THE CITY WATER SUPPLY.
REPORT OF THE CONSULTING ENGINEERS.
WAINUI—A NEW DAM AND SECOND MAIN.
IMPROVED RETICULATION IN THE CITY.
PROPOSED EXPENDITURE OF £230,000.
A special meeting of the City Council was held last evening to consider the report of the Water-supply Committee covering the report of Messrs. Ferguson and Mestayer on the whole question of the water-supply. The Committee’s recommendations were as follows:—
- That Messrs. Ferguson and Mestayer’s report be adopted, with the inclusion in the scheme there recommended of the dam at Karori proposed by the City Engineer, and that the necessary proceedings be forthwith taken to obtain the consent of the ratepayers to the raising of a loan to enable the scheme to be carried out.
- That, in accordance with clause 258 of the Municipal Corporations Act, 1900, three months’ notice be given to all persons who use water for motive-power, other than for lifts, of the Council’s intention to cut off such supply until the scheme is completed, such notice to date from the 1st February next.”
THE WORK AND THE BILL.
In their report the engineers, Messrs. Ferguson and Mestayer, do not oppose the erection of a dam or reservoir at Karori, but think it should be deferred. To sum up, they recommend—
(1) the erection of a storage dam or reservoir at Wainui;
(2) a new main from Wainui to the City boundary, with tunnels, new bridges, bridge-widening, wayleaves, etc.;
(3) new mains in the City, with deviations and replacement of sewers, drains, gas, water-pipes, etc.;
(4) appliances for straining the water for filtration purposes;
(5) purchase of land included in the Karori catchment area.
And their estimate of cost, which excludes the Karori dam, is £230,000.
DETAILS OF THE REPORT.
The first half of the engineers’ report traverses seriatim the recommendations of the City Engineer in his report of 10th July, 1901. In the main they support his views, with, of course, the essential difference that they consider the construction of the Karori reservoir should be deferred.
They clearly state that they have arrived at the conclusion that it is chiefly to Wainui that the City must look for the supply of water, the Karori supply being reserved solely for those high levels which cannot be reached by the mains from Wainui. And they remark:—
“We recognise that Wellington has in its two waterworks obtained control of the best sources of supply in the district, and that the suburban districts must be more satisfactorily served by co-operation with the City of Wellington than in any other manner. We, however, consider that so soon as the demand for supplying these suburban areas arises, it will be absolutely necessary to construct a further reservoir or reservoirs at Karori of sufficient capacity to conserve as far as possible the water from that watershed.”
KARORI WATERSHED AND THE HIGH LEVELS.
The engineers emphasise in the strongest possible manner the recommendation that the catchment area of the Karori stream should be acquired without delay by the Council; that the area so acquired should extend about a chain in width over the ridge of the watershed, and should be fenced in a thoroughly substantial manner on that boundary.
The whole of the area of the watershed should be thoroughly cleansed, and planted with suitable trees and shrubs. At the present time this area is used as a dairy farm and sheep run, and is in an exceedingly dirty condition, and such as should not obtain in any watershed supplying water for domestic purposes.
But if it was cleansed and planted, and the water strained before entrance to the pipe service, they think that no exception could be taken to its quality, which opinion is based upon personal observation as well as upon the result of bacteriological and chemical analysis carried out by the officers of the Department of Health.
The result of planting would be to conserve the rainfall, thus enabling a larger portion thereof to be retained, a point of great importance in view of the small area available, its height, and its proximity to the high level districts.
THE POINT OF DIFFERENCE.
With reference to the proposal of the City Engineer to construct an additional dam at Karori, the engineers support its construction when the high level consumers demand it. They find that the existing reservoir only contains when full some 45,000,000 gallons, and are of opinion that owing to the altitude of the basin and its proximity to the City, as much water as possible should be conserved from this area, in order to serve the high level districts without the necessity for pumping.
This is more especially desirable having regard to prospective demands which may be made for the supply of water to the high level areas adjacent to the City. When such demands are conceded it will be absolutely necessary that the proposed dam should be constructed, and considering the area of the watershed and the rainfall thereon, they are of opinion that a total provision should then be made for impounding not less than 100,000,000 gallons.
