WAINUI WATER SUPPLY.

New Zealand Mail, 22 April 1887, Page 19

WAINUI WATER SUPPLY.

REPORTS ON THE WORKS. MR. HIGGINSON’S REPORT. At the request of the Waterworks Inquiry Committee of the City Council, Mr H. R. Higginson, M.1.C.E., has reported on the Wellington water-supply. Following is a precis of his report:— DESIGN. Mr Higginson considers that the general principle of the scheme appears to have been well considered and suitable. The summer flow of the river was probably ascertained to be in excess of anticipated consumption for many years to come, consequently no storage was provided. Many details of the scheme require alteration, though the general design is suitable and well considered. THE STREAM AS A SOURCE OF SUPPLY. It is pointed out that the present summer has been an exceptionally dry one, and that, though snch a drought might not occur again, we should be prepared for it. As no storage is provided the supply is governed entirely by the discharge of the stream, which must vary with the rainfall. When Mr Higginson visited the reservoir on the 21st ult. he found the river very low indeed. The flow there was 3,095,000 gallons, equal to a supply of 119 gallons per head for the present population. He considers that for domestic purposes and street and garden watering 40 gallons per head per diem is an ample supply, not including that supplied to the trade by meter. This would be the average per diem. The maximum demand would be double this, or SO gallons, which, being taken during the day, would govern both the consumption and pressure. Strict regulations must, however, be enforced to maintain it at that rate. In accordance with the increase for the last five years the population of Wellington will probably double in the next ten year 3. This should be anticipated. POWER AND TRADE SUPPLY BY METER. Mr Higginson calculates that at present we should use 121 horse-power for domestic purposes, etc., and still have 176 horse-power for sale, making up the total of 297 horsepower, which represents the maximum that can be obtained under any condition of pressure maintained or water consumed. This is the theoretical horse-power. “ In another column (he says) I have shown what is termed the efficient horse-power, or actual power given out by the machine used by the consumer for developingit. The best machines (turbines, where the pressureis high), seldom develop 8-10tha of the theoretical power, and I consider it very improbable that even 6-10ths is obtained from the machines usually

