CHRISTCHURCH WATER SUPPLY.

Globe, Volume XXI, Issue 1810, 9 December 1879, Page 3

CHRISTCHURCH WATER SUPPLY.

The following is Mr Hubbard's report on tho Water Supply, presented to the City Council last night:— " Hereford street Chambors, Heroford street, " Christchurch, December Ist, 1870. "His Worship the Mayor and Members City Council, Christchurch. "Gentlemen, — In accordance with instructions received to examine the proposed source of Bupply at the Waimakariri, distant 18 miles from Christchurch, at an elevation of 400 ft above Cathedral squire, and to furnish you with my opinion upon the same ; also, a reliable estimate of the cost of providing an effectual water supply for Christchurch therefrom, presuming the city to contain 50,000 inhabitants, I have now the honor to lay before you my report. Before entering upon matters connected with the source of supply in question, I wish to call your attention to certain acknowledged conditions which should be considered when adopting a source of supply for a city or town, and then to apply each of those conditions to the scheme under consideration. The conditions which influence tho selection of a source of wafer for the supply of a city or town are—- " 1. The quantity to be provided. "2. The quality of tho water. " 3. The greater or less facilities for tho economical extension of the works as a matter of construction. "4. The avoiding, if possible, of mill streams, as the compensation to be paid to mill owners may involve a large expenditure, particularly where a millowner has power to impound the water. " 5, Whether the supply should be constant or intermittent. "6. The relation between the immediate and the prospective financial conditions of the undertaking. " Application op Ist Condition to Proposed Scheme pob Chbistchtj-bch. " Quantity to be provided. " Of the gross population, it is not always that the whole will take water, the proportion of non-consumers to consumers will depend upon many circumstances—facilities for independent private supplies end the position of the promoters of a scheme with regard to the town, that is—whether they are a simple trading company or the local authority itself, legally competent to make by-laws concerning the use of water, and to levy general rateß for the same. With regard to the former circumstance, Christchurch is at present, but with few exceptions in the north and northwest Jquarters, adeqrately supplied with water for domestic consumption by artesian tube wells, generally ljin. diameter, driven to depths of from 80ft. to 90ft. down, to what is popularly known as the first stratum of water, when it rises to a few feet above the surface, it has, however, to be pumped or carried to upper floors of buildings for use, for extinguishing fires, and all other purposes where pressure is required. Each individual householder can obtain a supply at a cost of from £4 to £B, according to circumstances. It is now also an established fact that a second stratum of water exists at a depth of nearly 200 ft, but the great cost incurred in driving pipes to tho depth renders it prohibitive to the generality of private individuals. Notwithstanding the above facts, it is very evident to me at least, from extensive observations made during the past fivo years, that the wells are rapidly and signally failing, and that to a very sorious extent, the flows obtained from wella sunk now being very indifferent to those of five years since. If the City Council possessed the power to control the great waste now taking place, I have no doubt that, in time, the pressure would materially improve, but, as this power can scarcely be hoped for, and as the number of wells increase, and tho great waste continues, I fear it will not be many years before the water will fail to rise to the surface, and that for aomo considerable time (until the pressure be restored) tho inhabitants will then bo at Bcrious inconvenience, if no other source of supply be obtainable. With regard to tho position of tho promoters of a scheme. Tho proposed supply being in the hands of the local authorities, competent to levy a general rate, it is reasonable to expect that at least all new houses will take the supply offered by the proposed scheme, with the advantages of high pressure. Therefore, under the circumstances, I am of opinion that it could not be deemed wise to lay out a system of waterworks for Christchurch without a viow to the wholo population being ultimately included amongst the consumers. The natural base of an estimate of the required quantity is the population of the district, which we will suppose is known with sufficient accuracy for the purpose. Guided by carefully assumed or observed rates of increase, it will be necessary in most cases to calculate upon the probable population of some years hence. I propose in this case, however, to sioiply support the views of the Council in fixing the extent of the proposed scheme to a supply for Christchurch as being likely to contain 50,000 inhabitants, based upon the following calculation, that the City of Chrißtchurch contains an area of 1079 acres within the portion east of tho domain as colored on tho accompanying plan. It is ÜBual to allow 47 people por acre in towns, thereforo 1079 acres multiplied by 47 gives a population of 50,713. It will be seen that the Council has not over-estimated the future possible