on which there is a great deal of misconception in the minds of the public, I will endeavor to give sufficient reasons for my recommendation that water closets should be used, and also that rain water be admitted into the sewers, as this point also has been strongly criticised. “ The primary object of sewers is not to carry water closet dejecta, but to remove household water after it has been used and fouled. It ia obviously a matter of the first importance to get rid of this filthy water, and underground sewers form the best vehicle for carrying it away. If it is allowed to fall into the natural water-courses they will be soon pllnted, especially where there are any manufactories in the town, and ordinary decency as well as wise economy dictate that this shall not be permitted. It therefore becomes necessary to dispose of the sewage in some other manner than throwing it into the rivers. I propose in the case of Christchurch to carry it to to the estuary, and I will presently state my reasons for doing so. “ Besides the removal of household water, the removal of rain water from the streets falls on the Board ; one set of sewers being in any case required for the household water it would seem to follow, without fear of eontradiction, that the simplest and cheapest way of providing for the rain water would be to mate the sewers large enough to carry it as well as the household water. By doubling the diameter of a sewer its carrying cayiacity is increased about six times, and this is more than sufficient to carry all but the heaviest storms. The extra cost of making the sewers large enough to carry ordinary rainfall is not generally very great, and in Christchurch or other flat towns it is scarcely appreciable, as the sewers have in any case to be made larger than would be sufficient, simply to carry a quantity of pure water equal in volume to the sewage, Tne size of a sewer ia regulated not only by tho quantity of sewage to be carried, but also by tbs necessity of obtaining a certain velocity of flow wh ch will prevent the deposit of silt. If the flow of sewage be insufficient, the solid matter held in suspension falls to the bottom, and there rests ; it then putrifies and spreads stench, discomfort, and illness. A town with a system of sewers which arc not self-cleansing, or capable of being cleansed by flushing, is in a worse case than a town without sewers at all. There are only two ways of getting this necessary velocity of flow, one by giving great inclination to the sewers, the other by mating them large. For instance, a 6in pipe would require an inclination of over 40ffc per mile to give the sewage passing through it such a velocity that the solid matters held in suspension would not sink to and rot on the boitom, and I need scarcely say that in Christchurch inclinations of 40ft per mile are not to be had. If the smaller sewers were laid with such inclinations it would be necessary to sink the primary ones far below the sea level into running quicksands. The cost of doing so would be beyond the means of .the Board, and even if money were forthcoming it would be sheer waste to use it for such a purpose. If Gin pipes were need, with a less inclination than 40£t -per mile, they would become simply elongated cesspits, and could not be cleansed by flashing, because the sewage, even when running full-bore, would not have sufficient velocfly to carry along to tho outfall the solid fetid matter suspended in the water j the solids would sink to the bottom, the sewer would become choked up with rotting matter, and after perhaps a few outbreaks of cholera or other deadly illness, would have to be dug up. Not being able to give ths necessary inclination, we must obtain flU'jKing power, by enlarging the sewers. As a practical matter, we cannot in Christchurch get a steeper inclination for the small sewers lhan 16ft per mile, and a lOin pipe is the smallest that can bo laid with so flat a slope, I have therefore adopted that; as the general size for small sewers. Iq a few cases, where a better inclination can be got, 9in pipes will be used, and for house drains where the full is great Gin pipes will be sufficient. “ A 9in or even a Sin pipe is larger than would be required to carry a volume of pure water equal to the sewage which will pass through the minor sewers, but it must be borne in mind that sewage is not pure water; it is water mixed with solid matter, and it ie just as essential that the solid matter be earned to the outfall as that the water itself be so carried, To reach this end we are obliged to use pipes quite large enough to carry ordinary rainfall, and this being the

case there is no good reason why they should not be used for that purpose. In the case of the large sewers the same course of reasoning applies. “ An 18in sewer would for instance be large enough to carry the sewage alone of the Ferry road system, but it would require a fall of 7ft per miie to keep an IBin sewer free from deposit, and such a fall would plunge tho outfall of the sewer 6ft below low water mark. The objections to such a plan are obvious, and the extra cost of: excavation in quick sand, together with the extra cost of pumping, would more than compensate for the economy in brick work in making the sewer smaller. “ In short, it may be staled that in Ohrirt* church or other towns where great inclinations cannot be given to the sewers, it is necessary to make the latter quite or nearly large enough to carry away ordinary rain, and the coat of a separate system of sewers for rainfall alone would be therefore an ua-.. necessary expense. \ _J “It is often urged that by keeping the rainfall separate from the sewage the lattermay be more easily utilised; but the value of the sewage is quite