DRAINANE OF CHRISTCHURCH AND SUBURBS,

Globe, Volume IX, Issue 1260, 2 April 1878, Page 3

DRAINANE OF CHRISTCHURCH AND SUBURBS,

ME- CLARK’S EE POETTO THE CHAIRMAN AND 'MEMBERS OF THE DISTRICT DRAINAGE BOARD, CHRISTCHUECH: Gentlemen, —Having been honored with your instructions to inquire into the circumstances and conditions which have reference to improving the drainage of the city and its «üburbs, I have carefully considered the subject, and now beg to submit my report. 1. Christchurch is situated on an extensive plain, which has been formed by material washed down from the mountains under the influence of the weather, acting through long periods of time. Above the°jcity, the plain rises towards the mountains at a slope of about 20ft. per mile ; while below and towards the sea, from which the city is distant five miles, the inclination is at the rate of Sift, per mile. Thus at a distance of nine miles above Christchurch the water level in the Waimakariri is at an elevation of 145 ft, above the city, the river bed is strewn with boulders and pebbles which travel down stream in times of flood, and have thus been spread over the plains. At the point above-mentioned, and below towards the sea, the river has no proper banks, and the constant vigilance of the Board of Conservators is required to keep it within its channel; on one occasion its waters escaped, and a portion passed through Christchurch on its way to the sea; to prevent the recurrence of this, the Board of Conservators was established, and the protective works' they have carried opt to yeeieb the current in the yiyey

General returns for 1877 not yet published. Mortality of Christchurch, as gathered from monthly returns, under 17 per 1,000._ cumulative process, the number of inhabitants is at present very small for the area occupied, and the usual results of long occupation on an undrained site have not been developed, therefore the necessity for remedial operations is not so evident as in older cities ; and it is a question with many persons whether any measures are now necessary to prevent, anticipated evil; and among those who do recognise the necessity, there is a great diversity of opinions as to what the measures should be.

10. I would therefore point out what is to me the most prominent feature in its condition, as affecting the public health of Christchurch and its suburbs. This is its waterlogged site. Over a large area of the city, especially in winter, water is met with at from 4ft. to a few inches only below the surface of the ground, and at Waltham the water during winter time is stagnant on the surface; while, therefore, the present imperfect removal of filth is a growing evil, the exhalation from a very damp soil is abundantly present, and the combination of these causes of mischief is really a present question, and one of degree, rather than one which may be deferred for future consideration with safety to the present population. Whatever maybe the divergence of opinion as to the actual causes which give birth to the various forms of zymotic diseases, there is a general unanimity as to their greater development under the influence of an impure and moist atmosphere, 11. Under these considerations, it appears to me indispensable that the measures to he adopted should not only comprise the removal of filth and surface water, but should, as far as it is possible, aim at lowering the level of saturation of the subsoil beneath the city, and insure a greater depth of dry soil over its entire surface.

12. And here I would remark, that the operation in which the City Council is engaged of making impervious footpaths and surface channels is entirely in the right direction, as it will diminish the amount of soakage into the soil, which occurs when the rain and surplus artesian water with its load

of sewage is made to flow through leaky channels, and will, I have no doubt, assist in promoting the public health, as well as the comfort of pedestrians. 13. In the course of my inquiries I have been provided with every information as to the measures which have been proposed to improve the sanitary condition of the city ; these, with the exception of a few suggestions from various persons who have interested themselves in the subject, are confined to the two schemes prepared by J. Carruthers, Esq., C.E., the first of which was a pumping scheme, with two pumping stations ; the second, a gravitation scheme. By both of these it was proposed to remove the rain water to the extent of iin. of rain in twenty-four hours from the entire area drained, with the artesian supply, by pumping it into the existing outfall sewer, and as a temporary arrangement discharging it into the Sumner estuary. This estuary is very shallow, and for the most part dry at low water; subsequently, in order to avoid the necessity for pumping, he revised the scheme, and proposed to effect its removal to the same place on the estuary as a permanent arrangement, by constructing a very expensive outfall sewer with a fall of I'4 feet per mile, and at a cost of £57,000. lam quite aware that these proposals have been strongly opposed; in the discussions on the subject which I. have read, there appears to be no other scheme which has passed the stage of mere suggestion They include: one, to continue the river as the receptacle for the fluid filth of the city —the night-soil being excluded; another, the cutting of a ship canal for the same purpose; and a third recognises the necessity for covered sewers, but at gradients so small as would inevitably make them sewers of deposit; while all the schemes recognise the necessity for the filth to flow through the street gutters for greater or less distances; and moreover it must be noted, that in every case the filth is by some channel or other removed to the estuary. Had more searching enquiry been made into these proposals, had the quantities to be dealt with and the cost of the work been estimated, it would then have been ascertained how very imperfect are the results obtained in proportion to the expenditure. 14. Surface drains have their advocates, because they can be easily cleaned ; but the necessity for this cleaning not only involves labor, but it recognises also a filthy condition requiring it. Surface drains are seldom watertight, and when they are not, they assist in keeping the soil in their vicinity saturated with the urine and house slops which they are intended to convey. However well constructed, surface drains facilitate the evaporation of filthy matter, and the consequent pollution of the atmosphere. 15. The night soil it is proposed to deal with by hand, as at present; but no greater mistake can be made than to suppose that the omission of this would leave the slops (which include a large portion of urine) sufficiently pure to render their presence anywhere near the abodes of man unobjectionable, either in the street side channels or in the estuary. All this has been very well pointed out by Mr Carruthers.

