CHRISTCHURCH WATER SUPPLY.

Globe, Volume XXIV, Issue 2527, 16 May 1882, Page 4

CHRISTCHURCH WATER SUPPLY.

At last night’s meeting of the City Council the water supply committee reported that for a water supply for the city of Christchurch, the cheapest and most efficient method was Holly’s pumping system. The committee, therefore, requested Messrs E. Dobson and Son to favor tho committee with a report on that system. The report, copies of which are to be sen 1 to each councillor for consideration, was tabled. It reads as follows : We have the honor to acknowledge the recsipt of your letter of the Ist inst., and in reply beg to hand you the following report upon a water supply for the city of Christchuroh. We have already advocated the Holly system ag most suited to the requirements of the city, and we consider this view i§ fully proved, when tho conditions of tho case and the advantages of the system are fairly taken into account. Christchurch is differently situated as regards water supply to roo«t towns in New Zealand. A large domestic supply of pure water already exists, and although in some parts of the city tho artesian water from the upper stratum will not rise to the surface, it can be easily raised by a pump. Therefore, at present, no considerable revenue could be expected to be cleared from the sale of water for domestic purposes, and the scheme must bo considered primarily for fire extinction, and street and sewer cleansing, water closets, &o. , , With this in view, it ie obvious the scheme should bo devised on such a scale that, whilst meeting tho above requirements in the first instance, and being capable of supplying double the present population with pure water for domestic consumption (when required) Jthe cost should be such as would rot materially increase the present rates. The artesian supply to bo obtained by patting down cylinders in Christchurch to tho lower stratum is practically inexhaustible, being derived from an immense natural reservoir of saturated shingle, which is tilled by filtration from tho Waimakariri, and is for this reason unusually pure in quality, whilst the float is sufficient tu throw the water several feet above tho surface of the ground in the highest part of the city. By sinking wells of sufficient size and reticulating tho city abundance of water would be provided for all sewer flushing, street cleansing, and domestic supply without pressure. By putting on a Holly pumping engine, capable of raising 2,000,000 gallons of water per day under a pressure sufficient to throw six lin jets 130 ft high, the city would bs secured from any serious loss by fire. The cost of such an engine, erected complete, would not exceed at the most £IO,OOO. including the buildings, &c , and the annual expense of running to supply all the present requirements would not bo more than £ISOO per annum. Thus the annual cost of putting pressure into the mains to suit all present requirements under the Holly system would be—£lo,ooo at 5 per cent. ... £SOO Sunning expenses ... ... £I6OO Total £2OOO Whenever a demand arose for water, for domestic use, ns would be sure to be the case in all the larger bouses as soon as its advantages were known, the cost of the extra work done by the engine would be far more thau covered by the charge made for the water. Bat on the other hand to obtain pressure by gravitation tho main must bo laid down at once, to give the greatest quantity that may be required in time of fire—thus to be equal to tho engine before described, it must be of sufficient size to deliver 2,000,000 gallons per day under pressure. As an 18-in main has been fully diooussed in previous reports supplied to your committee, it may bo well to take it as a standard of -comparison, although it would be slightly in excess of the ability of the engine, being able to throw seven j?ts 130 ft. high. Prom the site proposed for efftake works at the Waiznakariri by Mr Blackwell, the distance to Obristohuroh is about 17.) miles, and the main would cost at least £78.750, which at 5 per cent, would be an annual charge of £3937 10s. This gives a present saving in favour of the Holly engine of £1937 10s per annum, and a debt of £78,750 to be paid some day in the former case, as against £IO,OOO in the latter. Another point in favor of the Holly system in comparison with a pressure main which deserves attention is that the draft for domestic supply varies greatly during the day, the greater portion being taken between 6 a.m. and 11 a.m. Assuming a population of 33,000, consuming 30 gallons per head per diem, they would in all be using at the rate of 100,000 gallons per hour during this time, in which case, with the 18in main, the piessure would be so reduced thatit would onlv be sufficient to throw a single lin jet JLOOft high, and in the case of fire occurring there would not be sufficient water under pressure available unless the reticulation were arranged as would enable the domestic supply to be out off, which would not be advisable. It would therefore be necessary, by the time the population reached 33,000, to have a larger pipe, or doubtless it would bo better to lay down a larger pipe in the first instance, as recommended by Mr Blackwell. That gentleman proposed a 22in main, at a cost for the main alone of £85,466. This size would bo amply sufficient to provide for all contingencies, but it would at 5 per cent, give an annual cost of £4273. On the Holly system, so soon as it was found that the domestic consumption was increasing at such a rate as to endanger tho pressure available for fire extinction, another engine of similar size could be erected for £7OOO, and the two together would give ample security, it being only necessary to run the second engine at the times of greatest demand. In comparing the system of pumping direct into the mains with gravitation, it most be kept in view that the cost is always in proportion to the work done, and as Ohristchuroh is on a nearly dead level, a very low pressure at the pumps would be amply sufficient for all purposes except fire extinction, and the pressure could be raised immediately when required, in consequence the daily cost would be low. Our estimate of costs for complete works for the city on tho Holly system is as follows : Pumps £IO,OOO Wells 3,000 Betioulation of city ... 40,000 Contingencies at 10 per cent 5,300 £58,300 Interest at 5 per cent on £58,300 2,915 Coat of running engine for present requirements ... 1,500 £4,415 And for a gravitation echemo with an 18in main— Cast iron main 17) miles long 78,750 Betioulation of city 40,000 Cylinder at Waimakariri ... 2,000 Contingencies at 10per cent 12,075 £132 825 Interest at 5 per cent ... £6,641 5 0 This shows a saving in tho Holly system of £2,226 5s per annum. The annual cost as under the Holly system for all present requirements would be £4415, which on a rale roll of £240,000 amounts to nearly 4id in the pound. But a direct saving would be made in some present items of expenditure, and there would be a small sale of water for trade purposes, Ao. Our estimates of savings and revenue which could be safely counted on would bo as fellows : Or. By saving cost of fire engine ... £IOOO „ Saving cost of watering streets ... 500 „ Sale of water for baths, hotels, &o. 500 „ Sale of water for trade purposes 1000 Total £3OOO The difference between this sum and £4415, the annual cost, is £1415, which is all that would have to be charged against the rates, or rather less than l)d in the pound. Or, in other words, by the addition of a lid rate to the present rate, the city could be guaranteed inn unity from all serious loss by fire, and an ample supply obtained for street watering and sewer flushing, besides giving an ample supply for all present requirements for trade purposes, domestic supply, &3. ; and os the demand for domestic supply increased, the city would in all probability realise a considerable profit. For instance, 1,000,000 .gallons per day at fid per 1000 (which is lower