employed. I have adopted 7-10fchs as a mean. From a return of water sold by meter for power and trade purposes during February, I find that it amounted to 9,692,000 gallons, which, divided by the working days in the month, gives 440,515 gallons per diem. This represents a large proportion of the water now flowiug in the stream. If the quantity used per diemby meter be consumed during the eight working houra of the day, it will amount to 55,068 gallons per hour. The discharge of the stream on the 21at amounted to nearly 129,900 gallons per hour, so that the meter supply represents nearly half the whole under present conditions, especially when it is considered that probably noli more than 5-6ths of the water iu the stream reached the mains, the other 1-Stk being lost by leakage. It is evident that the amount of water available for sale by meter depends upon the domestic consumption and prevention of waste, and unless the two latter are reduced to within reasonable limits, there will soon be little to spare far the purpose.” OPINION OF CONSTRUCTION AND CLASS OF WORK. Under this heading Mr Higginson says : Several of those portions of the race which had leaked so badly were opened up for my inspection. I found that the loss of water had been much reduced by caulking the exterior with sacking, and cementing the interior, which was the best thing tiiat could be done within so short a time. Upon examination of the whole line of the race, I found that leakage exists more or less throughout. In many cases what seemed to be a large leak was an accumulation of smaller one 3. In two plafees where the race had been carried across an embankment, the settlement of the ground had been followed by the invert of the race, leaving the sidewalls and arch in their original position. This action, of course, left a wide crack upon both sides, which must have allowed a large quantity of water to escape ; aDd the only wonder is that no more serious damage ensued. There is no use in ray enumerating all the cracks and leaks that I was shown ; they were, however, very numerous, and the means of allowing a large quantity of water to escape, in most cases through the loose stony ground, and only appearing iu places upon the surface. I think that most of the leaking occurs between the invert and the side walls. The invert was first constructed, after which the side walls were raised upon it. It seems that before building the walls the old work was not cleaned or properly cleared from clay and other dirt, which would naturally collect upon it. The result has been that the clay and dirt has been washed out, leaving crevices at A A on sketch. The concrete is described to me as being of a varying description in the interior, in some places being apparently good, and keeping a good surface; in others more or less worn rough and into holes. I could not examine the interior, but what I saw of the exterior seemed generally of good quality. In a work of this description it is impossible to supervise every shovelful of concrete that is mixed ; should any scamping have taken place, it would probably occur in patches, and no cursory examination can enable me to decide such, a question. From what I learn, and what I saw, I am of opinion that the damage to the race has been the result oE careless treatment, and work badly put together, and not so much from bad material. The leaks, to a great extent, are the result of a bad junction between invert and side walls, and also in consequence of the workmen neglecting to remove the upper portion of the invert beneath the side-walls that had probably been disturbed by the men walking upon it. All looee portions of concrete so disturbed are no better than loose gravel, and would not afterward set so as to be even approximately watertight. The damage to the hottom of the race has, I am confident, been principally caused in the same manner, viz., by the men making a highway of it with hob-nailed boots before it was properly setThe whole of the loose portions and pebbles would be soon washed ont and rolled along by the water, which has a velocity when running full to the springing of 3-£ft per second. Cracks probably occur in places owing to settlement of the ground, and, considering the amount of leakage, the only wonder is that no serious slip has taken place. There are not sufficient man-holes left. Before commencing repairs, these should be made at most 3. chains apart. , , . . I find that the main pipes, 30in and 24in in diameter, wore ordered to withstand a working pressure of 300 ft, and proof pressure of 500 ft, with exception of 440 pipes 24in diameter, of greater weight and thickness, which were laid on the slope from the long tunnel toward the Racecourse. The actual working head on the 24in mains from the foot of the hill to Wellington is 394 ft, or nearly 33 per cent more than was provided for. These pipes are fth inch in thickness, whereas by all the rules given as the result of practice, they should have been from lin to l-l-16th-in; so that as constructed they are decidedly weak. I have been furnished with a list of failures in the pipes between the 21st February, 1881, and Bth January, 18S7. The result shows that the percentage of bursts in the main pipes is small, being for the 30in mains 0'24 per cent, and for the 24in mains 0*33 per cent. The failures in the joints of these is also reasonably small, being for 30in mains 0 42 per cent, and for 24in mains 0’69 per cent. The joints of these pipes were caulked by Corporation emploj’ds. The 21in mains in town were laid by contract, and caulked by contractors’ men, the percentage of leaky joints being 6‘30 per cent. The lesson to be learned from this Is that all joints should be in future made by day labor, and not by contract. I might here point out that the space for lead in the sockets of these pipes is not designed to withstand the very high pressure to which they are subject. As constructed, the expansion and contraction of the pipes is likely to draw out the lead at intervals and leave it so. The contraction may withdraw it even only 1-32 of an inch in places, but the expansion will fail to replace it. This action, often repeated, will cause the joint to fail. The better plan is to widen out the lead space slightly inside, which effectually prevents its being extracted in the manner described. Mr Higginson considers that at the point where the 30in main crosses the Wainui river bed they are laid too near the surface; and that there should have been two more sluice-valves in addition to the one now in