16. Undoubtedly, one of the most important points in connection with the subject is the character and position of the outfall. It may generally be stated that the flow of sewage matters should be constant, they should not cease to move from the moment of their production to that of their discharge beyond the limits of the drainage area. If these conditions be observed, there is no time for decomposition to take place, and the generation of gases within the sewers is prevented. The outfall being thus constant, it should also be such as to allow sufficient inclination within the system of sewers to secure a certain velocity of flow, and the perfect discharge of all matters admitted thereto —to prevent deposit within the sewers. The inclination may be, as a minimum, 1 in 100 in house drains, and from 14ft. in the smaller sewers to 3|ft. per mile in the sewer which conveys the entire discharge of the city. 17" The natural drainage outlets from the area may be considered to be the Rivers Avon and Heatheote, the Estuary, and the sea. The Avon lias a course of seven and a half miles through the area ; it is naturally a very pure and clean stream, and except where the drains fall into it, the pollution is not at present apparent. It is, however, to be borne in mind that the population of thirteen per acre in the town area will probably increase to more than three times this number, as is the case with other cities ; while it is also probable that the present abundant supply from the artesian source will not greatly increase, as it is sufficient for the wants of three times the present population. When this time comes, I think there will he few who would advocate the discharge of house slops into the river, as it would be the conversion of the most beautiful feature of the city into a foul stream. Moreover, the surface level of the water is not sufficiently below that of the city to afford a sufficient fall in the sewers. I am of opinion that the use of this river even partially as the main sewer of the city, should on no account be entertained. The same may be said of the Heatheote, which could only be made available for a comparatively small part of the area. The tide also flows up this river to a point near to the city. This would check the flow, and render it undesirable as an outfall for the sewage. The same objection exists as in the case of the Avon ; the surface level of the river does not afford sufficient fall for the removal of the drainage. 18. With reference to the Estuary as a permanent outfall, experience has proved that the admixture of sewage with salt water is even more objectionable than with fresh water, and this, whether the sewage impurity be of animal or vegetable origin. In all cases when near to a populous district, it is undesirable to make permanent arrangements for the discharge of sewage into salt water, if it can in any way be avoided. When it has been done, nuisance has followed, and large works have been executed in order to avoid it, Brighton, in England, is a notable case of this kind. Where, as is the case with the Estuary, it is for the most part dry at low water, the sewage discharge is even more objectionable than into the sea, as a portion is left to evaporate on the surface when uncovered by the water. 19. This may be avoided in the manner suggested by Mr Bell, viz. :-~The provision of a tank to receive the sewage for six hours, and to discharge it at ebb tide. This would partially remove the difficulty, and the liability to pollute the Estuary, as the sewage would under these circumstances be discharged into the sea. But it would involve a stoppage of the flow for six hours, and, except as a temporary arrangement, I am not of opinion that the sewage should be discharged into the Estuary. Mr Carruthers’ proposal was to use the present outfall sewer, into which he\ intended to pump the sewage, and the land adjacent to the outfall not being at present occupied by buildings, would for a time admit of such temporary use until a more perfect arrangement is completed. 20. The permanent use of the Estuary as proposed by Mr Carruthers in his gravitation scheme, which also involves the construction of an expensive outlet sewer, with insufficient fall to keep clean without hand labor, appears to me to be an undesirable arrangement. 21. The remaining natural outfall to consider is the sea. This is even more distant than the estuary, the latter being three miles, while the sea is four and a half miles, involving the crossing of the Avon where it is wide. An expensive work of iron pipes would be necessary to discharge the sewage so far beyond the breakers as to prevent its being thrown ashore. There is, moreover, no advantage to be obtained in the shape of extra fall, and it would still be necessary to lift the sewage in order to its effective discharge into the sea, and to a'higher level than would be required to discharge it into the Estuary. 22. Rejecting the sea as an outfall, the only remaining possible disposal of the sewage is found in the suggestion to pump it on to land, and use it for the purpose of irrigation, and 460 acres of sandhills have been reserved for the purpose. These hills ’ are situated at a moderate distance of one mile and three quarters from the position in which I should propose to fix the pumping station, and are well suited to absorb large quantities of the sewage —proper drains being laid to the nearest point of the Estuary, where the filtered sewage can pass away. Apart from the expense of the puqiping operations, such an outfall possesses the a.dyftEt»|p of Wy possible

difficulty, and holds out some prospect of remuneration for the expenditure in the future.

28. My proposal is, therefore, to pump the sewage to the sandhills, and it remains to be considered what should be included in this proposal, in order to limit the first cost and working expenses for the scheme intended to improve the drainage and sanitary condition of Christchurch.

24. The following are the uses to which sewage works are usually applied:—The removal of the surface or rain water; the removal of the water supply after having performed its various uses for domestic and manufacturing purposes ; the removal of the excreta of the population, and the subsoil water. All these may bo accomplished by a well-designed and properly constructed system of sewers. 25. The first of these uses, however, is attended with considerable expense. To receive the water of storms, not only must the sewers be very much increased in size, but where an outfall lias to be obtained by pumping, the power to be provided is greatly in excess of that required for ordinary dry weather drainage. Thus considerable additional expense is entailed by the admission of storm water into sewers. Again, the substance which forms deposit in sewers is almost entirely, road grit. This is by far the most difficult of all the matters admitted to sewers to remove to the outfall by suspension in water. Another difficulty arises from the admission of rain water, where the sewage has to be disposed of by irrigation. The farmer is bound to receive the largest quantity of useless sewage precisely at the time when it is most difficult to dispose of it, viz., during heavy rain. The value of sewage farms from this cause is seriously diminished. To prevent inconvenience from this cause it has been in some cases proposed to construct a second system of sewers for rain water, and the more recent practice is to separate wherever it is possible the surface water from the sewage. 26. For the above reasons, and because it is practicable to do so with economy, I would recommend that, in Christchurch the rain water should he removed by the street surface channels to the existing creeks and rivers—the former of which are indispensable under any arrangement, and therefore involve no extra expense —while the creeks are already in existence. A study of the plan of the city and suburbs will show the position of these channels, which carry the water of natural springs, and which cannot be admitted to the sewers. These channels must therefore, either in their present or some improved position, always exist. 27. In addition to these outlets, it has bee® found necessary to excavate a ditch along the Ferry road, for the prevention of floods, and this, together with the channels and the outfall sewer before alluded to, have up to the present time constituted the sole means of draining the entire area. My proposal is, that these means shall continue to he so employed for the removal of the surface water, viz., that of the creeks themselves, as supplied from springs, and the rain water falling on this area; and that such improvements as may be found necessary either to existing channels, or additions thereto, shall be made for the purpose of dealing with surface water on the surface.

