THE CITY BRAINAGE

Evening Star, Issue 12398, 11 January 1905, Page 7

THE CITY BRAINAGE

ENGINEER'S REPORT.

_TJte. following report and covering letter .flgr;.Mt/.JE*T. Noble Anderson, submitted at last nigh't'a meeting of the Drainage and Sewerage Board, will be dealt with at the nesfe meeting of the Board:— Dunedin,' January 10,, 1905. < As verbally explained, owing to the practical aspects of the question,. an exact account to the end of the year could hot be prepared .till a week or so later j consequently this report is made from regard to the state of work durujg the fortnight before Christmas. - tThfortuDately this makeg certain of the works, in hand appear much more expensive than they other- «», should,, since the.heayy initial expense on such things as material and special appliances had practically* no works to set •against them.

I would like to explain with reference to lay estimate of December 5, 1902, whicli has been, used as,a basis in most of the comparisons, that the sum of £6,500 which was, omitted from that estimate was not funded, interest, as. might be assumed owing to. the fact that the Board have now decided to take advantage of that clause. of the Act which empowers them to fund certain items of interest, but was merely a rough estimate of preliminary expenses which would probably be incurred before the Board's loan works as then foreshadowed could be started,

Further, I would explain that lack of time, has prevented me from dealing in detail with some minor items of expenditure. I trust that in this, as any other omission or error that may be found, it will be understood that, whatever the error may be, it is not due to will on niv part nor want of zeal on the part of the Board's staff.—l am, etc., J. T. Noble Andeeson.

WORKS DONE UP TO DECEMBER 15. In.the following report a distinction is drawn between " drains " and '' sewers"— drains being such sewers as are mainly intended for surface water drainage, and sewers those which are intended mainly to carry sewage. Preface.—The Dunedin Drainage Board wore constituted by statute in October, 1900. All existing drains were vested in them! Until June, ISO 3, however, no new works were commenced. Consequently, of the Board's expenditure to date the sum of £19,783 which appears under the general account represents the general expendion all recurring charges, including repairs, for more than four, years, on the old existing drains; while of the loan expenditure of £85,917 4s 3d about £BO,OOO has been spent on works, investigations, and other charges incidental thereto, while the balance was already expanded in sundry preliminaries prior to June, 1903. Old Works.—Approximately half of the drains in the district are of masonry or earthenware, with an average age of about twenty-two years, and are in such condition that they may be considered as likely to be serviceable for a considerable" time ; while the rest are of timber or obsolete types of earthenware. The expenditure in maintenance and repairs on old works is necessarily very heavy, and two lines of policy were presented to the Board, one of which was to abandon all ttie existing works and to lay over 100 miles of sewers throughout the district, about forty miles of which would be in duplication of existing old drains. The Board, however, chose the scheme of works which conserves the maximum possible amount of the old drains, and which will require less than sixty miles of new drains and sewers to be constructed to serve the same population.

