TOWN WATER

Southland Times, Issue 20666, 23 April 1929, Page 9

TOWN WATER

MR CORKILL’S REPORT REPLY BY FORMER ENGINEER THE DUNSDALE SCHEME The following letter addressed to the editor of the Southland Times, has been received, from Mr G. F. Glapcott, of Napier, who was for some years town engineer at Invercargill:— Having read the borough engineer’s report on the above in which he comments in no very favourable terms regarding the reports, submitted and works carried out by the three late engineers, I trust you will grant me space in your columns to reply to .same insofar as my activities in connection therewith are concerned.

Any person reading the report would certainly be lead to believe that Mr Corkill’s predecessors had reported favourably on matters without first making themselves conversant with the conditions relating thereto and thereby misleading the ratepayers. Further that plant had been installed at the pumping station unsuitable for the purpose. Possibly Mr Corkill did not intend it to read in this light. But the report is certainly open to such construction. Apart from the tone adopted in referring to what had been done in the past by his predecessors, I wish to compliment Mr Corkill on the very clear manner in which he has presented his report. The whole (subject has evidently received careful consideration, and although I do not agree with all the conclusions that he has come to, this fact has, at this stage, little bearing, further than that I wish to traverse past operations, and express my views on matters as they stand to-day.

Dealing firstly with the proposed Dunsdale gravitation water supply:— I was at the time instructed to report on a scheme for supplying from either underground or by gravitation a supply of water equal to one million gallons per day.

Before recommending any scheme I inspected the Oreti River at Dipton and also at Josephine. The Mataura River, at Mataura, also the Dunsdale stream beyond Hedgehope. Objections to Dipton Proposal.

My objections to the Dipton proposal were depth of intake at the site—uncertainty as to the river always maintaining its present channel—trouble with the water during periods of heavy flood, and length of pipe-line. The question of dealing with the drainage from- the Dipton township, which discharges just above the intake, this could be easily diverted to discharge below same.

The Oreti River, at Josephine, and also Mataura River proposals, 1 turned down. Dunsdale scheme I favoured in preference to any of the above and also pumping. In connection with the Dunsdale, the following investigations were made:— 1. The quantity of water in the stream during dry weather, and also control of the catchment area.

2. Site for pipe-line intake. This could be either at the falls, or lower down. Area suitable to form a storage reservoir when such was required.

3. Levels of both sites above the town. The fall’s site, if I remember rightly, is 90 chains approximately beyond the lower site and considerably higher. 4. Location and inspection of pipe-line, and dimensions of pipe to provide the supply of water specified. 5. Estimated population to be supplied during a period of say 25 years, based on statistics for past 15 years. , 6. Cost of steel pipes, cartage and delivery of same along the line, also trenching and laying. All .the above costs were based on first-hand information received from manufacturers and cartage and pipe-laying contractors.

7. Inquiries made re “life of steel pipes” and replies considered from Melbourne and Johannesburg.

8. Stand-by plant in town for emergencies.

9. Samples of water sent to Mr Mclndoe, analyst, and his report on same. Before finalizing on the position most suitable for the pipe-line, the. route was traversed twice on foot from the end of the North Road at the Makarewa River to the proposed intake on the Dunsdale. I might say that after each trip my companions and I were a tired crew. I did not adopt the Titipu Hill and Main Road route on account of the high elevation and extra length of main. Regarding site for the dam and testing same by borings, this latter work in my opinion was not essential at this stage. More particularly so as one is not bound down to building a concrete wall as there is immediately adjacent thousands of yards of spoil to allow of an earth embankment being constructed. The Dunsdale dam will only be a small affair, in fact I only provided for a weir. I quite agree with Mr Corkill that this site should be tested; particularly so before attempting to build a concrete dam.

Regarding the dry weather flow of the stream —the gaugings were taken during different years and at particularly dry periods. Assume that the.se have been overestimated, the storage facilities' will more than provide for any contingency that may arise. Southland is not subject to long periods of dry weather.

How many towns are there that can tap a stream of sufficient capacity that, during dry weather, will meet requirements indefinitely without storage? Personally, I consider there need be no concern regarding the adequacy of the supply. There is no doubt the borough has a very valuable freehold asset here whether it be used now or in years to come.

I consider that every reasonable investigation concerning the scheme was made at this stage to warrant a proposal being submitted.

In reporting to-day, 17 years later, various factors would require reinvestigating. Such as dimensions and class of' pipe and population to be served. Again we have to-day first-hand Dominion experience on the life of steel pipes as there are several existing pipe lines laid 20 to 22 years ago. About the time I reported various classes of pipe were laid in the borough with the object of gaining definite information on the life of same when required at come future date. Wood pipe in Avenal Road, west of North Road—Lapwelded steel gas main in part of Kelvin Road—spiral steel sewer pumping main in Levin street. The latter was adopted on the ground of big saving in cost compared with cast iron, and also on the advice of the late Mr Mestyer, consulting engineer of Wellington. The saving in cost capitalized was sufficient to pay the cost of the sreel pipe within 16 years.- This period has now expired. Underground Supply.