28. Under all these considerations, I therefore differ from Mr Carruthers, in not admitting, or only to a very limited extent, the surface waters into the sewers, as he proposed to do. And I would admit the subsoil water into the sewers, whereas Mr Carruthers proposed separately to discharge it into the creeks and rivers by separate pipes laid in the sewer trenches; there would, I think, be some difficulty in keeping them to a regular gradient, and moreover, they could not in most cases drain the soil to so great a depth as the pipe sewers will do, and for the removal of subsoil water, which I hold to be of the greatest importance, would be less efficient. 29, On the subject of the size of sewers I must remark, with reference to the advantages of large sewers on which Mr Carruthers insists, that if a given quantity of water has to pass through a sewer of given inclination, that it is a disadvantage to employ a larger sewer than that which is found to be sufficient for the purpose. This is the argument constantly and properly urged against the admission of rain water, that it necessitates a larger sewer, which is efficient probably for sixty-five days in the year, while for the remaining 300 days the sewer is not only more expensive, but it is less efficient, because larger than is necessary for the work it has to do. Mr Carrhthers’ case can only occur where the laying of a sewer for a small quantity, at an inclination which it is known is insufficient to keep it clean, is unavoidable. In that case, of course deposit occurs, and an occasional flush by a large body of water through a large sewer will clean it when a less body of water would be insufficient to do so.

30. I am aware that Mr Carruthers intended that hia sewers generally should be capable of being flushed, and that he devoted much time and care to arranging his system with this view; also, that the very abundant flushing power which here is available would have enabled him to supply the required quantity, without expense for water or for pumping, in his gravitation scheme. My experience, however, induces me to estimate, as of less importance, the power to flush the sewers than the means, of preventing its necessity, By eliminating road grit from among the substances to be dealt with in the sewers I am enabled to do this, while the abundant water supply of the city and suburbs insures at all times a sufficient flow to render it unnecessary. I, however, by no means undervalue the power of flushing, and in my revision of Mr Carruthers’ pumping scheme, which in its general features, so far as the arrangement of the sewers is concerned, I adopt," I have carefully retained the means of flushing all the sewers, when it can be done from the rivers or creeks without entailing unnecessary depth of a doubtful gradient, 31. At a point on the present outfall sewer, near the Matheson road, where the brickbuilt portion terminates and the open sewer begins, the Drainage Board owns a small paddock of about two and a half acres 3 here, or in its neighbourhood, I would erect the pumping station, for the purpose of pumping the combined sewage and subsoil water through an iron pipe on to the Sandhills, a portion of which would be required to be levelled for the purpose The daily flow would be poured over successive portions of this area, and open ditches and drains would be necessary to carry the effluent water, purified by its passage through 9ft. or 10ft. in thickness of sand, as a minimum, to the Estuary. The land is of an exceedingly absorbent character, and the area is abundantly large for any probable extension of the City of Christchurch. The action of the sewage will be to cause a deposit within the first few inches in thickness of the sand, as is the case in an ordinary filter,'on which grass will grow luxuriantly, when occasionally watered, as here it could be, and still within the limits of saturation.

32. I may now more particularly examine the quantities of drainage fluids to be dealt with, and the dimensions which it will be necessary to give the sewers, with the falls obtainable. I learn 'from Mr Bell, engineer to the Board, that he estimates the quantity of artesian water now discharged at 350 cubic feet per minute, which amounts to a daily supply of 144 gallons per head of the 22,000 population. This artesian supply may probably increase somewhat, but inasmuch as it would furnish three times the present population, or 66,000 persons, with what is usually estimated as a good supply of forty-eight gallons per day, it is probable that the supply from this source will uot largely increase. 33. As, however, it is necessary to consider what may he required in the future, I propose to estimate the required capacity in in another manner. It is usual to estimate about forty-seven as the population per acre in town areas, and thirty-one in the suburban districts. In Christchurch this will be — In the city 950 x 47=44,650 population Suburbs 1500 x 31—46,500 „ Total ... 91,150 „ Allowing fifty gallons=& cubic feet of water supply per head, half of which may be considered as delivered in four hours; this would amount to 91,150x8 Irio ~ „ . . CO x i ~j~?~l519. cubic feet per minute Or something mow tliau Ion? times tfco

present flow of 350 cubic feet per minute. This, however, assumes that the flow continues for four hours only out of the twentyfour when the sewers would be conveying the maximum quantity, and according to this estimate, it would be reduced during the twenty hours to 4-20ths=l-sth of the quantity; at such times, therefore, viz,, during twenty hours each day, there would be ample accommodation for the subsoil water, which would enter the sewers at all times when they are not fully charged. The total capacity of the system would be — cub. ft. gallons.