The policy adopted by the Board is therefore the same as what is usually adopted in Great Britain when replacing "or enlarging existing drainage works so as to meet present day demands. This is that the old works are conserved as long as possible, and when they are at last in the state of actual collapse they are then renewed by structures of a more permanent character, and thoroughly up to date. That this is the most economical mode of working will be appreciated by every owner of existing appliances in the district, who can argue from his own particular case where he would no doubt find that it would suit his pocket to hold on to his old possessions as long as possible before replacing them. And obviously exactly the* same economic problem ■applies to the whole district as applies to the individual. In this connection it is perhaps not out of place to state that the Board's policy has been less appreciated by the pnblic than might have been expected, and the general experience of the Board's plumbing inspectors is that builders nnd householders, when effecting repairs, instead of taking advantage of the Board's policy, embark at once on the full expense of bringing their drains, sanitary appliances, and everything connected therewith into complete" accord with the Drainage Board's by-laws every time it becomes necessary to make any alteration. Returning to the question of the Board's policy, the experience has been that in. a large number of places the drains have had to oe renewed, and consequently the expenditure on this account out of the general maintenance fund (rates) has been very heavy. And the prospect is that for some time to come the annual expenses under this heading will be heavy. This is an annual expenditure, however, which should steadily decrease from year to year. In the meantime, however, the rates will be higher owing to this cause than the normal, or than they Bhould ultimately be.. It is very difficult to estimate what may be the value to the Board of the old drains which they take over from the different local authorities; but one point- is very clear—namely, that whatever the gain may be, the body which will, benefit by it is the City Council, including Caversham. For this reason, that the Board are under obligation to pay interest on the value to them of all such works as their scheme enables them to utilise. The Board's policy, therefore, in electing to retain old works has been dictated from regard to the circumstances of the whole community, and the effect of it will be to relievo the municipal authorities of a considerable portion of their former annual outlay, both for labor and interest on loans. In this policy the Board can claim to have taken a broad and liberal view of their duties. The opponents of the continuance of the exitting system of combined sewers raised two points—first that the drains were not " suitable for modern, sewage work" ; second, that they do not give a self-cleans-ing velocity, owing to the flow of sewage in them being exceedingly small. When proper trapped connections are made theso drains can safely bo used, and the few which cannot be made self-cleansing will be abandoned. In the meantime, the continuous work of three men and a dirt cart .is employed owing to this cause, and three more men are contincouely employed in keeping the timber drains and outlets hi order. Both of these heavy causes of expense will gradually disappear. The Dunedin conditions are eminently suited for the combined system, as here, unlike Continental cities, the rainfall is so equally distributed that even where the wafer supply is deficient the drains are always sure to get a good flushing before they can become dangerous. The rainfall records clearly show that periods of drought are very unlikely to occur; in fact, it* is less than one month out of every forty that fails to give at least one rainfall of sufficient weight to amply flush all reasonablesized drains. Consequently, the Dunedin climatic conditions are peculiarly fitted to enable it to enjoy the advantages of the combined system of sewering. And to theso advantages is the fact that the main sewers, .Icing constructed at least six times the capacity which would otherwise suffice, it is only necessary to provide Dverflows on the sewers_, eo that all excess of rainfall above a certain amount may pass out of the sewers,'and these main Eewefs can be made ultimately to serve at least five times the population for which they were first intended. Here such overflow can readily be provided .into the harbor. As 1 , however, the Harbor Board, to avoid solid matter of any kind finding its way into the harbor, have .compelled your Board *° P,r°yide for the removal of all rainfall up to three inches a day by tne sewers, the only" way in which such overflows are perW'tel, by the Harbor Board is when they make provision to remove all solids. ~ %**■ provision for this is made in the. case of the Frederick street sewer, where two detritus tanks have been conetructed. And as the sewage increases in

volume, so as to make lees room in the sewers for storm water discharge, the increase in population can from time to time be met by the increase in the number of detritus tanks.

is satisfactory to record that these tanks are proving efficient, and that the cost of keeping them clear of solids is considerably cheaper than was at first estimated.

The various works undertaken are described in detail in the appendices to this report. In those many modern inventions have been adopted to effect economies or to do what m the past would have been impossible. These detritus tanks may be claimed to fill both of these functions, because they not only enable solids to be deposited under conditions which formerly were impossible, but enable works which, under ordinary conditions, would barely suffice to servo a population of 100,000 P«>ple to be increased to suffice for considerably more than a quarter of a million people. And in making provision for eo large a possible increase in population, the noteworthy point is that the scheme throws no heavier burden on the ratepayers • than they would have had to bear if the separate system had been adopted suited to serve a population of 60,000 people. It is possible. that the Dunedin district may never more than double its present population of nearly 55,000, but the whole tendency of modern ciyilsation is for the cities to grow at the expense of. the country, and for the larger cities' to grow at a greater rate than the rate of increase of the whole country. And from this consideration it is hard to estimate on any limit to which the population of Dunedin may not reach.

Before concluding this report, attention is drawn to the fact that the only variation made in the scheme of work on "which the 1902 estimates were made has been the abandonment of the proposal to use septic tanks in the case of certain of the lull boroughs, and in place thereof to allow practically all the sewage from the watershed of the harbor to flow by gravitation to the pumping station at 'Musselburgh, and thence to be discharged into the ocean. Ills alteration brings the whole scheme into accord with the original intent. The only reason for the septic tanks having been included in the estimates was that it was feared that the cost of the better scheme which is now adopted might without them have proved prohibitive. Closer investigations, however, and the result of careful design, showed that this great advantage would probably be obtained within the borrowing limits at the disposal of the Board. Tho only case in which any increase above those estimates has occurreo to date has been in the case of pipe lines for branch sewere or reticulation* the branch sewer work will, of course have to be carried out to the full extent then estimated to enable the revenue to be collected. The question of reticulat on, however, will require very close attcnt:on, and no reticulation can be undertaken until it is shown that the particular street to be served will amply repay the expense. Briefly put, on the basis of present expenses, the balance which will be left out of the loan will barely suffice for thirty miles of reticulation, against forty-two originally estimated on. —Preliminary Work.— The British Government have from timo to time laid down standard rules which govern the preliminary work for such schemes as this, which are observed bv municipalities in" the Old Country seeking power to carry out their works, and all these requirements were rigidly followed before the present scheme was adopted by the Board. A brief recital of the general heads of these standard preliminary investigations will help to show what tliis work entailed :