The. .criticisms contained in the .report relating to the pumping plant (surface and underground) would not, I feel sure, have been expressed if Mr Corkill had made inquiries and made himself conversant with the facts and conditions prevailing at the time that the plant was installed. The lack of accessibility to printed records has little or no bearing on this particular subject.

Firstly, I accept responsibility for the installation of the major portion of the plant as it stands to-day, and which has done good service for a number of years past. Coming on the scene to-day, I agree that improvements with sufficient money available- can be carried out. Traversing the periods during which the various power units and bores were installed we have—firstly, the sinking of a 6-inch test bore in the reserve south of Yarrow street. Results not satisfactory. This was followed with another 6-inch bore now known as No. 1 adjacent to the old well. Following this, a deep bore was sunk as a test for an artesian supply. Result nil. As extra water was urgently required an air lift was installed at Na 1. The only method of panqs-

ing that pennite of obtaining a maximum supply from so small a bore, and at the same time coping with sand and grit which for some considerable time after a bore is sunk gives trouble. Following this tenders were invited for sinking a well, and driving adits to supplement the supply to same. In the event of it proving impossible to sink the well to the depth specified, a large cylinder or bore was to be driven down from the bottom of the proposed well to the water-bearing drift. This alternative was not included in the contract. The lowest tender for the well was £9600. This was declined, and rightly so. Following this I recommended the sinking of a 22in diameter bore, same to be put down clear of the radius of draw off from the existing old well. After some consideration, the council approved of the bore being sunk, but fixed the site as now existing, close to the well. Tenders were received for the supply and installation of an Ashley bore hole pump of fairly large capacity. The tender was, if I remember rightly, £3OOO or closely approximate. This tender was also turned down on account of no assurance being given by the makers that trouble would not arise if a certain quantity of sand or grit passed through the pump when pumping. The council also cabled to Guildford (a town in England where one of these pumps was operating) and the reply, I remember well, was: “Pump very satisfactory providing no sand or grit.” I might say that at this period, bore hole pumps of the centrifugal type now in use were then in the experimental stage, and not to be recommended. Just after declining this tender, the war started, and from then on the council, like many other local bodies, was faced with having to take whatever plant was available, and to adopt means temporary or otherwise to meet the position of providing for a steadily increasing demand for water, due to the installation of the sewage system. What complicated matters further was the gradual fall in the water level in the various wells as the pumping hours increased, and little appreciable gain in the quantity of water flowing into the wells in proportion to the amount of lowering that continued to take place. Later a 6in test bore was sunk jn the Park opposite Fraser’s store. Site chosen by the Rev. Masonresult unsatisfactory. Following this a 6in test bore was sunk and also a 22in bore in the reserve adjacent to Elies road. There, the conditions were most promising for obtaining an abundant water supply. Testing the Gin bore after being sunk the flow was 13,300 gallons per hour and the water level which stood at 44 feet from ground level was only lowered 3ft 6in after four hours continuous pumping. The supply from the 22in bore sunk alongside, gave a supply of 23,000 gallons per hour after pumping continuously for six hours with the present pump. Tlie discharge gaugings were frequently taken. The waterworks staff can, I feel sure, remember the water overflowing the fluming conveying the water to the reservoir. Falling Off in Supply. Mr Corkill appears to doubt the pumping station staff’s contention that the bore is not giving now half what it did originally. Apparently the supply now from this bore is little more than one-third what it was. •This extraordinary falling off is no doubt due to one of three causes or a combination of the three. Referring to the pumping installations, Mr Corkill states that the pumping units (compressors and pumps at the station) are not of a standard size or make. Well, I have been through many pumping and power stations and I can’t say that I have seen one in which the size and make of the various power units does not vary both in size and make, in fact it would be most extraordinary if they did not in a growing town. In this case the compressors were bought wherever it was then possible to procure them, and one of the pumps in the station had to be purchased in Australia-at this particular time to assure delivery. If the air lift is so inefficient, or as stated, the whole outfit, why was the air lift system of pumping extended at so late a date as 15 months ago to the new 9in bore?

The reply is obvious. Because no one could suggest anything better to provide a maximum supply, and at the same time cope with sand efficiently. The efficiency of the system is low I quite agree, but conditions arise when power efficiency be comes a secondary consideration. Given a definite assurance that plenty of water is available, and money permits,' then no doubt a more efficient method of raising the water than now in operation can be installed.

Full information relating to the various bores sunk, depth of water bearing strata is, if not to be now found in the engineer’s office, on record in the Town Clerk's department. The council was kept fully informed as the various bores w'ere sunk. Shortly before the late Town Clerk left, I fancy he was asked by the council to tabulate all the reports submitted on water supply. This file, if compiled, should be available. The first bore was sunk in August, 1910, 19 years ago. If these reports are not obtainable, I have copies of the original particulars in a rough diary containing a lot of irrelevant matter of no value to anyone but myself. I will have the information, which covers water levels, supply from bores, draw off from tower during night hours, etc., typed out and forwarded to Mr Corkill.