use, at each crossing of the A’V amui. The sluice-valves between the tunnel and Weilington are two small. He thinks the Gin air.shaft at the Wellington end of the tunnel is a very good arrangement. ALTERATIONS AND ADDITIONS RECOMMENDED. Mr Higginson advises telephonic communication between Wellington and the Wainui and Karori reservoirs. That, as soon as the 12in main is laid to Karori and proDerly tested, the Wainui service end be cut' off for repairs. The repairs to the race are the most important, and will require the longest time to cute. He does not advise that the whole interior be rendered with cement, as he does not think it could be made to adbere to the present surface, unless all picked oyer and the skin removed. The better plan would be to properly repair all cracks and crevices, and fill up irregularities and holes — this would arrest all major leaks. The minor leaks which exist throughout the . whole length more or less could, in his opinion, be best arrested by excavating the present rocky filling upon each side of the walls (where not solid rock) for a width of about 15 or loin, and re-filling the trench with well-puddled stiff clay of the right sort. This would be better calculated to arrest leakage than any cement work inside, which, unless very carefully done, would flake off again. It is a well-known fact that no ordinary concrete of reasonable thickness is water-tight, and that any concrete wall used for retaining water is always backed by clay puddle. The puddlework suggested could be commenced at any time, ancf done by degrees, and the cementing and repairs to the interior when the water was turned off. A properly constructed scouring valve should be procured, and fixed when the _ race repairs are effected. The mams at the river crossing need protection, and shou-d be done at once. An Siu valve should be faxed at the first Wainui crossing, and a 10m valve at the second crossing. He suggests the immediate removal of the Petone valve, and that mean 3 should be taken to test the mains for leakage at Petone and Kaiwarra. He does not consider that it would oe advisable to construct an extension of the 30m mam from the well to reservoir, as the cost is too great for the advantage to be gamed. The Wainui reservoir can hold a very smal. amount of water after the top oft has been drawn off bv the race. The storage capacity is bein" reduced yearly by the accumulation of shingle, and it can in no light be considered a storage reservoir of any value ; it, however, answers well a 3 a settling pond, for which it was designed. recent consumption. Mr Higginson states that one of the gauges in the City Surveyor’s office requires to be cleaned and put in order as it could not be relied on to read within 71b. The results obtained proved that no reliance could be placed on the gauges, and they had been abandoned in consequence. Slightly more than the 3,095,000 gallons per diem flowing into the reservoir was flowing out. He could not measure the water escaping from -he sluice and race, as no reliable results could be obtained. He estimated, however, that at least 2,600,000 gallons must have been passing into the pipes, or 100 gallons per head. He recommended that a meter should be obtained for testing consumption and waste. He could not help thinking the loss of pressure may be to some extent explained bv the omission of scouring s^jice3 a . tne want of proper air valves. There being no means of clearing the pipes at the above points, what has become of the shingle and other material washed out of the race . The velocity of the water m the 30m main, at the maximum rate of consumption allowed for, is less than 2ft per second. The velocity would move small stones along a level pipe, but not convey them uphill. Thpre is hardly any movement of water in the p& a “rig the hoars a! night,, so that daring goods, when the water is dirty, a deposit Will take place, which, mixed with shingle and other debris from the race, will gradually form an obstruction whicu will reduce the discharging powers of the pipes, and probably account for the loss of pressure m the day-time. The presence of air m the nines unable to escape forms another serious obstruction. The only other way m which to account for the pressure falling to say, 901 b per inch, while the full head is maintained, is a truly extravagant consumption, amounting to 6h million gallons per diem or 250 gallons per head. That a certain amount of waste occurs from leakage of pipes and fittings is a certainty, the diffi culty being to determine what that amount is This waste is present in every BU Pply. and, in the case of Wellington is probably excessive, owing to the extraordinarily hq£ pressure, which is much in excess of what is generally allowed. measures for checking waste. Careless and extravagant waste can be checked by strict supervision. The waste by defective pipes and fittings is not so easily dealt with. Deacon’s waste meter has lately been much nsed for this purpose the coati of applying which in Glasgow is £39 15s 4d, and \ere would probably cost £SO or £IOO. A simple method of ascertaining the waste is to convey an ordinary meter of the necessary size, with two lengths of hose and hydrants, in a waggon or hand-cart to the place required. By attaching tlie 5 0 ses to hydrants on either side of a stop valve, with the meter between, and then. closing the valve in main pipe, the water is all passed through the meter. A very short observation will tell whether the flow is more or less than it should be. Of course, the district under observation must be disconnec-ea from all supply except through the mam to which the meter is attached. This is the method he would at present recommend for ascertaining the consumption between 1 ando a.m., and from the result discover the probable loss from leakage. Rules and regulations should at once be drawn up and printed for the guidance of plumbers and consumers. They should describe the manner m which all water-closets, cisterns, and other fittings are allowed to be put it, and also the manner in which all overflow pipes from cisterns should be constructed. All overflow pipes should discharge outside the house, so as to be at all times visible to the • Inspector. Printed forms should also be used by the Inspector, to be left with consumers at whose houses defective fittings are found to exist. Certain classes of fittings should be choßenas suitable for use, and samples kept at the Corporation office for reference.

future extension. Mr Higginson has been informed that some years since a survey of the country between the Wainui and Orongorongo drainage basins was made, with the object of ascertaining the feasibility of leading the water of the latter river into the Wainui, in order to augment the supply to the present works, and that the result proved it possible at a very reasonable cost. Ho would advise that this matter be definitely ascertained, so that the drainage area may be at once reserved from sale. It is in this direction that an additional supply must be looked for. Storage reservoirs upon both streams can then be left for future generations to carry out. KARORI SUPPLY. Mr Higginson says the City Engineer informs him that the amount of water stored is 9S million gallons. The total head to full water-level is 450 ft, and the average level he had taken at 432 ft—the equivalent pressure beiDg ISTIbs. The amount capable of being discharged by the 12-inch maius, when completed, will be about 2,900,000 gallons per diem at a pressure of 1201 b in Wellington. Taking the average domestic supply at 40 gallons, and meter supply at 17 gallons, making a total of 57 gallons per head per diem, which should be ample if waste were prevented, the above supply should last 66 days. This is not allowing for any supply running in during that time. He would advise that the new 12in mains be laid and tested, before depending upon it for sup. plying the town while repairs are made to the Wainui works. The pressure will reach 1951 b per square inch, and as none of the pipe 3 were designed to stand so much, it is only reasonable to expect numerous bursts. He considers that this supply, in conjunction with the Wainui, should be sufficient for the city for many years, if properly managed. lor the greater part of the year an abundance of water runs to waste over the Wainui bywash, and it is only during the summer months that auv failure in the supply is likely to occur, even during such a season as the last, when nearly 120 gallons per head per diem was yielded by the stream at its lowest. PLANS. In conclusion, Mr Higginson remarks that none of the plans of the water-supply are in a properly finished state, and recommends that all plans and drawings be finished. The City Surveyor, he says, has given him all that was in his power to give, but it had to be obtained in many cases second-hand—-from, meu who had been employed during the construction of the works, and which information he had been obliged to accept as correct. He had also been unable to obtain a copy of Mr Clarke’s report.