To remove in 24 hours 1,787,360 or 11,171,000 Of which the sewage would be (with a population of 91,000) 729.200 or 4,575,000 Thus, in addition to the sewage, the sewers would be capable of'removing subsoil water and other fluids, to the extent of 6,596,000 gallons in twenty-four hours. This 1 consider to be ample for the subsoil water and for all purposes, even a portion of the surface water when required; but if rain water be admitted at tbe rate of i inch per twenty four hours over the entire area, the capacity of the sewers would require to be doubled. 34. After a careful examination of the plan and levels of Christchurch, I have adopted the level 30 feet over datum, or 4 3 feet below high water line in the Estuary, which Mr Oarruthers by his gravitation scheme, found to be necessary at the point above referred to—that is, 6 4 feet below the level of the bottom of the outfall sewer at that point. This level I find to be necessary to give the necessary depths and inclinations to the system of sewers within the area to be drained.

35. Starting from the point on the present outfall, where the pumping station will be placed, the sewer follows its course to the East Belt, a distance of 50 chains, at a gradient of 3ft. Gin. per mile. From this point the sewer on the East Belt rises to the South Belt, and to Kilmore street at 4ft. per mile. Along Kilmore street, crossing the river by a syphon, and extending to Colombo street, it rises with the same gradient. Along Madras street to the ISTorth belt, and along North belt to Colombo road, it rises at the rate of lin 880. Along South belt to Madras street the rise is lin 700. On the west of the river from Cashel street to Colombo street it is 1 in 570, and aloug Tuam street it is 1 in 550. In all other cases the inclination is 10ft. per mile and upwards, but generally 14ft. per mile, or 1-300. In the table in appendix, the length, dimension, and depth will be found, and the particulars of the entire system. 36. Blaus No. 1 and No. 1a show the general arrangement of the scheme, which comprises the following : Concrete and brick sewer—--4-6 x 5 = 2,980 ft. 3- x 4,6 = , 3,230 ft, 2-8 x 4 = 1,750 ft. 2' 6 x 3*9 = 1.640 ft. 22 x 3-3 = I,oooft. 2- x 3 = 3,160 ft 1-10 x 2 9 = 1,600 ft. 1-Bx23= ' 3,210 ft. Pipe sewer—18in. = ... 3,670 ft. 15in. 12in. = ... 21,030 or 4 miles nearly. 9in. = ... 236,940 or 45 miles nearly. Total ... 300,315 ft. or 57 miles nearly. 37. The Sandhills, as nearly as can be ascertained, lie below a level of 51ft, over datum* high water in the Estuary is 33'5ft. over datum ; maximum high water iu the sea is 3428 ft. over datum; the rise of the tide is 6ft. 9in.), —and a head of 2ft. above this will enable the sewage to be carried over the entire area. The level of the invert of the main sewer at the pumping station is 30ft. over datum; the lift of the pumps will therefore be from 30 to 53, or a height of 23ft., while the lift into the present open sewer leading to the Estjzary is 6|ft. only. 38. The quantity to be lifted as represented by the water supply is large, 350 cubic feet per minute, or about three times the quantity usually supplied to a population of 22,000. In addition to this, the subsoil water will require to be lifted. If tbe artesian tube wells could be closed even during the night, a very considerable economy in the useless pumping of clear water would be effected ; in the estimate, however, I have provided for pumping continuously day and night. 39. The channel from the pumps to the Sandhills, I would advise should be a eastiron pipe, and, for the present, one of 24in. diameter would he sufficient; its length will be 145 chains, and it will terminate in a small tank, where the surface or “carrier” channels for the distribution of the sewage would commence.

40. To lift the quantity and overcome the friction through the pipe, a 25-horse-power engine will be required, and this should be provided in duplicate. These arrangements will, I believe, be found sufficient until a large increase of the water supply occurs, when additional power and capacity of outlet channel will be required, which it is not immediately necessary to provide. Where coals are expensive, as in Christchurch, it is economical to adopt the most perfect bind of machinery, even though the first cost is greater, and in the estimate for the engines this is provided for—viz., for compound engines working at a high rate of expansion, and calculated not to consume more than 31b. of coal per horse-power indicated. The pumps may be either centrifugal or reciprocating : the latter is the most expensive, and is provided for in the estimate; the engine-house will be a plain inexpensive building. 41. It is probable that apprehension will arise as to a nuisance which will be caused in the neighborhood of the pumping station; this, however, will he avoided. I annex a sketch, plan Ho. 5, of an arrangement of centrifugal pumps, where three pumps are fixed in an iron tank adjacent to the covered pumpwell, into which the main sewer discharges. It will be seen that the sewage is perfectly enclosed in brickwork, and that the pumping operation exposes no surface of the sewage whatever to the open air. It is drawn through the suction-pipe, and forced through the iron case of the pump direct into the pipe leading to the Sandhills, while the ventilating flue from the pump-well will carry the gases into the engine furnace and chimney shaft, and this is the only outlet by which the atmosphere of the pump-well and sewers will communicate with the outer air. The means are thus available for constantly purifying the air through a furnace, which will effectually prevent any nuisance arising in the neighborhood of the pumping station. It is not intended that this is to be the precise arrangement which will be followed, but it illustrates in a convenient way the principle which will be followed in designing the pumping arrangements. ' 42. The majority of the towns in England where the disposal of the sewage is effected by irrigation have paid very largo prices for the land required, and the rental has generallv exceeded £5 per acre per annum. Christchurch is in this respect greatly favored, having within a comparatively short distance a sufficient area for all its requirements, present and future, reserved, and without cost to the community. A very great advantage ; and there can be no doubt -whatever that after the first expense of conducting the sewage on to the Sandhills, it will very speedily pay all expenses of distribution, I have therefore only to add to the estimate a sum wherewith to commence the irrigating operations in one main “ carrier” and a drainage channel. The Board will probably be disposed to grant a lease of the land or a portion thereof for a limited number of years at a nominal rent, npon condition that the area is brought into cultivation, and the sewage disposed of in a satisfactory manner. 43. The high level of the Sandhills is very advantageous to the perfect disposal of the sewage, as it insures a great depth of dry sand and rapid absorption. The area over which the sewage is at any time passing, will not exceed seven or eight acres. All the other portions of the irrigation area will remain as dry as the adjacent country. I am perfectly aware that a natural apprehension may b,e felt by those who are not familiar with the subject, that the concentrating the sewage of a city on such an area is a questionably m98»9 of disposal, but I think it will bh