(a) Survey of the District to be Sewered. —This not only included the standard six cham plan, but in the existing urban arear, detailed plans to scales of 40lt to the inch and 100 ft to the inch, as the circumstances required, hav-3 also been prepared. (b) The Records of Rainfall over the District.—This work not only comprised | obtaining til the rainfall records, but also the investigation of all records of flood damages and indications of unusual storms, (c) Character and Physical Outlines of the District.—This work included extensive research by means of trial bores, sinking pits, anl obtaining records from architects, the Government, and local authorities of such excavations as were likely to throw any light on this subject. Also, the preparation of maps showing the physical contours so far as they affect the flow of drainage. <

(d) Present and Prospective Population. —'This work entailed the compilation of all the available records since Dunedin wa.~ I established. These records have been plotted in the form of a diagram, so that they may be readily followed. (e) The Supply of Water to the District. —The City records of this were obtained, and personal visits, under the guidance of the late city engineer (Mr Mirams), were paid to • the works aud the watersheds studied, and the existing sewer and drain discharges measured. (f) The Sanitary Appliances at Present in Operation.—These, along with the existing works, have been very carefully considered. At least two men have been continuously employed for more than two years in studying and testing and recording their conditions, so that nothing should be needlessly rejected. (g) The Position of the Outfall and Mode of Disposal foe Sewage.—This question has been the subject of a Royal Commission, and is still to a certain extent sub judice. In the meantime, however, the course adopted by the Board is in accordance with the finding of the Royal Commission —namely, to make provision for the liquefaction of the sewage by septic action, and then to discharge it into the ocean at deep water. —Existing Works.— The existing sewers have been carried out in accordance with the scheme prepared between the years 1872 and 1878, and schemes for the drainage of the Flat suburbs of Caversham, South Dunedin, and St. Kilda, formulated shortly afterwards by 'Mr Barr and Mr Hay. The works in the City, so fax as they W2re completed, were carried out between the years 1878 and 1884, while the works on the Flat were car- ! ried out about the same time and shortly afterwards. The expenditure on all these works, including masonry, brickwork, and stoneware pipes, as well as more temporary structures, such as flat-bottom wooden sewers, was undoubtedly very heavy. And, in addition to this, the expenditure on sanitary appliances and sewers by private individuals involved an even larger investment of money.

Briefly stated, the existing sewers provide for drainage from the whole of the watershed of the harbor by means of large diains, which follow the course of the original streams and creeks. Those which were constructed by the City proper discharge by four outlets into the harbor and two outlets into the Water of Leith, all of which are of brick and concrete construction; while the sewers from the Flat discharge in four places, all through temporary timber outlets fa fifth discharge has recently been constructed into the harbor for the main Caversham- sewer in concrete). The six sewers in the City were intended to bo intercepted by a main intercepting sewer, which, however, was never carried out.

Tho policy of the Board is now well established, and their history, since adopting this scheme, has been as'follows: •While keeping steadily in view the avoidance of causing unnecessary expense to those who are in possession of sanitary conveniences it was determined that all new sanitary works should be carried out in the safest and most up-to-date rnaniier. A plumbinp inspector with experience of the establishing of modern sanitary practice in Great Britain and Melbourne was appointed. He l-.owever, resigned twelve months ago. To assi't the ratepayers in, efficiently and economically improving their sanitation, the Board then appointed two other skilled and thoroughly up-to-date plumbers, who have been steadily employed ever since in gradually introducing the necessary reforms. Their labors, are rapidly bearing fruit, and by the application of 66nfirraal* suasion and moral influence the desired end is being effected with .the least ultimate expenditure and practically no disturbance to vested interests.