and probable population upon tho area proposed to be supplied, and upon which all my calculations are based. I am also of opinion that it would be very unwise to provide a scheme for any less number of people, especially from the source of supply under consideration, owing to its distance from Christchurch in necessitating an expensive conduit which can be laid at first, to meet the demands of the future population sit a far less cost than two separate conduits of small dimensions, tho second of which to bo laid when required for extension. In calculating the quantity to be provided for dorrc-stic consumption and trade purposes, &e., I have estimated at 20 gallons por head por day for 50,000 people, which to some may appear a low estimate, but which I can from experience prove is *uffieiont for all purposes, provided proper steps bo taken for the prevention of waste. The consumption at the present timo in Liverpool, a watercloset town containing 672,000 people on the constant system, where the same measures are taken to prevent wasto as I recommend to be adopted for Christchurch, is now only 14 gallons per head per day for domestic purposes, including all wasto, and 7 gallons per head per day for trade purposes, making a total of 21 gallons per head ; it must bo remembered also that Liverpool is a largo manufacturing town, which requires as much as 7 gallons per head per day for this purpose. Carlisle, another watercloset city, requires only 20 gallons per head per day. Canterbury, also a watercloset city, requires only

18 gallons per head, and many others are known to me whore the consumption for all purposes does not exceed 20 gallons per head pbr day. In addition to the übovo I recommend an independent fire-extinction service at all times in reserve, capable of throwing jets varying in height from 60ft to 80ft during any time, day or night, whether domestic consumption or for trade purposes is taking place or not, sufficient in quantity for ten jets of 150 gallons each per minuto or a total quantity of 1500 gallonß per minute, making a total quantity as follows : Gallons per day. " For domestic consumption, trade and public purposes for 50,000 inhabitants at 20 gallons per head per day 1,000,000 " As it, has been proved upon several occasions that tho greater portion of tho water is consumed during tho first fivo hours of the day, between 6 and 11 a.m , it is usual to csliniite that ono-hnlf of tho quantity to bo provided must bo capable of delivery during tho above fivo hours a 3 follows : 1,000,000 gallonß in 24 hours 500,000 „ 5 hours 100,000 „ 1 hour 1,666 „ per minuto. " Therefore tho total quantity to bo delivered per minute will be— Gals, per minuto. " For domestic consumption, trade, and public purposes ... ... 1066 "For fire prevention ... ... 1500 "Total 31GG Condition No. 2. (Quality of tho water.) " Tho water proposed to bo supplied to Christchurch from tho source selected is all that could be d»eirod for a potable wator ; it needs no artificial purification, it being naturally filtered in passing through the cleansing media of sand arid gravel stono. A eamplo of tho water has undergono a chemical analyeia at the hands of Professor Bickerton, and proves to be an excellent wator for all purposes. I would, however, recommend, if this schomo be carried out, that tho aetion of this water upon lead and galvanized iron be ascertained, and that experiments bo made as early as possible so as to subject each material to a severe crucial test, in order to determine which will be the better material to adopt for tho house services. " The temperature of this water is 52deg., and would be delivered at this temperature winter and summer alike, as it would enter the main and distributing pipes direct from the underground source, and so reach tho consumers without being exposed to the influence of the atmosphere for one moment, which is a priceless boon, and one which in moat other sources of supply can only be obtained by very expensive arrangements. The water having passed through the cleansing media by percolation, baa been rendered pure and bright and well aerated, and attained the mean temperature of the atmosphere for tho year, and bocomes of admirable quality, characterised—--Ist. By being at all times the normal and useful temperature of 53deg. Fah., or 16 degrees colder in the summer and 16 degrees warmer in the winter than ordinary river water. 2nd. By being clear, colorless, and bright, and not affected by the heaviest rains or the longest drought. 3rd. By being free from living or dead organisms of any kind, and from all organic matter, animal or vegetable. 