THE CITY ENGINEER’S REPORT. The City Engineer and Surveyor (Mr B. Loughrey) having carefully perused the report of Mr H. P. Higginson, states that “Although I agree with it in the main, as seen by mv various reports from time to time to the'City Council, yet there are some points on which I beg to differ, more especially as to his suggestions for necessary alterations and additions and methods of carrying out the same, which I respectfully submit is within the province of the City Surveyor.” Alluding to the supply and design of the work, Mr Loughrey says : —“I also, like Mr Higginson, had been led to understand that thishad been approved by Mr W. Clarke, an eminent authority, and have, therefore, no remark to offer further than I consider that as the Jreservoir fis only intended to act as a settling pond, and not for storage purposes, it would have been much better, in the first instance, had the cast-iron mains been laid direct to the reservoir, thus dispensing with the race and well, the latter more particularly, as the advantage to be gained by it appears to me very questionable in comparison with its obvious disadvantages, among vhich latter I may points out the difficulty of at all times regulating the supply so that a full head of pressure is maintained in the well, and at the same time the waste at the bywash prevented. Had the pipes been laid to the reservoir at a level of 10ft below the level of the present race, I submit there would have been no necessity to shut off the water from Wainui, as the flow of the river, aided by the extra quantity stored in the reservoir, would have been sufficient to meet all requirements, and the head of pressure would not have been always varying, as is mentioned by Mr Higginson as happening at the well.” Referring to the stream as a source of supply, he says there is no doubt that at the time of gauging for the scheme the quantity flowing in the river was ample fortherequirements of the city for many years, and he had no hesitation in saying that the average annual stream is also ample now, but storage is required during the wet season, and this can be obtained at various places along the stream at comparatively small cost, as he had previously reported to the Council; and he must here beg to differ from Mr Higginson, and recommend the utilisation by storage of the present source of supply, which is as clear as crystal, and leave the_ Orongorongo to future generations, especially as the maximum supply possible by the present mains is 5,091,840 gallons per diem, and the Wainui stream at its largest would supply more than double this quantity. This, as was well known, had been an exceptionally dry season, but the quantity of water coming in had been more than ample for the population, only the people had been educated to waste the water at will; and it was needless to say that he concurred with Mr Higginson in the amount for sale by meter depending ufaon domestic consumption and waste, as was quite obvious. With regard to the construction and class of work, the Committee were doubtless aware that the only portion ot the construction with which he was concerned, either directly or indirectly, was (in conjunction with Mr Blackett, as Consulting Engineer) in effecting the repairs to the face-wall of the dam, which had been washed away previous to his arrival in the Colony, and laying the three 24in sluice-pipes and the cushion-wall. With these exceptions, the work was handed over to him as completed, and, had the accident to the dam not occurred, the water would have been turned on to the town. His predecessor obtained leave to attend to his private concerns directly after his (Mr Loughrey’s) arrival), and nothing was mentioned to him as to there being any likelihood of the race subsiding m

any part; and the probability of such a contingency not having been thoroughly provided against in a work of this importance would not, he imagined, occur to any engineer. With respect to the inspection ot the interior of the race, that also did not seem to have been considered needful, as its construction, 2ft 9in high in the highest part, would not allow room to make repairs, were such required, and the great scarcity of manholes still further increased the difficulties of proper inspection; but such interior examination, he maintained, should have been entirely unnecessary, with the very slight fall (9ft 6iu iu a length of 2110 yards, or 1 in 660) had the work been performed with thoroughly good material in a reliable manner ; the rendering of the interior, if properly done, should have made it watertight for a century with so slight a flow, and the race never running more than half full. The causes for its failure to do this may be as stated by Mr Higginson, but it does not alter the fact that the workmanship at least must have been faulty. . He quite agreed with Mr Higginson that the rules and regulations for checking waste should be more stringent.