inconsiderable even when separated from the rainfall, and the loss arising from further dilution has been much overstated. Where a sewer has been made longer than just necessary, to carry the sewage, flushing must be resorted to; this is accomplished by’ darning back the sewage until the sewers are quite or nearly full, and then suddenly removing the obstruction. The sewage-thus acquires for a short time sufficient velocity to carry sediment along, and the latter by a series of flushes gradually carried to the outfall. I have arranged for admitting water for flushing purposes from the St Alban’s Creek, Jackson’s Creek, and the Avon into the principal sewers. Flushing can only be looked upon ss a palliative measure, and is far inferior to the thorough cleansing which is given by a heavy rain, when every sewer is running full bore and carrying all impurities away. It would surely be a very bad policy to forego the, benefit which thorough rain flushing gives, because it causes some small depreciation in the value of an article already nearly worthless. It would be sacrificing the whole good for the sake of which the sewers, were made, that is health and cleanliness, for the sake of a chance of saving a few pounds. “ Having thus disposed of the objections to allowing the rainfall into the sewer, I will turn to the very important question whether water-closets should be allowed to communicate with them. The first objection to doing so is that the sewage would be rendered more foul than is necessary. To someextent this is a valid objection, but ita urgency is generally overrated. The analysis of the sewage of various towns in Europe does not show any marked difference between the water-closeted towns and those with cesspits or tubs; the difference is not sufficient to enable a chemist to say with certainty from what class of town any sample of sewage had been brought. Waterclosets do not, therefore, in any perceptible degree add to the difficulty of disposing of the sewage at the outfall, and their advantages are so great that I have no hesitation whatever in recommending the Board to encourage their use by every means in their power short of legal compulsion. “In the manufacturing towns of England Lhere lo ono oorlous objection to the use of water-closets, which dooa not apply here, it is the loss of water which they cause. The water supply of those towns is generally insufficient to furnish the manufactories with the great quantity of 'water they require, and on this account the introduction of the water-closet sy-tem has been strenuously opposed, and every encouragement given to the inventors of tubs, carts, deodorisers, and all and every means of somewhat lessening the horrid nuisance attending the removal of nigh' soil. Most of these inventions are more or less effeciive when very carefully m naged. The houses of the rich have generally sufficient land attached to them to keep the privy at some distance from the house, and any failure of the n ght man to remove the tubs is at once made known to the proper authorities, and recurrence of the neglect prevented. Amongst the p-orer classes, however, these, systems have all failed; the closets are placed close to the dwellings ; the earth, or other deodoriser, is never properly applied; and the night man changes the tubs only when it pleases him to do so, knowing that complaint will not be made. *• The cost of maintaining carts and a staff of men is also very groat, and, even in the beat circumstances, the earth closet is far inferior in comfort, and decency to the watercloset, The value of the material derived from the earth closets is very small, and,, where the system has been adopted in England, it has been found impossible to find, purchasers for it, or even to get it taken,-: away for nothing. The usual method of. disposing of it is to purchase a piece of land,, on to which it is thrown, and where it becomes very offensive. In other cases it is* manufactured by a costly process into concentrated manure, and the cost of mamifacl- - is sometimes covered by the sale of themanure. The raw material has, however, no realisable value. “As above stated, I recommended the sewage of the town to be collected at the present outfall and allowed to flow into the estuary. I do not look upon this as the final manner of getting rid of it. There is no doubt that a nuisance will be created by sewage sludge being thrown by the tide on to the mudflats of the estuary, and that finally steps will have to be taken to wise dispose of it. Owing to the large yvater supply, the sewage will be mubTtr tainted,, and I do not think any great nuisance will be caused for twelve or fifteen years, and I do not therefore recommend the Board to incur any present expense in order to avoid it. Hereafter some process will he required, and it is possible that, in the meantime, somebetter onethanany nowinnse may be discovered ; if not the sludge may be thrown down by the line or A. 8.0, process, both of which are effective in removing solid matter from the sewage. The effluent water would then be sure enough to be discharg'd#' into the estuary without causing a nuisr.oce: Unfortunately, the manure obtained by these processes is cf very little value ; it m.igflt be carted with advantage on to tho neighboring ?Hnd hills, but no payment for it could be expected ; the process is alsoj, very costly. None of the precipitating processes hitherto discovered do more than remove from the sewage the solid matters suspended in it, and he effluent water is quite as valuable as a . manure as the original sewage j in most .-ases, indeed, it is more valuable, as the process consists of mixing with the sewage cer- ■ rin chemicals, the whole of which are uot ■ leqgvered in the precipitate.