Three weeks ago I was given by Mr Stevens, an old Invercargill resident, the original notes relating to the first bores sunk in Invercargill in 1873 which are as follows: Crescent (1), Puni Creek Gardens (1) Hall's Paddock (1), Old Show- Grounds (2) The only recorded flow is the Gardens bore which was 50 odd feet deep. The water flowed 4 feet above ground level. The strata at the other bores which vary in depth to 160 feet is similar to what has been met with later and as recorded in the Municipal Public Office. Plans of the 22in bores showing position and number of slots are in the engineer’s office, and also should be attached to Stewart Bros.’ contracts. There is no lack of records and the reports to the council on this subject must form a very bulky pile. I have no information regarding the strata at the 9in bore as this was sunk since my time. But from the report published relating to same I know that it must be fairly well within the radius of draw off of the existing well in this reserve; and that the supply from the latter must now be affected. In regard to filing, of records it must be borne in mind that the conditions to-day and when boring was commenced are entirely different. Then the engineer’s staff comprised the late Mr Strang and myself and there was one typist to do the typing for the Town Clerk’s department and my own. Needless to say almost all correspondence and reports had to be prepared in longhand. The facilities for keeping the present day system of recording and indexing were non-existent. Conclusions and Suggestions. Reviewing the position as it stands today in conjunction with my experience in the past I have no reason for changing the views that I expressed in the report to the council years ago when instructed to advise as to the most reliable source to obtain one million gallons of water per day. Then I stated: that although the results obtained at the 6 inch bore lately sunk in the water works reserve were very promising that until such source of supply had been tested by continuous pumping over a considerable period no assurance could be given that the quantity specified could be obtained economical' • from underground and that of the various schemes investigated I preferred the Dunsdale. I am convinced after reading the figures quoted in Mr Corkill’s report regarding “supply from the various bores” that the underground supply is not going to be increased by any appreciable extent permanently by concentrating the pumping plant and pumping from a much lower level than at present. The results first obtained under these conditions will possibly be most promising but later the conditions that have led up to the present will be repeated—a lowered water level and less water. This in my opinion is due to the fact that the bores penetrate a saturated area varying in den-

sity and not underground streams as has been and is still assumed. The quantity of water that can be drawn off at one point from the underground reservoir is governed by the density of the strata retaining same and not by- supplies from distant sources. As the storage becomes more heavily taxed by continuous and deeper level pumping the time arrives when the storage is depleted and the water level lowered to the maximum and the only water finding its way to the pumps will be what ever quantity reaches the low level strata by slow downward Alteration from the surface streams, and natural rainfall. To my mind the evidence now appears to be conclusive in this respect. The storage can be relied upon to give a fixed quantity, but only by avoiding lowering the water level below certain limits. Exceed this limit and the result is a diminished supply and a considerable drop in the water level. Continue this and we face the problem of little water and large pumps necessitating throttling them down which results in loss of efficiency. That there is an abundant supply of water underground I have never disputed but the conditions do not exist that allows of obtaining the large quantity specified byMr Corkill in his estimated consumption by pumping; unless the wells and pumping units are well distributed and not overtaxed. The question of operating costs plus capital charges of providing the quantity of water renuired now, and in the early future must make the cost per 1000 gallons fairly expensive. If the water could be pumped direct into the supply mains from the various wells without first having to be treated through some form of mechanical filter and thence into reservoirs and finally pumped to the tower for distribution the position would be quite different. Unfortunately this cannot be done. Again in reviewing the. overall charges pumping versus gravitation, ’ the heavy annual costs incurred in renewing house service pipes under the present system of supply, although not shown as a charge against the underground supply in the balance sheet, must not be overlooked as this;

expense has to be borne by the ratepayer. This cost and inconvencience would be reduced to the minimum with water from the upland source. Assuming that it is definitely decided to adopt a pumping scheme more or less permanently (if such a decision is possible) it may be advisable to look further afield for a source of supply which on investigation would permit of installing at one pumping station plant equal to doing the whole of the pumping necessary in one operation. If such were possible it would pay to have a fairly long pumping main. This is only a suggestion which may probably have already been considered.

Visiting the pumping station lately I noted the changes since I was last there. I would suggest that Mr Corkill’s recommendation regarding installing standby plant be acted upon as early as possible. Quite apart from the electric power failing the present total combined plant has only a capacity barelv sufficient to meet the combined draw off that will occur if a large fire takes place during a period of maximum draw off, or at a time when many service pipes are burst following a heavy frost.

Tn conclusion I consider that no matter which scheme is adopted, or pumping, the capital cost must be heavy, if proper provision is to be made to meet the requirements of the borough for a number of years to come. Invercargill at the present time is only one of of many towns now faced with the problem of increasing their water supply. I see no reason. -with the past and present information available why a satisfactory scheme should not eventuate.

Water we know is available from both sources providing proper precautions are taken in harnessing same. It now remains by working out the capital costs of the one scheme and the capital and operating costs of the other which is to be the cheaper per 1000 gallons of water delivered, ready for distribution, through the town mains at a definite pressure and in quantity to meet requirements over the given periods specified by Mr Corkill in his report.

As previously mentioned I will forward Mr Corkill any records that I have bearing on the subject that may assist him in finalizing on a sound scheme, whether it -be by pumping or gravitation.