“The volume of water which can be obtained from the present watershed being only sufficient to afford a regular supply of 60 gallons per head per day to a population of about 11,000 in dry seasons, we consider that it should be reserved for the present supply of the high level districts generally; and after an additional supply is brought in from Wainui-o-mata (as hereinafter recommended), that it will be necessary to restrict the Karori supply to the service of those of the high level districts on the north and west sides of the City—being those immediately adjacent to the supply—and ultimately (if water is required for the adjacent high level suburban areas) to the higher levels in those districts only, leaving the lower portions thereof to be served from the Wainui supply, as well as the high level districts on the east and south sides of the City.
“In order to afford the residents in the high level districts a satisfactory supply, it will be necessary to lay as soon as possible certain additional mains of increased capacity, and we are of opinion that these mains can be so arranged as to form part of the permanent system recommended by us, and without any loss being occasioned by the transference at any time hereafter of any one or more of such districts from one source of supply to the other.
“We find that the gathering-ground supplying the present reservoir is only 611 acres, but being informed that a tributary of the South Karori stream could, by works of small cost, be intercepted and led into the existing watershed, the City Engineer has, at our request, had a survey made of the gathering-ground of this tributary, which was found to contain only 150 acres, of which not more than 100 acres could be made available, thus making the total catchment area about 711 acres. We think that for so small an additional area the cost of the necessary works and of the purchase, planting, etc., of this land would not be warranted at present.”
WAINUI FOR STORAGE SUPPLY.
Having arrived at the conclusion that Karori must be looked to for the high levels, and Wainui for the bulk supply, the engineers proceed to deal with the latter. They find that the present reservoir at Wainui is of little value for storage purposes owing to its limited capacity (about 20 million gallons when the draw-off is lowered by works now being carried out by the City Engineer), though it is to a certain extent useful as a settling pond.
“Having regard to the certain future growth of the City, which we assume will before many years have a population of 75,000 inhabitants (this number being also the population upon which the drainage scheme was designed and executed), we consider it essential that the fullest advantage should be taken of the facilities which exist at Wainui for the conservation of a further supply, more especially as owing to the narrow configuration of the valley, the generally rapid rise of the ground therein, and the absence of any wide expanse of comparatively level areas, the Karori basin is distinctly unsuitable for the economical construction of storage reservoirs of large capacity; whilst the smallness of the gathering ground, and the low rainfall thereon as compared with that at Wainui (it being little more than one-half that of the latter) render the Karori watershed incapable of supplying a population of rather less than 13,000, even if the outside area of 100 acres hereinbefore referred to be added thereto.
“At Wainui, on the other hand, the area of the present gathering ground is about 7000 acres (without considering the question of the inclusion of the Orongorongo watershed, of which we have no personal knowledge), and this, with adequate storage, for which the watershed presents every facility, will easily provide for a population of more than 140,000.
“We are informed that the lowest dry weather flow of the Wainui stream observed since the installation of the works has not fallen below three million gallons per diem. On a population of 75,000 inhabitants, after allowing for the water available from the Karori watershed, there will be required for domestic and other purposes fully four million gallons per diem, and therefore in dry seasons the storage capacity of the reservoirs at Wainui will be trenched upon to an extent of about one million gallons per diem.
“We are of opinion that storage capacity should be provided for not less than 110 days’ supply, which at a draught of one million gallons per diem from the reservoirs in addition to the estimated minimum flow of the stream will necessitate the construction of a new reservoir having an available storage capacity of ninety million gallons, as the present reservoir will have a capacity of twenty million gallons when the works now in progress are completed. We recommend that, in order to be certain that this shall be impounded, and a sufficient allowance be made for evaporation, the dam proposed by the City Engineer shall be raised two feet higher, and strengthened proportionately.”
THE NEW WAINUI MAIN.
The City Engineer’s recommendation to bring in a new main from Wainui is adopted, the Engineers being of opinion that although Karori can for the present supply the high levels, a further supply should be obtained. The new Wainui main should be reticulated so as to conserve its pressure for the South Wellington districts and the greater part of the high level districts of the City.
“We therefore recommend:—
“That steps should be taken to obtain powers from the citizens to lay a main commencing 30in in diameter at the reservoir at Wainui, and continuing that size to the City side of a new tunnel to be driven through the hill above the Waiwetu River.
“That from this point to Taranaki-street (at Courtenay-place) there should be laid a main 24in in diameter.
“That a 20in diameter main should be laid up Taranaki-street and Wallace-street as far as Bidwell-street.
“That the main should then be reduced to 18in diameter and carried down to the junction of Revans-street and Adelaide-road, and there connected with the existing 12in main in Revans-street.
“That a 14in main should be laid up Adelaide-road as far as its highest point, continuing through to Berhampore with 12in, 10in, and 8in pipes.