4. By being well aerated and fresh, and by holding a large proportion of air and oxygen gas in solution, and by being pleasant and refreshing to the taste. The normal temperature of the water being thus maintained, st least in a great degree, when delivered into the houses of the consumers, the distributing pipes are not liable (as with river water) to freezj and to burst in the winter, and the water is at all times pleasant to drink. Condition No. 3. (The greater or less facilities for the economical extension of the works as a matter of construction.) " Of all the conditions named, perhaps the most important is that relating to the facilities for extension for parts of some works, such as wells, reservoirs, filters, pumping machinery, &c, additions may be made with great facility, while others, long conduits for instance, may offer serious or at least considerable difficult ies if useless expenditure is to be avoided. So much is this the case that but very rarely are the several parts of a carefully studied system of waterworks perfectly harmonious at the outset. In this case when the time arrives for a larger supply than 1666 gallons per minute for domestic consumption, the fire prevention quantity remaining constant, there will be no alternative but (o lay down another main, for although a much larger quantity of water could be delivered by the main I recommend to be provided, it could not be delivered without destroying the pressure in reserve for fire extinction purposes. " I do not deem it necessary to provide a main at first of greater capacity than one capablo of delivering the above quantity, as I am of opinion that it will be sufficient to meet the requirements of the city and immediate suburbs, if needed, for the next 20 years. Condition No 4. " (Belating to compensation to millowners, does not apply in this case.) Condition No. 5. " (Should the supply be upon the constant or intermittent system.) " Experience provos that undoubtedly the best system of supply is the constant, and should be adopted wherever possible in the true sense of the word, not by storing the water in cisterns large enough to hold all that the consumer may require in the 24 hours, and then to be resumed, for although this is in one sense a constant supply to the consumer, it is not constant service by the water works, and is open to many serious objections, such as contamination by exposure, and failure to clear the cisterns, loss of freshness, and temperature, &c <f A constant supply is one in which the mains and all other pipes of the waterworks are constantly charged, and the consumer is at all times, day and night, able and at liberty to draw from them water for his legitimate use, " It is not here necessary to enlarge further upon the desirability of a constant supply, or a second thought necessary to establish the superiority of a continuous supply over the house storage system. " Many objections were formerly raised against the constant system owing to the great waste of water taking place, but valuable improvements have of late years been made with regard to the fittings and method of checking waste, which will be described anon when dealing with the question of distribution of the water, and which I recommend to bo adopted. " Condition No. 6. (The relation between the immediate and the prospective financial conditions of the undertaking.) "In this case, where the local authorities will have power to levy a general rate, it will simply resolve itself into what amount will be sufficient to provide for interest and sinking fund on loan. In calculating this, allowance must be made for revenue dorivable from water power for machinery. I am of opinion that, taking into consideration the present population of the city, amounting to 13,000, possessing a very fair domestic consumption supply already, it would bo perfectly safe to recommend that, for the next fifteen years at least (notwithstanding all new houses may take proposed high pressure supply), that a proportion of the domestic supply amounting to one-half of the quantity provided by this scheme, or a 3 much say as 1000 gallons per minute, might be sold for the purpose of driving machinery, which, at a very low estimate p?r horse-power obtained, would produce an income of at least £ISOO per annum. At the same time full provision should be made for all interest whatever that may become duo until revenue is derivable from the works, say fifteen months after they are commenced. Having applied each of the foregoing conditions to the schemo under consideration, I will now proceed to give my opinion upon the source of supply selected by the Council, afterwards as to the method I should recommend for conveying and distribi.t'ng the wator in tho city, and finally as to the total cost of the undertaking. Ist.—Sottbck of Supply. " The source of supply is situated 18 milce, in a north-westerly direction from Christchurch, at an elevation of 400 ft. above the city, on the south bank of the river Waimakariri, whore a trial cylinder, 3 ft. indiametor, has been sunk to a depth of 25ft. into [the shingle and water-bearing Btratum. As you are aware, on Oct. 21st last, the yield of the cylinder was tested, and 400 gallons pumped therefrom in 52 seconds, which equals 664,600 gallons in 24 hours, or 461 gallons per minute. Before pumping, the level of the water stood at sft 3in from the top of the cylinder, and when the pump was throning