There has been great difficulty in. gettinj

thoroughly up-to-date sanitary appliances.' Standards were imported, but as it was undesirable, on the ground of economy, that plumbers should be limited to one or two standards, a large number of appliances, not quite up to these, have had to be approved. While some of these have features which mark tliem as distinctly inferior in design to the Board's first standards, they are, all good and reliable from regard to workmanship and public health. —New Works.— Owing to the incomplete nature of the records of the progress of building in the city and suourbs, the changed conditions which have followed on modern discoveries and the extension of knowledge in sanitary matters, it was found necessary to survey and investigate all the seven points mentioned in the preface, irrespectively of whatever may have been done before. To a certain extent the result was that the main intercepting sewer was located hi almost the same position as had been intended in 1878 so far as the limits of the City were extended. It, however, was carried to the foreshore of the harbor, at the point where the large Manor place sewer at present discharges, but from thence the surveys and designs were entirely different from what had been previously proposed. Circumstances had made it evident that it was not possible to discharge sewage on the Ocean Beach. A moderately good sewage outlet had," however, been discovered at Lawyer Head, and an excellent outlet further away, on the Bird Island. The cost of conveying the large quantity of combined sewage and storm water to this latter outlet was found to be such, as would exceed the Board's borrowing power, and advantage was therefore taken of Lawyer Head as a stonn-water overflow, the sewer for sewage only being carried on from that point by a small conduit only 4ft 6in wido by 2ft Bin deep, which it was proposed to connect with the Bird Island by a single 3ft diameter pipe. —Summary of Total Loan Expenditure up to 15th December, 1904. Preliminary 'Work — Investigations and detailed surveys £2,493 8 5 Consulting engineers 739 18 2 Eoyal Commission and investigations re Bird Island ... ... 7SB 0 0 Cost of obtaining Acts, etc 559 7 5 Standing ChargesInterest 593 17 11 Salaries and wages 6,133 2 5 Reat3, advertising, travelling, etc 1,850 15 8 Accident insurance (part paid in advance) ... 533 9 2 Miscellaneous Expenditure— Land and building's 2,586 13 2 Plant, tools, and instruments ... 3,818 12 7 To be Refunded— Store 3, quarry, etc 1,013 4 1 Work done for City and others 627 12 11 Accident disbursements ... 57 6 6 Spent Outside District— Repairs to Tomahawk road 190 6 6 Work as per details in Appendix „*. ' _. 64,316 9 4 Total expended to date ... £85,917 4 3 —Summary of Maintenance and General Expenditure.— Maintenance, repairs, and sewer cleansing „ £7,04114 1 Stores „. „ „. 2,681 17 0 Interest on loans „. 1,445 19 5 Salaries and wages „. .„ _ 2,761 4 6 Travelling expenses ... .„ ... 66 9 8 Plant and tools _ „. 283 13 7 Spent outside district „. ... 7 12 1 To be refunded 250 0 3 Secretary's gross disbursements, including elections, rate collection, law costs, compensations, sundry rents, property charges, insurance, etc. ... 5,244 12 9 Total £19,783 "3 4 —Description of Works Done.— Following the order of the- estimate presented to the Board on the sth of December, 1902, the works carried out to date will now bo described in detail. I.—Main Intercepting Sower. Section AA, estimated to cost £2,075. — This section was intended to tap the Water of Leith in Clyde street for flushing purposes. The Water of Leith has b%en tapped at Clydo street, but owing to the abandonment of a proposal to deal with the sewage on the area around Pelichet Bay by the separate system, and the decision to deal with it on the combined system, the main intercepting sewer, instead of starting in Clyde street, has been brought as far back as the eastern side of Dundas street, where it picks up the storm water coming from the direction of the Northern Cemetery, and passing along through Harbor terrace, Albany street school grounds, and the railway reserve passes through Frederick street to the original rout© in Athol place, intercepting all the existing drains on the way. The primary reason for this change of programme was that the existing drains carried such foul sewage that when the Harbor Board reclamation stopped them the condition of affairs which arose was pestilential, and the Board were forced to provide for this sewage. The provision made is that this main intercepting sewer, to cany combined storm water and drainage, has been completed and in the present discharging into tho Frederick street sewer, the level of the water in which 6tands upwards of 10ft above it, and until the main intercepting sewer has been so far completed throughout its whole length this portion will have to continue to act as a siphon,, depending on the flush which is periodically turned on from the Water of Leith at Clyde street to keep it in a sanitary condition and free from obstruction. The cost of this portion of intercepting sewer is returned by the accountant as £1,422 2s sd. The estimated cost of completingi the main intercepting sewer in this section (AA) is £1,200, consequently it will be seen that tho modification to bring this section in under the combined system has cost the Board £547 more than the estimate; but against this it should be remembered that ..the drainage and sewerage of Harbor terrace and the adjoining districts is already provided for, and consequently, to the extent of about £SOO, the provision made under " VIII. branch sewers in City," is reduced. Section 88, estimated to cost £13,800. No work has yet been done on this section. Section CC, estimated to cojt £13,300. No work has yet been done on this section. Section I)D, estimated to cost £IB,OOO. This section carries the main sewer right to tho pumping station, and work has already been carried out in connection with this which has cost to date (15th ult ) £3,911 15s 2d. For this tho following work has. been done: —4ooft has been com-pleted—-202ft in concrete and the balance in Monier pipes—while Monier pipes have been made and are waiting alongside the line of main intercepting sewer to a length of 1.782 ft, and 70 per cent, of the value of all the plant which should suffice to complete the whole of the work in this main intercepting sewer is already on the ground. Summarising the position of tho £34,755 estimated for th s' main" intercepting sewer, £5,333 17s 7d had been spent at tho time these measurements just given were made last month. ll.—Suction Well, etc. When the works were commenced—in the middle of 1905—4 he provision for Eeeping accounts- was only such as wa's required, by tho Act and the requirements of tho Audi-tor-General. When, however, towards the end of the year, the Board found that.it would- be necessary to do a considerable amount of work by day labor, steps were taken' to inaugurate an engineer-in<* accountancy branch, and with the commencement oi the contract .for the outiali to Lawyer Head in the beginning of February the first steps were taken to properly establish a- system of engineer's , accounts, arid from the beginning ,of the present financial year (Ist April, 1904) the accounts have, so been kept every detail of expenditure is : .obtainable,-..but to. do this the records must be supplied in the forro die-