admitted that of all other means available it is the best. I also know from experience and observation, that in an agricultural district such as the Sandhills, if the sewage be kept in motion till it reaches the land where it is at once absorbed, not the slightest nuisance or danger need be apprehended, and that the disposal of the sewage of Christchurch in the manner here ridicated, may be effected so as to sat isfy the' most critical judgment. Ido not attempt to describe the agricultural part of the question ; undoubtedly land so cultivated will be suitable for market gardens, for root crops, and for grazing, and will attain a value which laud without the means of similar irrigation does not possess. The sewage, lifted as is here intended, would command also any of the adjacent laud, where it maybe considered desirable to convey it, 44. The system of .sewers above recommended will, I believe, drain very effectively the subsoil of the area in which they are constructed. When, as is the case here, the subsoil is of a sandy character, the influence of any one of them will be exercised over a very considerable breadth of area; their united action will be to diminish the exhalation from the present damp soil, and in this manner they will exert a very beneficial effect on the health of the population. They will also enable every house to be drained by a covered pipe drain, and admit of the removal of the excreta of the population in a convenient, efficient, and economical manner, I by no means desire to ignore the fact that great difficulty will be found in carrying out the works in a soil so saturated as is that of Christchurch ; that occasionally permanent running springs may be encountered which it will he impossible to admit into the sewers ; in such cases, it will he necessary to collect these waters and convey them to the nearest creek or river, and in their vicinity to protect the sewer pipe with an additional amount of concrete "and shingle. Also, to make the joints carefully to exclude the spring water from the pipes, ail of which it is practicable to do. For the rest, the drainage of saturated land is chiefly difficult at the commencement of the operation, while the benefit arising from a dryer site to the habitations is incalculable.

45. In making these proposals to the Board I do not intend to intimate that there is an immediate and pressing necessity for the execution of the entire scheme. The drainage area, nearly four square miles*—(* This does not, as I believe, include the entire area under the jurisdiction of the district Drainage Board, but it would not, I am of opinion, be desirable to include any larger area in the present scheme. Whatever may be required will probably be of a rural character, and should be separately dealt with by your engineer.)—is very large, and the population over a very considerable portion is so thin and scattered that the works may in such cases he deferred ; while, on the other hand, there are portions of the area where the drainage is more especially required than in others—thus, in the neighborhood of the Hospital, at Waltham, and in those parts of the area where the artesian water does not rise to the surface, and the removal of the sewage by flushing through the side channels in the street cannot bo effected, there the drainage works are especially required. 46. Desirable as is the drainage of the subsoil of the entire area, I am quite aware that the expenses of the work to a comparatively small population would be felt oppressive under these circumstances the operations of the Board would he to construct the outfall arrangements and arteries of the system leading to the localities where the population is most dense, and where drainage is more especially required, leaving the minor street sewers to be constructed in such order as the exigencies of each case may demand. The possession of a genei'al scheme for the whole area will enable the Board to do this systematically and correctly. 47. With reference to the prejudice which exists against the removal Of excreta by running water, it is scarcely necessary here to enlarge. The system is extending wherever drainage and water supply works are constructed. Paris and London are instances: in the one, night-soil is excluded; in the other, admitted; in Paris, the exclusion entails nuisance and expense by its storage under the houses and separate removal, while London is the healthiest of the large cities of the world.

48. The cost of the system of sewers is entirely unaffected by the admission or exclusion of excreta Having therefore constructed the sewers, to omit this use of them il to forego one of their most valuable advantages. Undoubtedly, for a considerable time to come, the pan system must be continued, and more or less till the sewer system is completed ; but to deny the use of the sewers for this purpose to those of the ratepayers who desire it, would be to deprive them of an advantage for which they pay their share of the cost, and have a right to the full measure of benefit so purchased. 49. The objections to the use of sewers for the purpose of conveying excreta has no force where, as is here intended, they have sufficient fall to secure their self-cleansing action ; moreover, the removal of the sewage matter to the Sandhills, will admit of its perfect disposal by absorption and the growth of plants, &c., while no impurity whatever will be discharged either into the river or Estuary.

50. As a matter of cost, the covered pipe drains 4in. diameter (which is generally sufficient for house drains), at Is per foot, will not exceed the cost of a surface drain. If well laid and properly jointed, they will remove all the fluid filth from the moment of its admission, perfectly and speedily to the sewer; and by leaving a small portion at the top of the joint of the pipe to be stuffed with, clay instead of cement, the subsoil water will also gain admission. I am aware that the removal of excreta by the house drains is strongly opposed by some persons, but I am certain the opposition proceeds from an entire misapprehension as to what are the simple and inexpensive means necessary to effect it. Where water is obtained under pressure, and is expensive, purchased at a certain rate per 1000 gallons, where special cisterns, valves, &c., are necessary, the water-closets may cost £6 each. In Christchurch, however, where water is procured in abundance, a very much more simple arrangement may be made. 51. This arrangement can be constructed under an ordinary privy seat by a bricklayer, and consists of a small, cement-lined, brick tank with a sloping bottom; its length is about 3ft., and it is made to contain about 10 or 12 gallons of water. At the lower end of this tank, which is about 15in. or 18in. wide, a circular cast-iron socket is fixed, 4in. in diameter, which communicates with the house drain. This socket is closed by a wooden plug with an iron handle, extending above the seat; the plug is hollow and about lOin. in height, terminating at the top level of the water which the tank is to contain. Waste water from the artesian supply is admitted to the tank, which, when full, overflows through the hollow plug. After one or more uses of the place, the plug may be lifted by the handlers* and the entire contents of the tank discharged through the house drain to the sewer ; nothing more is then required but to replace the plug in its proper position. To prevent stones, bricks, and improper substances of that nature from entering the house drain, an ordinary dip trap is constructed outside the privy, and when obstructions occur which such matters would cause, they can easily be removed by lifting the cover. The abundance of waste water at all times available for the purpose here will ensure the places being at all times efficiently flushed and in good order. These water privies act perfectly, are inexpensive (about £2 10?) and simple, requiring no plumber’s work whatever. A sketch of the arrangement is given on plan No. 7. The use of this arrangement will, I am quite certain, require no enforcement; the comfort, cleanliness, and the absence of a payment of 7d per week, will be quite sufficient to ensure its adoption by a large majority of the population.