the above quantity of 461 gallons per minute, the water level was lowered 4ft in lmin lOsec, or a depth of Oft 3in from top of cylinder, at which level it remained whilst the discharge kept constant. Immediately the pump was stopped, the water again rose almost instantly to its normul level of 6ft 3in from the top of the cylinder. It will be remembered that on the previous occasion of testing the yield of the cylinder, the river was running within a chain or so of it, at which time the water Btood at 3ft 3in from the top. On Oat. 21st, upon the second occasion of testing the yield, the river was found to have shifted its bed to a distance of 15 chuins from the cylinder, and the water level was 2ft lower in it, clearly indicating that the level of the water in the cylinder was influenced by the position of the flow of water in the river bed adjoining, the pressure of the water when running nearer the cylinder would cause the water to rise to a highor level in it than when removed to some distance off, when the line of saturation gradually falling where the river ia flowing, the pressure would be considerably less, thus accounting for the lower level upon the aecond occasion. On October 28th last I again visited the propoEed site for the intake works, also tho surrounding country. I oxaminod tho level of tho water in the cylinder, and found it to be the same as upon Oct. 21st, and the position of the flowing river tho lime. I also tojk th) diff.roice of the level between tho tap water in cylinder and tho water flawing in the river 15 chains distant. I found the water in the cylinder to bo 4 00ft. loner than that of tho river, which, together with tho reasons I have given for the difference of level in the cylinder according to the position of the river, clearly indicates that the source of supply is no other than the water which paturates through tho shinglebed from the flowing river along its course, which is continually flowing underground in tho direction followed by the water flowing on top, or at right angles to the level contours of the surface, spreading only underground upon each bank, owing to the porous nature of tho shingle. There can be no doubt that the quantity required can be obtained, or even a isuch larger quantity when necessary, but before I could offer any opinion as to tho precise number of cylinders, or whether one large cylinder sunk to a greater depth would be sufficient, I should require to make Borne further experiments before preparing any detail for the intake works, to ensure the water remaining at a permanent level in the cylinder, when not only tho quantity required would be passing down the main, but to provide also for a much larger quantity than required, for future extension, the extraction of which larger quantity would have some considerable influence upon the permanent level of the water in the cylinder, which is a matter for very serious consideration, as the main, when fixed, cannot adapt itself to any alteration in the level of the water in the cylinder or other intake works that might be designed. I have, however, allowed a liberal sum in the estimated cost of the works, which, in my opinion, will cover the expense of the necessary works. With regard to the surroundings of the site selected, and the probable shifting of the river, which no doubt it will do every fresh that takes place, I am of opinion that it cannot materially alter its course between the gorge and the site of intake works, as the geological formation remains the same throughout its course, and the topographical features of the district from the gorge up to the site selected are favorable to my opinion. " Proposed Method of Conveying ard Distributing the "Water in Christchurch.—l would recommend the laying of a main pipe from the intake works, past the Miners' Arms, through Courtenay and Biccarton, to the city, a distance of 18 miles, of cast iron socket pipes, 24 internal diameter, of different thickness, to withstand the various pressures due to an average fall, as fellows : Total Fall. From 18 miles to 14£ miles, equal to 3f miles, averaging 28ft per mile, or 75ft From 14J miles to 9J miles, equal to 4$ miles, averaging 29ft per mile, or 120ffc From i)\ miles to 3J miles, equal to 6-} miles, averaging 27ft per mile, or 167 ft From 3J miles to 0 miles, equal to 3J miles, averaging 12'8ft per mile, or 38ft Total—lß miles. 400 ft "I find on reference to Doyne's contour map, that the height at the site selected would be 420 ft above Cathedral square, and the barometrical levels taken by myself show 412 ft. The former, of course, would be the more correct; therefore my calculations, based upon an available head of 400 ft, would ensure satisfactory results in practice. I would recommend pipes with turned and bored joints. They can be laid with greater rapidity and at less cost than can pipes with lead joints. Turned and bored joints require no lead, but joints are simply coated with a thin coat of Portland cement, and one pipe fitted into the other, every second pipe of the larger sizes being used to drive the preceding one close home into the socket, the smaller sizes being driven home with a mall, the special castings and bends to be jointed with lead only. A meter should be fixed at the mouth of the intake with a sluice cock, in order to regulate the quantity to the requirements of tho city as the demand increases. DISTBIBTJTINa PIPES, HYDBANTS, ETC., IN THE OITT. " I have calculated the necessary diameters of pipes to be laid in each street, so as to secure the number of fire jets at various places as indicated upon the accompanying plan, which Bhows the boundary line up to which 10.80 ft. jets could be obtainable, all within the part colored purple could be commanded by that number of jetß, the boundary line being the river on the west and north sides, on eaßt by Madras street, on the south by midway between Tuam and St. Asaph itrects. The part coloured light brown represents that part of the city which could be commandod by 8.60 ft. jets, the boundaries being on the north by Salisbury