“Irrigation baa been on the whole the most successful method of treating sewage. It requites a large original outlay for land, tor preparing the same, and for pumps and other machinery, but it may be made to return a part of the interest if not the whole, 1 think if land can be procured at a moderate cost, it would be well for the Board to acquire 300 or 400 acres; the latter area would be sufficient for the sewage of 60,000 people. The district between the outfall drain and the : sea is well suited for the purpose, being a very light sandy loam, varying to pure sand. It is of very little value at present, but with copious irrigation would produce good crops and give a sufficiently pure effluent water. I believe when th« town becomes more populous, and the sewage more concentrated than it is at present, that a sewage farm might be hero worked so as to pay interest on the outlay. Under the existing conditions of the town it could only bo worked at a heavy annual loss. " A third alternative plan of disposing of the sewage would be to carry it to the sea by means of an outfall sewer, about three miles long, into which the sewage would bo pumped. “ There is no immediate urgency for the Board to decide which of these plans it should adopt. If it were necessary to decide at once, I should recommend irrigation ; but I am sure no practical nuisance will be caused for many years by discharging the sewage into the estuary; “ As the sewage of two-thirds of the town will have to be pumped it would be very desirable that the Board should have power to prevent persons from allowing their artesian wells to run into the sewers or side channels. At present the, tho amount of sewage water is estimated by Mr Ball at about 250 gallons per head of the population nine-tenths of which is simply overflow from the wells, It would not be the least inconvenience to the citizens if each well were furnished with a tap, and tho water allowed to flow only when wanted, while it would greatly reduce the quantity of sewage to be pumped for which the citizens themselves will have to pay. “ While the sewage is so diluted as it is at present there would be very little ill results from allowing it to flow into the rivers for a short time; and I think it would be as well not to order pumping machinery until the works are nearly completed, and a better estimate can be formed of the quantity which will have to be lifted, than can be formed so long as it is uncertain whether the waste artesian water can be kept within reasonable limits by legal enactment, “ The drainage of the subsoil of towns is of great importance, but is often entirely neglected. When sewers were formed of porous material, put together in a slovenly way, they acted very effectually as subsoil drains ; unfortunately they let the sewage out as well as letting the spring water in, With sewers formed of good materials, and set in cement mortar, the spring water can only get into the sewers in comparatively email quantities, and special provision should d>e made for it. It has been found that on :ihe construction of drainage works the death ,tate from phthisia is greatly reduced, but that -the improvement often falls off after a year ■•or two, while the improvement in the death .rate from typhoid fever and other ‘ sewage • diseases’ continues to improve. This is probably due to the subsoil having been drained •and aerated during the construction of the ’works, and becoming afterwards water logged as it was before, ‘ ‘ I propose putting a common agricultural •drain pipe into each sewer trench before it is closed up, and giving it free communica■tion with the rivers. Also that a drain pipe is placed in all the existing drains and ichannels in the town before they are closed. *‘ I have not yet had time to prepare an estimate of the cost of the works, nor to design several of the details, such as overflows and special flushing arrangements, but the accompanying plans are sufficient to enable the Board to proceed -with the construction of the main body of the works. “ I enclose a set of conditions of contract: and a specification of the manner of constructing the works of the Ferry road sewer, ■which will serve generally as a specification ■of the other sewers. “I recommend the Board to purchase themselves all the pipes and cement which may be required, and I am sure they would carry out the works better and cheaper under the direction of their own officers than by the aid of contractors. Mr Bell has got quotations from the makers of pipes in the colony and from Home makers, from which it appears that pipes can be imported cheaper from England than they can be made hero. The quality and finish of the English pipes is also better, and I think the Board should order all they require through an agent at Home. At the same time, the more complicated parts of sewer work, such as invert b 'ocks, gullies, &c, could be imported. If h ouse drains are to be allowed, the whole woi’k of laying them and connecting them with the Binks and cloßets should be done under the supervision of the Board’s inspectors, atf .they will otherwise be sure to be carelessly doF'e. . ti 2’Jjq sewering the town iSj ox cours6j the most urgent ot' the works of the Board, and that to which 1 have given most attention. The surface drainage of the outlying districts has not, how ever, been overlooked, and will be specially reported on hereafter, , . »I have the honor to be, sir, “ Your most obedient servant, “ JOHN OABEUTHEBB, M.1.0.E, After a lengthed examination of the plans by the Board, Mr Duncan moved— “ That the Board begs to tender its thanks to Mr Carruthera for his clear and lucid explanation of the drainage scheme prepared by him.” Mr Hobbs seconded the motion, which was agreed to. Mr Wright moved the adoption of the plans submitted by Mr Carruthera. There was evidence before them that the scheme had been thoroughly worked out, and he was ■are the result would be satisfactory to the public. Therefore he had much pleasure in moving the adoption of the plans. Mr Boss had great pleasure in seconding the motion. The Board did not slavishly bind themselves to the plans in every little detail, which it might seem advisable to alter, Mr Wright remarked that by this scheme the sewage could be pumped from the extremity of the outfall drain to the ocean. The public ought to know that this could be done at a cost of from £50,000 to £IOO,OOO additional. The motion was agreed to. The Board then adjourned until Monday -next.