52. The greater part of the material required for the sewers will be stoneware pipes. To ensure their durability and proper action, these should be of the very best quality—no soft pipes should under any circumstances be used. The material of properly burned and glazed pipes is indestrmrtible, and entirely non-absorbent, the glazed surface affords no fool bold to rats, which avoid them, while in brick sewers they are ooctosiwi&ily troublesome and dwb’uoUre. Th®

pipes should not only be of good material, but their shape should be as nearly perfect ns possible, straight in their length and truly circular, each spigot end fitting accurately into the socket of the adjoining pipe without “ lip ” or irregularity of level at the junction. The joints should be made with good Portland cement, so as to be watertight, and any cement which may be forced into the interior of the pipe in making the joint should be at once carefully wiped out. 53. The pipes should be laid in straight lines, and where any devifftion from the straight line occurs, a “ man hole ” should be constructed. These “man holes” also form junctions for other pipe sewers; the arrangement is shown on Plan No. 3. One of these “ man holes ” is provided for every 250 ft. in length of pipe sewer. Their use is to facilitate the examination of the sewers before they are brought into use ; also the examination and cleansing, should it be required, in the future. 54. At these “man holes” the subsoil ■Water would be admitted. The trench in which the pipe is laid will always collect the water from the ground on either side of it, and if a patch of shingle be laid near the “ man hole,” and a small earthen pipe carried ' from it through the brickwork into the “ man ■ hole,” the water collecting in the shingle will be discharged into the sewer, and mingle with the stream. The shingle will keep back the sand; and, should occasion require it, the pipe can be stopped, and the water from the exterior excluded. The subsoil water can also be admitted into the sewers at other fioints, by inserting at intervals a special ength of pipe with an aperture and perforated plug, covered with shingle. This is shown on Plan No. 2.

55. The pipe sewers should be bedded in 6in. to Sin, of concrete, carried high enough just to cover them. Every care should be taken to get out the bottom of the trench with regularity, so as to preserve a uniform thickness of concrete beneath the pipe; its use being to prevent any displacement or irregularity of settlement of the pipes when the weight of the earth comes upon them. 56. The junction pipes for house drains, &e., should as far as possible be inserted when the pipe is laid ; the end of the branch, when not immediately used, being carefully and securely stopped with a suitable stoneware plug and clay, to prevent the entrance of the surrounding soil. An occasional half-socket pipe may also be inserted with advantage where junctions are likely to be required. This will admit of a length being taken out generally without breakage ; there is always some risk that the pipe line when disturbed for the purpose of making connections will not be replaced with the same solidity and accuracy as when originally laid. Special pipes are made by some manufacturers to overcome this difficulty ; they are somewhat more expensive, but I have always found that with care competent workmen can, with the arrangements I have alluded to above, do all that is necessary. 57. It is however important that only qualified workmen in the employ of the Board should be permitted to make the connections with the public sewers, and that not only the material, but the workmanship to the private drains which are to be connected with the public sewers should be subject to official inspection and approval. Those tradesmen only who have proved their competence to do the work, and who hold licenses from the authorities, should be permitted to undertake the house drainage work. 58. Those sewers which are so large as to exceed the pipe sizes can either be made in concrete or brickwork; cement, not lime, should be used in either case, with hard, nonabsorbent material. The brickwork should be of the very best quality. Where any spaces or broken ground at the back of the brickwork occurs in the construction of the sewer, it should be filled in entirely with concrete and shingle, back to the solid ground; it should not be refilled with the original soil, or the sewer will crack and probably get out of shape. The size of the biggest sewer required is not large, 9in. work will be sufficient; but it should be backed with concrete, and a thickness of 6in. up to the springing of the arch is included in the estimate. The interior should be rendered with cement up to the same level, and the work in the arch carefully pointed. Stoneware invert blocks, set in concrete, as shown on plan No. 2, are a great improvement, and facilitate the drainage of the work when in progress. 59. When these are not used, and water appears in the trench, it is necessary to lay a drain pipe in concrete or shingle to carry it off, so as to insure good work in the invert. The extra expense will be more than repaid by the quality of the work obtained. This pipe may be retained for the purpose of collecting the subsoil water after the sewer is in operation. When this is not done, agricultural drain pipes lin. in diameter should be built through the brickwork a little below the springing of the arch, at intervals of about 50it. in the side of the sewer, with a patch of shingle on the outside to collect the water and prevent the entrance of sand. 60. Flushing is an operation which is often considered as absolutely necessary to the proper condition and action of the sewers, as it is affirmed that they are unable to discharge without some such aid the matter which finds access to them. This, however, is not the case where there is an abundant water supply for domestic purposes, and tke sewers are so constructed as not to allow of its leakage into the surrounding soil. There is no tendency to deposit if, as is here intended, the road surface water is excluded ; for then the material which constitutes deposit in sewers, viz., road grit, is also excluded. The man-holes can at all times be used for the purpose if needed, and no further special arrangement for the flashing of the sewers is required. Solid refuse, which must be removed in the dust cart, or by the scavengers, should not find access to the sewers. Every inlet except the water-closet pipe which is trapped, will be protected by an iron gird and trap, and it will be impossible to pat such substances into the sewers to interfere with their proper action. 61. In every system of sewers provisions for perfect ventilation must be made. Every cubic foot of fluid which is admitted will displace a similar quantity of air. If no provision be made for escape, the air in the sewer would be under pressure, and tend to force its way through every imperfectly trapped inlet which may be existing; and jhould such inlet be within the house, ti e atmosphere thereof would be vitiated. It is explained below that direct communication between the houses and the sewers should not, except in the case of water-closets, be made. The usual nieans of ventilation is shown in the Plan No. 3. A small brickwork box is constructed in connection with a man-hole, at or near the centre of the street. The air in escaping passes through a basket of charcoal, and afterwards through an iron gird fixed at the level of the street surface. The charcoal is intended to render the air inodorous. The arrangement also provides that any water which may enter the gird, shall pass on with the current in the sewer, but the road grit will be arrested, and will require occasional removal. These ventilators should bo fixed at convenient places, five or six hundred feet apart. . „ 62. A more active ventilation has in some cases' been attempted by connecting the sewers with the furnace or chimney of manufacturing establishments, the proprietors of which may be willing to permit it. Undoubtedly a more rapio change of the air of the sewer would thus be enacted, as the draught would be promoted by the heated chimney. Another means which may be adopted is to take a pipe from a man-hole situated Jjear to a wall —not that of a dwelling-house—and to affix a vertical pipe thereto of any convenient height; free escape of the air may thus be obtained. Practically, however, if the sewer bo properly constructed, so that no stagnation occurs in the flow of the sewage, and its removal bo effected before decomposition takes ■place, all that is actually required is a free passage for the inlet and the outlet of the uir t the street surface. 63. Among the objections which have been frequently made to a system of sewers for towns is one “ that the house drains act similarly' to the gas pipes, except that in Hie latter case illuminating gas is conveyed into tJui interior of a house for a useful purpose j by the other, malarious gases find access, which engender fevers,” &c., &c. The sewers are ‘ in fu-t, considered in the light S f >d »n im-vitablo nimajme/ The