“That from the 14in main at Stokes-street an 8in branch be taken to the highest point of Constable-street, and that a 12in main should be laid along Webb-street from the present Karori service in Wordsworth-street to connect with the proposed main in Taranaki-street for the purposes—of affording a better supply to South Wellington until the new supply from Wainui is available; of providing for an alternative supply to that district from Karori in the event of any accident with the 24in main; and of supplying the high level district south of Webb-street from Wainui so soon as the demand on the Karori supply renders this course advisable.
“To serve the districts on the slope of Mount Victoria, we recommend that from the junction of the proposed 24in and 20in mains at Taranaki-street there should be laid a 10in main along Courtenay-place and up Majoribanks-street to Austin-street. Such a main will be sufficient for the future supply of the Roseneath district.
“We recommend that at various suitable places along the line of route cross-connections with valves be made between the present and the proposed new mains. By this arrangement, in the event of a breakdown in either of the mains, the supply of the City would be temporarily continued through the other main.”
Figures are quoted to shew that though the present Karori and Wainui mains have sufficient capacity to deliver into the City 11,000,000 gallons daily, the terminal pressure would be too low for the City’s protection without recourse to pumping. “Having therefore in view the prospective increase in population we elect, in preference to the installation of pumping plant and service reservoirs, to recommend the more permanent and economical alternative of a duplicate main from Wainui. We believe that financially it will be cheaper to avoid a complicated system of pumping and reservoirs, and that the duplicate line of pipes will safeguard the City against any possible breakdown in either main.”
WASTE IN THE CITY.
Facts and figures are quoted to shew that the normal average consumption in Wellington, for domestic purposes and waste, is not less than 125 gallons a head a day. Two-fifths of the amount, or 50 gallons a head per day, would be a liberal and ample supply. The flow into the City during the slack hours of night (at which time the water must for the most part be wasted or improperly used) amounts to nearly seven-tenths of the quantity flowing in during the busiest portion of the day. This waste disadvantages the high levels and increases the amount of sewage-pumping that must be done.
Recommendations:—Venturi meters should be installed on the main from Wainui (already decided on); on the main from Karori; and on the Wainui main at the City’s northern boundary; and all water taken from the main between Wainui and the City should be metered, so that a balance may from time to time be struck with a view of checking any waste or leakage on the long length of main between the reservoirs at Wainui and the City. In order that the City may be subdivided into suitable areas for the purpose of localising waste or leakage, and of ascertaining the true and relative consumption in such areas, the Engineers are strongly of opinion that on new mains or sub-mains laid within the City, and when existing mains are altered or re-laid, provision should be made at suitable places by means of bye-passes and valves for the insertion of portable test meters.
They endorse the recommendation made by the City Engineer that meters should be used in connexion with the supply of water to hotels and gardens, and have embodied provisions for this purpose in an amended and consolidated by-law, which it is proposed to enforce rigorously. They consider that where water is used for such purposes there is much greater probability of excessive consumption and waste than in the case of a purely domestic service.
The present Inspector of water fittings would have to visit thirty buildings in a day if each one in the City is to be visited once a year. Each should be visited thrice annually, and one man cannot do it. They strongly recommend that until the leakage is materially reduced, an Inspector should be on duty during at least eight hours every night, as detection of leakage by sound is then much more easily effected; and that there should be for the present at least three Inspectors to efficiently carry on this work. But they do not go to the length of advocating the metering of all supplies.
The report states:—“With reference to the general question of metering all services we are of opinion that it is not desirable at the present time to compel the provision of meters except in cases such as those indicated in the proposed by-law; because we consider that it is not advisable to unduly restrict the supply of water for domestic purposes generally, more especially in the poorer districts, and payment for water by meter would probably have the direct effect of reducing the consumption in such districts below that which is advisable from a sanitary standpoint. The measures we have advocated for the reduction of waste should, if properly carried out, be sufficient without incurring the large capital and annual expenditure which a universal meter system would require.”
MISCELLANEOUS.
Where pressure has fallen off owing to reduction in inside area in pipes resulting from accumulation of silt, the pipes should be cleaned or replaced; and in no case should a pipe of 3in diameter be re-laid where more than one fire-plug is connected therewith. The laying of larger pipes will improve the pressure in many places; but the number not being known, these replacements are not provided for in the estimate. In future no main less than 4in should be laid except for domestic supply to a very few houses only. Connections should be made at closer intervals than at present between different-sized mains in the same street. All alterations in principal streets should be effected before the wood-paving is laid.