tated by the accountant's branch. In the case of the suction well'and'pumping station, the foreman in charge found the work of such a nature that he*oould not well separate out the items in the manner which is required from tie other foremen, and to avoid unduly harassing' hirti; seeing that the work was being pushed'ahead, and he was being continually urged, to ajlow nothing to delay him, I did not insist oh this work being so strictly recorded as the other works of the Board, and as a consequence it has become necessary tq give the returns of the suction well and pumping station combined as one item, which I do as follows: 11. v and m.—Suction Well and Pumping Station Complete. Estimated cost, £20,000. ' Actual cost to date, £14,822 16s Id, which includes about £1,270 paid for duty. The variations already mentioned have meant considerable expansion of the provision for pumps, and as the station now stands it contains three pumps with a maximum dis? charge of at least 6,000 cubic feet a minute. To prevent undue expenditure, instead of Having steam engine, as well as Deisel engine plant for this service, and having four pumps, the station as laid down consists of only two Diesel engines, and three pumps, all three pumps being capable of being worked by the two engines when forced to their guaranteed maximum capacity, but one pump working one engine at three-quarters of its normal power shows practically tho same economy in fuel as when working at its normal power, and when forced to its utmost capacity the loss in fuel economy is not very cons.derable. The following description of this pumping station was prepared a short time ago:— Pumping Station.—At this station three Gwynne centrifugal pumps have been erected. The capacity of each pump has been designed when working under varying loads as follows: First pumping against a head of 26ft, the capacity not to be less than 13£ million gallons per day; and, second, when pumping against a head of 16ft the capacity not to be less, than 18 million gallons per day. The latter condition, of course, could only be maintained during periods of heavy rainfall, and during normal conditions; when the sewage discharge is not expected to exceed 4£ million gallons per day, one pump working for eight hours should suffice. As the work is designed, the periods of pumping would probably be every forenoon for rather more than four hours, and every evening for about three hours. Obviously the deration of pumping will gradually increase with the increase of population, but that would not be until the population had more than doubled, and the water supply had approximated to 7£ million gallons a day, against about 2£ million gallons at present provided, that any alteration would iequire to be made in the present provision. The alteration would then consist of bringing one of the stand-by pumps into daily use, and either duplicating the sewer from Lawyer Head to Bird Island, or else extending the septic tank provisions to sach an extent that all the sewage could be discharged with impunity at the storm water | outlet. For the initial working, the minii mam of septio tank provision has been made, the tank being designed without mechanical appliances beyond such auto- | matic work as will naturally be affected by I the intermittent action of the pumps, and being intended merely to mitigate the nuisance and offensive smells which would otherwise occur at the ordinary starting and continuance of pumping operations. Only one of the two tanks originally designed ha? f.o fa? been erected, and this will only be covered over if the necessity for covering it phould arise. In this connection it should be mentioned that by far the greatest number of septic tanks now being erected in Great Britain are left open. The building at the station is now almost completed, and though the pumps have been erected for somo time, the erection of the Diesel engines has been delayed until the workmen employed on the erection of the build- | ing would have completed all such works as might, by raising dust or otherwise, have proved detrimental to the engines, the workmanship on which is of exceptionally fine : quality. Beside the pump for the tanks is | situated a cellar tank capable of holding sufficient oil fuel for the engines for four or five months, the access to which is external to the building. In this respect, as in the choice of fire-proof hardwood, for the timber work within the engine room, regard has been paid to the necessity for making the station practically fireproof, as obviously any accident which might interrupt the works of the pumping engine would be fraught with most serious consequences. It was with this important fact in view that the pumps and engines were got triplicate and duplicate respectively, arid the pumping mains wero so designed that in case of a breakdown of cither engine, or any one of the pumps, it could; be cut off and the ordinary sewage pumping continued by the other engine. Another matter which has been provided for in the pumping station is that the third pump can either be beltdriven by using an intermediate shaft from one of the existing engines, or can' be driven by a 100 horse-power electro motor; and in the event of electric power being available at a reasonable cost this latter would naturally be erected. It must, however, be remembered that so important a matter as sewer pumping should not be left to be dependent entirely on electric pumping, and consequently no matter how cheap electric power may eventually be, it will always be necessary to maintain the Diesel engines in working order, as a stand-by provision. At the same time, it i 3 very unlikely that for such a service as the storm water pumping electric power will ever be supplied as economically as the Diesel engine service, consequently what is likely to happen if electric power should be provided for the continuous servicei at a cheaper rate than the cost of oil for the Diesel engines is that tho ordinary sewage pumping would be effected electrically, while the storm water pumping, which is expected to happen, say, three or four times a month, and have a duration of probably about 100 hours altogether in the year, would be entirely coped with by the Diesel engines. In connection with the storm water ing,' the total provision when all three engines are working at full capacity should exceed 54 million gallons a day, and, as has been explained elsewhere, when a full system of detritus tanks is provided in the harbor, the storm waiter can be allowed to entirely overflow through tnese tanks, and the main sewer can be used for sewage only. It is worthy of note that the capacity for pumping—namely, 54 million gallons a day, is equal to the capacity of all the six pumps at present erected, ih the Melbourne main pumping station, and that these pumps easily cope with all the sewage flowing from,a population of 350,000 people, already connected to the sewers spread over an area of more than double the total, area that could possibly drain to this pumping station. This fact should show in a convincing manner how sufficient is the provision of the present works for any probable expansion in the population of the district. Another fact which will show that while making such ample provision the present restricted means at the Board's disposal have yet been carefully studied, is that tho Melbou'rne pumps' and engines alone cost upwards of £72,000; while the expenditure for the same thing here is not likely to exceed one-tenth, of this amount. The chief reason for this difference is that owjng to the great depth of the Melbourne sewers, and the distance the sewage has to be discharged, the head against which the pumps work is five times as great as here. Here, owing to the adoption of high speed centrifugal pumps, and; the Diesel engines;, the relative first cost is much cheaper than in Melbourne, and the estimated annual cost is also much cheaper, so that there can be little doubt that five gallons will be pumped here for a less expenditure than one gallon can. be pumped in Melbourne. Melbourne is" specially chosen for this comparison as having the ..premier sewerage system in these colonies. Architecture of Pumping Station.—Whilst it is most desirable that sO important and costly works should not only be protected by a suit-able building _calculated to prevent any danger occurring to the machinery and providing sufficiently attractive quarters to ensure the comfort of those whose duty demands their being continually on the premises, it is also seemly that such a building, should have an atcliitectural exterior 'which' adequately 6xpresse4" its character, and is in keeping with the stability and magnitude of the works which it represerfts." For this purpose, classic architect L ture is most suited. However the only