street, on the east by Barbadoes street, on the west by Antigua street and Park terrace, and on the south by South town belt. The part coloured green represents the part of the city which can bo commanded at the extremity of the boundary by 5 60ft. jets, the boundary line on the north being the North belt, and on the east by the East belt. In addition to the above it will be observed I have provided means of sufficient capacity to be ultimately extended to all the populous districts, including Papanui, St. Albans, Bingsland, on to New Brighton, Linwood, Ferry road, on to Sumner, Opawa, Sydenham, and Addington, along which and at the extremities of which mains it will be seen eight 80ft. jets can be obtained. I have also provided for eight 80ft. jets all along the South belt by the railway, where large warehouses are being erected. Hydrants are placed three chains or 198 ft. apart in every direction, as represented by pink circles on tho plan, where by the aid of a stand pipe having four way outlets, that number of lengths of fire brigade hose, each 200 ft. in length, can be attached to any of tho hydrants, so that if ten jets are necessary to be brought into play, three stand points and ten lengths of hose will be required, four lengths being attached to one hydrant, four lengths to the adjoining hydrant on the one side of this, and two lengths on the adjoining hydrant upon the other side of it; thus the the ten lengths of hose could be brought to play upon any house or building in the very interior of any of the blocks. The description of hydrant I should recommend to be used is that known as Patterson's 4-inch hydrant, at a cost of about £4 each in London. They are the cheapest and most efficacious. They are opened by means of a horizontal slide ; the process of opening is quick, and the waterway is clear. PBBSST/BE BEDtTOBB. " I should also recommend a Deacon's Automatic Boducing Valvo to be fixed upon the main in Cathedral square, so as to command the whole city, and reduce the high pressure at such times as it is not absolutely needed, a great saving, both in consumption of water and in wear and tear of fittings would be effocted. WASTE PBBVBNTBBS. " I recommend the city to be divided into 20 districts, each one to comprise an equal area as possible, so as to contain when fully populated, 2500 persons to each district, each of which to bo supplied through Differentiating Waste Water Meter, by which means waste is readily detected, diagrams of the quantity wasted being automatically drawn. The saving from the cauße, over and above that produced by ordinary inspection without the meters, is seldom lees than 25, and is often 100 per cent. In Liverpool the whole of the books are kept, and the necessary calculations made in connection with the waste water meter system, for a population of 672,000 persons, by one clerk, whose time ia about half ocdupied in the work. The distribution of the water, if carried out in accordance with my recommendations, would be as perfect as it is possible to design it, and Christchurch would be in possession of a fire prevention service superior to any city I know of, the remotest part of which would be commanded by 5-60 ft jets, e»3h playing 150 gallons per minute, or a total of

750 gallons per minute, whilst the more important and closely built parts with high buildingsjwould be commanded by|lo-80ft jets of 150 gallons each, or a total of 1500 gallons, or if two fires occurred at the same time, 750 gallons per minute could be thrown upon each._ With Buch a system of fire prevention as this, insurances should be granted at very low rates, which would make a very considerable reduction to the ratepayers' annual expense, and would make the water rate scarcely worth mentioning; moreover, with, such protection, merchants and othors would not deem it necessary to insure to the extent they do at present. HOTTBB SERVICES. " I have not included the cost of laying any house services, as it is difficult to say what number would be required for domestic purposes for some time to come. COST. "I have gone very carefully into this matter, and lam of opinion that the complete scheme, including engineering expense? and capitalising working expenses, would cobt £135,000. This is by no means an extravagant amount for a gravitation supply, when estimated at per head of population provided for, viz , 50,000, being only £2 14s per head for a supply of 20 gallons per head. " Several gravitation supplies in Knglnnd with which I am acquainted, of similar proportions to this, viz., ono million gallons per day for domestic consumption, for in ■ ance: IMaxim'm: Cost Popula-i Constant i Total per 20 tion. Daily Cost. gala per | Supply. head. Ashton-nnder I gallons. Lyne ... 70,073 1,000,003 £IIO,OOO £2 10 0 Blackburn ... G 3.000 1.100,000 170.713 2 9 0 Swansea ... CO.OOO 1 1,300,000 100,000 211 0 The average cost of gravitation schemes being from £2 to £2 10s per head of population, so that the proposed scheme cannot be considered an expensive one by any means, more especially as the quantity provided to be delivered, including the reserve for fire, amounts to 4,459,000 gallons per day. I have only to say that it would occupy at least fifteen months to complete the works from the time of ordering the pipes. " I have, &c, " W. P. Htjbbabd, " Of Hubbard and Brown, " Civil Engineers, &c, " Christchurch."