Filtration through sand or gravel is undesirable at Wainui and Karori, and would cause loss of head; a simple form of mechanical straining should be sufficient for each supply, and £7000 is placed on the estimate for this purpose.
The cost of cleaning and stopping the leakage (possibly dangerous) in the present Wainui reservoir should be met out of maintenance as soon as the new reservoir there is completed; and when the second Wainui supply is brought in, Karori reservoir should be cleaned and altered (also out of maintenance) to allow the water to be drawn off at a higher level.
Increased pressure on the main line of pipes on the Hutt-road would result from the replacing of the water-race by 3in pipes at a lower level, and from the proposed new works. This increased pressure may lead to a few failures in the Hutt-road pipes, the original pipes being lighter than those now recommended.
The City Engineer’s estimates, though increased in one or two cases, are generally confirmed as accurate. The allowance for pipes, the biggest item, is based on current market quotations (which fluctuate), and on the assumption of immediate execution of the work.
The report concludes:—“We are of opinion that in the case of the concrete dam at Wainui, where unforeseen difficulties may arise both in connexion with the foundation and from sudden floodings of the river, the work had best be carried out by day labour, or by small contracts. Similarly we are of opinion that the laying and jointing of mains should be executed by the Council’s own employees, and our estimate has been framed on assumption that this course will be adopted.”
THE VIEWS OF COUNCILLORS.
In moving the adoption of the report, Councillor Devine said it was a matter for congratulation that Messrs. Ferguson and Mestayer had borne out the advice of the City Engineer, given in his report of July of last year. Continuing, Councillor Devine urged that the acquisition of the enlarged catchment area at Karori was essential, partly on account of the restricted area at present owned by the Council, and partly on account of the surrounding land being heavily stocked with cattle. As to the Karori reservoir, he pointed out that they had always been led to believe that it was capable of holding 90,000,000 gallons, whereas it only held about 45,000,000 gallons; and he urged that the construction of an additional dam, which would cost about £45,000, and ensure a good supply to the high levels, would render the proposals as a whole far more acceptable to the general body of the ratepayers than an incomplete scheme would be, and tend to defeat the adverse votes of those ratepayers who already had a sufficient supply, and were not inclined to consider other people’s requirements.
Councillor Smith, in seconding the adoption of the report, thought it was a serious omission that the Engineers had not recommended the construction of an additional dam at Karori. The extra cost of such a work would not be so great in proportion to the whole cost as was at first imagined, and he urged that every care should be taken to provide a thoroughly sufficient reserve supply for the higher levels. The public should be informed that without this additional area, the supply for the higher levels would not be so complete as it would otherwise be.
Councillor Luke complimented the City Engineer on his report being practically adopted by Messrs. Ferguson and Mestayer, who were the two most competent men to report on the matter. He considered that the ratepayers would be only too glad to vote the money for the acquisition of an additional catchment area at Karori. He did not agree with water meters being put on to private houses. Further, the Engineers practically bore out his contention that the pipes from Wainui were not of sufficient thickness, and there was an absolute necessity, he urged, for the duplication of that main. He did not agree with the proposal for an additional dam at Karori, which would cost about £50,000, and might lead to the defeat of the whole scheme. Only seven gallons per head per day were being given for other than domestic services out of a total daily supply from Wainui of 116 gallons per head, and he did not agree with the proposal to do away with the supply of water for lifts and so on. The higher levels generally would get a sufficient supply under the proposals without going to the additional expense at Karori which was suggested.
Councillor Tolhurst urged that a large part of the increase might be saved if the City were fully metered.
The City Engineer, in answer to Councillor Izard, said it had been ascertained by careful calculation that only three-tenths more water was used in the busiest part of the day than was used at night—that, in fact, there was a waste of seven-tenths.
Councillor Izard said it seemed incredible.
The City Engineer said the calculations were based on formulae which had been proved correct over and over again.
Councillor Tolhurst thought that before voting an expenditure of £230,000 they should consider whether it would not be wiser to conserve the water we already had. When the Wainui scheme was equipped it was estimated it would be sufficient for a population of 75,000 people. The Council might consider whether it was not now really sufficient, except for the higher levels, the daily consumption being now 125 gallons per head, while 60 gallons was considered to be quite an adequate supply. The Council must remember that under the Municipal Corporations Act the Water Inspector had no power of entry after sunset.