of pumping it at a pressure si ffident for all domestic purposes could not possibly exceed £IOOO, in addition to the sum of £ISOO already set down. When this state of affairs is reached the account would stand thus : Db. Yearly interest at 5 per cent, on £58,300 ... £'?9ts (lost of runnirg engines ... ’ ... 2500 Balance to credit 5-1-0 £10,625 Cb. By saving in cost cf fire engine ... £IOOO Saving in watering streets ... ... 500 Sale of water... ... ... ••• 9125 £10,625 In the first estimate given of revenue and saving credit has only been taken for what can bo relied on safely at present, but an the present system of soavengering is to bo done away with when water can be supplied to the closets, there will be a saving in that item. And also there will be a very considerable reduction in insurance. The statement might very fairly be.put iu tho following form Saving in annual cost of fire engine ... 1000 Saving in watering streets 500 Sale of water to hotels, baths, &3. ... 500 Sale of water for trade purposes ... 1000 Present cost of soavengeriug saved when closets are connected with sewers ... ... ... ••• ••• 2000 Reduction of insurance, 12) percent.. 3125 £8125 As against estimate of present annual coat ... ... ... ••• 4415 Annual saving to the inhabitants of the city «3710 That is to say, there would bo a direct profit to the Borough of £585 per annum, and a saving to insurers within the city of £3125 per annum. Having now treated with tho general financial question, we will proceed to the description of the Holly system, which, we believe, is new to the Australian Colonies. The Holly system, ao being carried out by the Holly Manufacturing Company, is intended to suit oases similar to Christchurch, where there is abundonoe of water near at hand, but where a great outlay would be required to give pressure by gravitation. The pumps are designed to drive the water direct into the mains, thus saving all cost of a reservoir, with its necessary connections. The engine is quadruple, having four cylinders working four pumps, which may be worked by high or low pressure. Bach pump can be worked separately, or two, three, or four bo worked together as required. Therefore, for all purpoies of safety, it is equal to four engines. A 2,000,000 gallon set of pumps would comprise in addition a duplex pump as a reserve for use in cases of emergency ; also built to work separately or together. Air vessels prevent all shocks to the pipes and machinery, and an automatic regulator maintains the pressure to whatever it is set to by the engineer in charge. The following extracts from various official reports will show the power of this class or machine. At Rochester (N.Y) two sets of pumps were erected—a four-million sot driven by water-power, and a three-million set worked by steam. “ With both sets at work, the following results of trials were recorded: thirty-one i -inch jets were thrown simultaneously 135 ft. high { one 3-inch jet, 285 ft ; one 4 inch jet, 297£t; and one 5-inch jet 250 ft high.” As showing tho power tno pumps have of maintaining a pressure through a length’of reticulation, tho following is interesting:— At the same time as the trials mentioned before were made. “ At 2) miles from tho pumps, and 28ft above tUom, a pressure guage was put upon one hydrant nozzle, and a length of 50ft of hose with 1-inch nozzle on the other ; a signal was given from the fire box to the engineman to put on lOOlbs per square inch pressure at tho pump-house. The hydrant was opened at 2.30 p.m., and at 2.31 tho gauge inchoated about 701 b. and remained nearly stationary until 2 37 p.m. The altitude measured instrumentally was 125 ft, and the length horizontally 140)ft. At 2.38, two additional 1-in streams, each through a length (50ft) of hose, were thrown from an adjacent hydrant; at 2 38), the gauge indicated 701 b with three fine lin streams playing; at 2.39, it rose to 741 b, which was maintained until 2 42 p.m., when the hydrant was closed.” These streame wore all 125 ft high. At Atlanta, Georgia, a two-million set of pumps was erected ; the pumps were 4£ miles from the city, and 360 ft below its greatest elevation. At the official trial of the works, six lin jets were thrown 160 ft high ; the water pressure at the pumps being 2251 b to the square inch, and at the hydrant 1501 b. At Hyde Park, 111 , six one-inoh streams were thrown from