cases, are, however, widely different. The cesspool means stagnant filth stored for months, and in a state of active decomposition. The sewer, if properly constructed, means constant removal before decomposition can take place. If any stagnation should occur in the future sewers of Christchurch it will be due to errors of construction.

64. The usual points in a house to which the drainage requires to be carried are—lst, kitchen sink ; 2nd, wateer-closet; 3rd, stopcock in the paved yard, where water may be drawn for washing carriages, &c.; 4th, where, after use, it can be removed ; sth, the stable; and 6th, rain-water pipes. If the Ist and 6th cases the pipe can be brought down on the wall of the house, and should terminate a few inches above the trapped opening, as is shown in plan No. 6; in 3,4, and 5 a similar grating and trap placed in the yard surface, or in the stable, will receive the water. For all these cases it is impossible that the sewage gas can enter the house, as they have no direct connection with it. The 2nd point, viz., the water-closet, is the only one having a direct connection. In this case, if the soil pipe be carried for its full size up to the top of the house, and a syphon tap be fixed at its lower end, the ventilation of the pipe will be perfect, and the danger of gas entering the house will be reduced to a minimum. The arrangement is shown on plan No. 6. The principle is simple, if the proprietors of houses will only insist on its being carried out.

65. Where there are several branches to the house drains it is desirable to carry them all to one point, as shown at PT on the plan. This should be trapped by a similar arrangement of dip-trap, and, if carried up to near the surface, can be readily opened for inspection. If this be done, no further trapping at the junction of the house-drain with the public sewer will be required. A direct communication from this trap to some convenient wall, where a ventilating pipe (not near to a window) can be fixed, is desirable, as it removes all chance of pressure within the pipe, and ensures a perfect ventilation. Stackpipes are commonly used for this duty, but this is not to be recommended, as at the time the stackpipe is discharging rain water downwards it 'does not readily admit of the upward escape of the air which is then necessary.

66. In carrying out the works, doubtless some modifications will be made. On the general plan, which accompanies this report, the sewers are shown as in the streets, and, doubtless, the principal sewers must there be constructed. For many of the minor sewers, however, this need not be. The sewers will not have to carry off the street surface drainage, and for that purpose will not there be required. 67. The points where drains are generally wanted are at the back of the house, and where it is conveniently practicable, very great economy in the house drains, as well as efficiency, will be obtained by placing the public sewer there also. This arrangement, or what is called “ back drainage,” is most economical and applicable where the houses are in continuous rows, or nearly so ; in that case the necessity for conveying the house drain under the house, which is always undesirable, is avoided. Christchurch, at present, contains but few localities of this character. Plan No. 4, however, illustrates the principle recommended, and even in the case where the houses are very few in number, this arrangement is worthy of consideration, 68. All the main drains in the scheme’ are shown to be 9in. diameter. For a very large portion of the length 6in. would be amply sufficient to carry all that will be required of them. The difference in the price of the 6in. and 9in. pipe laid, however, is so very small that, the larger size has been adopted for the estimate. In the event, however, of the above plan being carried out, I would recommend two 6in. pipes for back drainage to be substituted for the one 9in. pipe in the street.