part of this building where anything is spent for ornament is hi the portico which hides the dwelling rooms from general view.

—lV.—Outfall. ' Estimated cost £33,255. Actual expenditure to dale £20,622 lis 7d. Roughly speaking, this expenditure includes over £3,01W spent on tunnel work tor continuing the sewerage to the Bird Island outlet, and material worked up and ready to be used .in the Bird' Island aerial tramway. And, iii addition' to this, upwards of £2,000 worth of material has been salvaged and is available for use on further work. Ninetyfive per cent, of this material was timber which, having been drawn from excavations and otherwise used, will be sold to various other contracts, or disposed of by auction, so that in oho way or another probably credits to the extent of £1,200 or £1,300 have yet to be recorded to the favor of theso works. The following are the items which have made up this expenditure.-

1. Rising Mains.—These have been increased to 36in in diameter. The estimated cost was in the first instance £3,690, and on tho same basis, adding 25 per cent, for the increase in capacity, this estimate would be amended to' £4,612 10s. Th actual cost stands in tho books at £5,07 18a Id, but instead' of having exceeded, th estimate, as would naturally be iriferrc from this, the work has been, carried oi; well within tVe estimated rate, since n\ wards of £9OO worth of tho timber whie is on hand baa been charged to this cor tract, and will be credited to ib so soon n. other jobs are ready to absorb it. In con itection wdth this part of the work; it woul probably be noticed thai whereas on the plans and the descriptions of work the intention was to use two rising mains, and it was specified "that they will be of wocd or reinforced concrete, according to the situation," yet the estimated price supplied in the schedule was for one cast-iron pipe; the reason of this being, as wag explained at the time, that the wooden pipes strengthened with concrete and steel hoops, which have since been actually put in, would only bo used as a substitute for the single cast-iron pipe if it were found that they could bo constructed for the same money. The average cost of timber supplied' for the rising main was well within the estimate, and hence the work was undertaken in this manner. And with the exception of the valves and pump connection?) the whole of these rising mains from the pumping' station to Tahuna Park are constructed as follows:—The rising main for" sewage, which will continually be wetted, is made of Jarrah staves 4in x 2in, planed on the hwer side and at the joints, caulked with onknra, pitched over with best quality asphalt and pitch, and surrounded with felt, hooped together with bands of wrought iron, and covered with 5 to 1 concrete. The rising main for storm water is constructed of ironbark, and treated in the same manner, and laid side by side with the sewage rising main. Valves are provided so that in case of emergency sewage may be diverted from the Jarrah riring main into the ironbark rising- main. The mains being in duplicate, should it at any time be found necessary to replace either, the ordinary sewage pumping can be entirely passed through the other. The reason why the duplicate mains were provided for timber, and a similar precaution was rot- made in case the iron sirisrle main should prove cheaper, was not because it was anticipated that the timber would have a shorter life than the iron, but because the use of timber in the design of the structure has fewer precedents, and to a certain extent, as compared with the use of iron, may be recorded as novel, and therefore more likely to give rise to unforeseen contingencies. With reference to the relative estimated life of the two materials, it is not likely that cast iron mains, used with so corrosive a material as sewage, would have a life of more than about fifty years. And this is the life which is estimated for the more permanent parts of the pumps and engines. There is ample evidence that ironbark has a longer life than this, and there is good reason to expect that both ironbark and jarrah will prove as durable as oak or elm, both of which materials have stood in similar situations for centuries. In default of better knowledge of timber, experts usually estimate its probable durability from regard to its weight. The weight of jarrah is about 3 or 4 per cent, less than the weight of English oak, while the weight of ironbark is 10 per cent, greater than that of English oak. 2. Gravitation to Storm Discharge and (3) Gravitatipn to. Tunnel.