hydrants, eight miles from the pumps, with a water pressure of 1091bs at the hydrants, and 1291bs at the works. We could quote numbers of similar examples, but consider the above will be sufficient to show the capacity of the pumps and their suitability for the work required in this city. It has been generally considered to ensure a duo supply, and to guard against the chance of being without water by a break down of the engines, that in all pumping schemes a reservoir should be constructed, if possible, at a sufficient elevation above the town to give the required pressure, and tho water is pumped into the reservoir, from whence it flaws by gravitation into the town pipes ; and tho reservoir is frequently constructed to hold several days’ supply. It is held that a smaller engine may be used, as it can be always run steadily up to i s full power, and that there is a saving in the cost of pumping and attending. Under these conditions, it is evident that the reservoirs should be of sufficient size to hold such a quantity of water as would suffice for all requirements during the longest time an accident would probably stop tho pumps. Reservoirs are frequently constructed to hold from five to ten days’ supply, and in many oases a far larger quantity. Assuming, in the case of Ohristchuroh, that a seven days’ supply of 1,000,000 gallons per day would bo sufficient, the cost of a reservoir system, added to the works already estimated, would be approximately as follows £ Rising main, and force main from the Port Hills—total distance say 4’4 miles ... ... ... 17,000 Reservoirs to hold 7,000,000ga1s ... 15,000 Total £32,000 The city would then be sure c£ a seven days’ supply, whatever happens the engine ; but on the other hand an accident might happen either to the rising or forcing main, or the reservoir might leak and be a source of continual trouble and expense. In this instance tho additional cost as compared to the Holly system would be the annual interest on £32.000 at 5 per cant,, say £1600; against which is to be placed the less first cost of the pumping machinery, and the saving in pumping and attention. I In the first of the two items there might be a small saving, but it would not bo of sufficient amount to make any perceptible difference in the annual interest, and the latter is more fancied than real ; because all tho water used would be at high pressure, and the engine would have to work at all times against the column of water in the rising main. Whereas with the Holly system tho pressure would be adjusted to meet the requirements of the hour, and tho same amount of safety could be attained at a much loss cost by having a duplicate set of pumping machinery. Mr Crafts, 0.8., gives the following comparison : Tho City of Boston Ims recently canotruotod a reservoir on Parker Hill for the benefit of a portion of the high service previously supplied through a stand pipe. The quantity of water delivered daily is about 1,600,000 gallons, and tho cost of the land, reservoir, and connecting mains is not far from ... §250,000 The Chief Engineer now proposes to supplement and extend the high service system, and proposes two more reservoirs at a cost 0f... §350,000 To this add probable cost of long lines of connecting mains, say ... $200,000 And we have a total expense of about ... ••• -•- ••• 5800,000 For reservoirs and force and connecting mains to supply a present demand of less than 2,000,000 gallons of water per day. If a comparison is wanted, take Bangor works, under the “ Holly system,” with an engine of three million gallons per day at ordinary speed, a reserve rotary of four millions for occasional nao, engine and boiler house, filtering cribs, seventeen miles of distribution pipes, and one hundred and twenty* seven hydrants, the entire cost of which was

Parker Hill reservoir and connecting main above have cost. We have oolleated a great deal of information respecting the Holly system, which we should be glad to lay before you should yon require it. The result o£ our enquiry is that the Bystem is gaining ground rapidly in America, and although a late invention, it was in 1876 in successful operation in eighty-five cities and villages, having populations varying from 2500 to 130 000. We have no henta tioa in recommending it to the favorable consideration of ycur committee.

Wo have, &b„ Ebwakd Dob-on and Sox, M. M. Inst. C.E