69. For improving the present means of carrying off the rain water and surface drainage, Mr Bell is of opinion that the following works would be required, and the cost, £19,128, is included in the estimate. To drain the large quantity of rain water which collects in the district of Waltham, near the Gasworks, it is proposed to divert it from its present courae down the Ferry road, by deepening out a portion of the old bed of Jackson’s Creek, and cutting a new drain where necessary, to straighten it. Into the stormwater channel will be drained the water from the sewer in the south-west and the south city drain, the water from Gasworks stone drain and its large pipe in Third street, which pipe and the stone drain would be put into a thorough state of repair. A pipe drain would be laid in the old Antigua street drain to the river, taking all rain water from South Addington ; and the open drain on the Park side of Lincoln road would be kept open as it is at pretent. When these are all constructed, there would be no further use for the south city drain, which could be filled up, The present brick sewer would be used for taking away rain water from the north-east and central parts of the city. The water from these districts would be collected at Madras street, and carried in a brick culvert to the river. The water in the North Bolt drain would by this means be lowered, and might be covered in if found necessary. Free’s Creek in the Springfield district would only be covered in by a pipe where necessary. East Belt next to the cemetery would receive a 15in. pipe to the river, to convey the rain water from Upper Bingsland and Packe’s road district. Bt, Albans Creek would receive the drain along the north side of the Edgeware road, covered in by an 18in, pipe; it would also receive the drain on the St. Albans lane, covered in by a Isin. pipe, if necessary. The lower part of Knightstown would also be drained into St. Albans Creek by a pipe drain. St. Albans Creek would be deepened if necessary, to give good drainage for rain water. Ferry road would receive a 12in. pipe from Matheson’s road to Bell’s Creek, to carry both the rain water and the' house drainage from dwellings along the road, and the mouth of Bell’s Creek would be deepened to give this pipe the requisite fall. Outfall brick sewer might be reconstructed of a smaller size which would be permissible, as most of the storm water which it carries at present would then be diverted from it into ofcjmr channels. 70. The estimate for the works before des-

The annual value of the premises on the area proposed to ba drained is £235,249, and is rapidly increasing, One shilling in the £ per annum on this value will yield £11,762, or very nearly the annual sum required for

payment of interest and working expenses. A loan obtained at 5 per cent, to be repaid in fifty years, would require an annual payment of £5 9s 6fd per cent., or 5£ per cent, per annum.

71. As it is probable that some further powers will be required by the Board when carrying out these works I would recommend for consideration those clauses of the Public Health Act of England, 11 and 12 Victoria, 1848, which refer to the construction and maintenance of sewers and the drainage of private houses, Sections 43 to 49 inclusive, by which power is given to take works through any place or land whatever, making compensation for damage. 72. In Christchurch there are at present but few cellars; their construction is, however, on the increase. And in order that damp unhealthy houses should not be ei'eeted, it is very important that their construction should be subject to proper regulation. Sections 51 to 54 of the above Act provides for these regulations, and empowers the Local Board to fix the level of the cellar and lowest floors of houses to be erected. The depth is regulated by that of the adjacent sewer, and must be such as the sewer will effectually drain; 2ft. or 3ft. above the invert will generally be sufficient to keep the cellar dry. The possession of the general scheme for the city will thus enable the Board to regulate the depth of cellars. These clauses also refer to the proper construction and management of cesspools, privies, &c. The rating clauses also are worthy of consideration. The special district rates give the power to the Board to levy rates on districts especially benefitted by any particular drain. 73. The power to levy private improvement rates I have found to be very useful and acceptable to the ratepayers. These rates are for the purpose of recouping the Board for any works and necessary improvements to private property which the owner may be unable or unwilling to do, and the Board have executed. In these cases the outlay is secured as a first charge on the property, and provides that principal and interest shall be repaid in a limited number of years. W. Clahk, Member of the Institute of Civil Engineers. For the purpose of illustrating this report, the following plans have been prepared : 1. General plan of the city, showing position and direction of sewers and pumping station. IA. Plan showing outfall and irrigation area, 2. Section of brick-work and pipe sewers, with inlets for sub-soil water. 3. Plans and sections of man-holes, ventilators, &c. 4. Block plan showing back drainage. 5. Diagram showing pumping tanks, &c. 6. Diagram showing general arrangement ment of house drainage. 7. Plan and section of water-privy.

*Yeab 1876. Provincial Districts. Estimated Population. Annual Total Deaths. Annual Deaths per 1,000. Auckland Wellington Nelson Westland Canterbury ... Otago 80,934 41,591 25,100 16,655 81,389 112,624 1,141 654 279 166 1,018 1,302 14-09 15 07 11*11 9-09 12-41 11-56 Towns. Estimated Population. Annual Total Deaths. Annual Deaths per 1,000. Auckland Wellington Nelson Hokitika Christchurch ... Dunedin 12,156 15,145 5,573 2,983 12,371 22,567 303 299 98 53 280 389 24-93 19-74 17 58 17-77 22-63 17 24

cribed is as follows £ 8. d. For 57 miles of sewers, as per statement 132,805 0 0 Two s'v phons under the river 1,200 0 0 Pumping station, including two 25 h.p, engines, boilers, pumps, and pump well ... 8,500 0 0 24in. iron pipe to Sandhills.., 8,000 0 0 Levelling Sandhills, carrier, drains, &c. 2,000 0 0 Houses for workmen 1,000 0 0 Storm overflows at Waltham and other places, &c., &c.j for improvement of present surface drainage 19,128 0 0 172,633 0 0 Contingencies, engineering, &c,, 10 cent 17,263 0 0 Total £189,896 0 0 Working Expenses— Fuel at T3 tons per day, coal 38s per ton, 475 tons per annum 850 0 0 Oil, tallow, and waste 130 0 0 Establishment— 1 engineer at £310s per week and residence 1 assistant at £3 per week and residence 1 laborer at £2 per week and residence Per week £8 10s. Per annum 442 0 0 Eepairs and depreciation ... 200 0 0 Total, per annum ... £1,622 0 0 Total Annual Charges — Interest on £ 1 90,000 @ 5 i r j> cent 10,450 0 0 Working expenses 1,650 0 0 Total, per annum ... £12,100 0 0