—The latter of these was to carry sewage, and owing to the increase in the provision now being made by doing away with the septic tank proposals in the hill suburbs, it was' possible to construct it of such a size that it could be carried economically as a second storey built up on top of the storm water discharge, and thus, by making one structure to carry both drains, a considerable economy in design was effected. Owing to this,_ the increase in estimated cost of this portion of the work was less than would otherwise 'have been anticipated, and, against the original estimate of £B,OIO, the amended estimate is £3,742 10s, and the amended estimate for the completion of the work from the turn-off at Lawyer Head to Bird Island is now on the workfc as designed less than £19,000, of which more than £3,000 has already been spent. (The estimate given in the schedule which accompanied the report on the sewaee disposal published in the Press on the 29th of October, 1904, showed an expense of £14,960, as estimated for comparative purposes from a certain point called the point of deviation, but this point was about half a mile beyond Tomahawk Head, and consequently this estimate did not include the cost of completing the tunnel work, nor that portion of tfie outfall sewer along the Tomahawk road, whichi would be common to all of the schemes which -were being reviewed in that report.) This work was constructed in the following manner:—The storm water channel was made 6f concrete with the XJ shaped section, which was covered by a Monier slab, and on top of this was carried the sewer of similar U-shaped section, but shallower. This gave the level of the storm water 4ft 6in lower than the level of the sewer, and the gradient being sft in the mile, it was so designed that the discharge of both should beat about the same level, rather more than 2ft above high-water mark. Clearly, therefore, the design pnv vided for the sewer outlet to bo a mile and a-half further away than' the storm water outlet. Should, however, the sewer outlet have to be carried to Tomahawk Head, the level at which it will discharge into the sea .will be proportionately lower, and it is hardly possible that at so low a level an outlet could be effected satisfactorily unless it were submerged. The concrete used was exceptionally strong, being constructed ' of one part cement, two parts of coarse Tomahawk sand, obtained from th'e Board's own pits, and three parts of clean quarry screenings, larger stones feeing only use'd in' bulk work. The location of the sewer was carefully chosen after trial holes had been sunk and a larse number'of bores put down, the chief point kept in view bftirig to so" locate it as lb. avqif any probability of its.being damaged by the. encroachment' from She ocean; consequently, in places the 'cover was so great that; though the formation •was running sandy it was found cheaper: to tunnel than to put'it in by int.

Through Lawyer Head the formation wsentirely volcanic rock, exception of 100 ft, where, owing to the shelving nature of the rock, sand was encountered. To prevent any errosion of this sand by the action of the waves, a concrete breastwall was sunk at the foot of the sandhills, about 100 ft distant. The chief novelties in design for this part of the sewer and drain were the use of Monier covers and the U-shaped section. The reason why. the U-shaped section could be used here, while in the main sewers V-shaped and circular sections are adopted, was that owing to the Gwynne's punips supplying the discharge the sewage is sure to be very fluent, and the factor which would cause trouble in main sewers—namely, long-continued periods without a full discharge : —cannot occur here, where the discharge every time the pumps work will naturally be uniform, and sufficient to give the best cleansing velocity. 4. Tunnel.—The tunnel-work is, as elsewhere described, almost completed, but the sewer portion has not been concreted. With the exception of a short distance through the sand, it will only be necessary to line the invert, the roof and sides above the ;rater-level being sufficiently stable. The otal outlay recorded against this contract s £12,914 7s 2d, which includes plant, etc., I 'cr the next contract.

5. Gravitation from Tunnel to Beach.— fhis work has been commenced, arid over "00ft of tunnel has been driven towards it. luch of the plant being on the ground, it m be started afresh so soon as the Board .we definitely decided the outfall question. 'he balance of the works in conneption villi this are held in abeyance, but in the meantime the work for 'the discharge of torm. water at Lawyer, Head is completed, ;o that the pumps will be able to discharge o soon as they are finished. The total outlay recorded against this contract is £1,035 6s 4d.

—V.—Gtversham Intercepting Sewer.— This work was completed about the beginning of May last. Owing, however, to some disputes between the contractors and bodies and persons claiming against them, the final payments have not yet been made. In the meantime, out of the £7,150 set apart for this work, the total disbursements by the Board have been £6.418 14s Bd, and the unexpended balance will more than suffice to meet all possible claims and, if necessary, the threatened legal proceedings. The design of- this drain is similar to the U-shaped drain described above for the ocean outfall. This section is justified from the fact that it is not intended to carry any sewage. When the sewers are completed throughout the area which it serves it will act as a storm-water, overflow for these sewers. Since its completion rain has fallen on more than one occasion in excess of the quarter-inch per hour for which it has been designed, and the discharge proved sufficient. Consequently, when the sewers are completed, which will themselves carry a rainfall equivalent lo nearly 2in in twenty-four hours, the combined sewers and drains will be sufficient, with any normal storms, to prevent any overflow on to the Flat; and if any such should occur, the volume of would not be sufficient to do. any material damage, since waterspouts arid heavy • thunderstorms are of short duration.

—Vl.—Frederick Street Works.—

The original estimates for these •works were that the detritus task and the sewer works would each be of about equal value. What has actually happened is that the sower work has been carried out for a considerably less sum thai the estimate, whereas the. detritus tank has cost a con T siderable sum in excess of the estimate. So different is the formation through which the tank was sunk from the estimate that the contractor was compensated for having his contract cancelled; and what was expected to be broken rock was found to be gravel, with some treacherous veins of running sand. The total depth that these tanks-were sunk to was 53ft beneath the established level of the street, and for upwards of 35ft the excavation was through this very treacherous ground. In addition to the extra expense which naturally resulted, there was a great deal of inconvenience, and consequently extra expenso, owing to the Harbor Board reclamation having, during the long period while the contractor was delaying arid being delayed on the sewer part of the work, extended beyond the stage that was anticipated. It is satisfactory, however, that the total cost of these works has been £5,287 12s 4d; against £5,000 estimated, and when the contribution of the Harbor Board is deducted the loan estimate shows a balance in favor of the Board of £312 7s Bd. The estimated cost of cleaning out the detritus tanks was 3s. Up to date it has never exceeded .this figure, and the fortnightly cleaning at present adopted proves sufficient.

—VII. and "Viii.—Branch Sewers, etc.— As has already been explained, the septic tanks proposal provided for in VEL is being abandoned, and the expenditure of branch sewers will be increased in proportion. Hence the total estirriate for branch sewers may be taken as the total of these items—that is to say, £44,100. The details have now been worked out for all these branch sewers that are at all likely to be carried out within the next thirty years, and aggregate £45,700. Of this expenditure the o*rgill roaH sewer has absorbed £1,403 18s 9d. The first section of this—namely, the part in Caledonian .road—should be completed next week. The estimate for this part of the work was £2,245. Though greater difficulties were experienced, owing to some unrecorded culverts having brought the tide in en to the work, it is yet expected that this estimate will not be much exceeded, and there is little doubt but that as the workmen get accustomed to the class of work the present rate of cost will bo diminished, and there is every reason to believe that the estimates nowmade will be realised.

—lX.—Main Arterial Drains Across Flat.—• _ Estimate, £.2,500. Of this work the Kensington main outfall sewer has been constructed at a cost of £1,258 17s 9d, against an ■ estimate of £I,OBO. The extra expense was. almost entirely due to- the cost of lowering the gas mains, an item which was not known of when the original estimate was run out. —X.—'Fresh Reticulation. Estimate, £23,600 About one-sixth of this wort is completed—viz., & miles out of forty-two. The average price of all pipe work has proved considerably above the estimate, owing, to the price of New Zealand pipes being considerably greater, especially for the small sizes, and pipes of similar quality on which the estimates were made. The total expenditure under this.head and in the pipe' Kites'' which have been laid for the branch sewers has been £10,167 i\s 6d, against an estimated cost for the fame work of £7,781 Bs} showing a loss mader , this head of £2,386 3s Bd, as compared' with estimates. . '