BOROUGH WATER

Gisborne Times, Volume LXXII, Issue 11592, 19 August 1931, Page 5

BOROUGH WATER

ENGINEER’S NEW SCHEME

RESERVOIR Ay, WAIHIKEre

insurance. Raying - an* < TICIPATE3>

COUNCIL, APPROVES CIPLE)' •• -S '-i ■£?

Unanimous approval was*, expressed by members ... of. tho; VBbroiigh Council at last evening’s ' meeting: of a proposal, by tbe engineer Jlr George Darton, for the construction of a storage reservoir., with a cabaeity of from 80,000,000 to 100,000UK) gallons, .at Wfeihirere, the V'ore "fo be ejarried out under the unemployment- ‘Board's k V No. V 5 scheme. To complete the project it ? will bo necessary to raise a loan at some future time, this being to defray the cost of a pipe-line, ostim,at^^]VJ^,l>arto^’at a minimum <of £20,000. The effect of the scheme It IS considered, would be to bring about a re-classification of the-:tpwn for insurance purposes which would mean a very substantial saving to 'residents. The council’s approval Hast evening was merely of the principle of . the proposal and the actufal construction is a matter for .future consideration, after consul-, tation with the insurance underwriters and the local Officer -of Health. A fortnight ago, the engineer briefly sported on his plans to the council und then, last evening, ho submitted fuller details in, a special report which .was briefly discussed by councilors and then adopted. •Mr Darton’s special .Tcport was as follows: “Boluro arriving ait a solution uf the augmentation supply it is necessary to review existing conditions. Ju the winter, or in a weti season, Aral watershed can supply our requirements many times over, but m n dry season the supply falls to about half- a million gals. Tins is not •sufficient for our requirements and lias to be supplemented by pumping from Mangapoike. If we could always rely on getting enough water from Alangapoik e -to supply Arai’s deficiency wo .would ho fairly safe, but the true position is that when Aral “goes dry’ Mangapoike -goes •dry’ also. We had the experience, last year, that for weeks we required to secure every drop of water in the Aral and Mangapoike Valleys to meet our requirements. The greatest jiossible economy was exercised and yet on several occasions we only had a few feet of water left in the reservoir at Waingake. A slight shower, first ou Mangapoike watershed and subsequently another on Arai watershed, enabled u>s to carry oil.

‘Tt is proved beyond all doubt that hi a dry season the combined supply of Arai and Mangapoike is sufficient to supply our requirements aud it is, therefore, obvious that the supply must he augmented. This could only be achieved, (if by an auxiliary supply, or (2) by storing sufficient water to carry us through. a dry season. . "‘Dealing with (1). auxiliary suplily: The country adjoining Gisborne has now been cleared of busli and is "open for inspection’ and within a 80-mile radius there is no watershed that can furnish a suitable auxiliary supply by gravitation. To go beyond a 80-mile radius the cost to my mind would bo prohibitive and quite outride our means. Water at low levels «:ould be obtained from our rivers hut the quality is that cveu by artificial moans it could not be rendered fit for a town supply. NO SUITABLE UNDER GEO UNO L SOURCE. . “To obtain sufficient water from underground 'sources is always very problematical: aud the most careful investigation lias failed to disclose 4 an underground source of sufficient X quantity or quality that would warrant the large outlay necessary. R must be also borne in mind that any water taken from the lower levels would be subject to an annual pumping charge—this could never be less than £IOOO per annum and probably very much more according to the amount of water required. 1 have. Bike all my predecessors, failed find a suitable gravitation, auxiliary supply within a reasonable distance from Gisorne. The only alternative we have, therefore, is to conserve sufficient water to carry us over a drought period., “As far as quantity uf water is concerned this is a simple matter, for we have, lor at feast nine months of the year, plenty of water running to waste. The storage oi I Ins water is a less simple proposition. To stort> this water on a low level site would .necessitate pumping which must be avoided if possible. I have, therefore, made a very careful 'search for a suitable .site at the necessary elevation where we could store a three months’ water supply lliat could bo delivered by gravitation !o our town reticulation at a pressure of not less than lOGlbs. The council have already considered a site for this storage basin at a point a little below the lieadworks at 'lb Arai.' ON 'QUAKE FAULT LINE. ‘‘This locality is on the earthquake fault line and on February 3rd-and ( ever since" has been subject, to more . ' earth tremors than any other part of our district. Repeatedly tho chimneys in this area have been rebuilt and at ladMhuy have been replaced by iron Quite close to the site of the proposed storage hasiu a largo slip carnet down last month carrying Away the pipe Hue. the yhoitf country has been severely shaken and; for this reason alone, it would not be safe to attempt to dam a large body of water in. this locality. The pipe line to Gisborne would be 22 miles long, half of which must be considered a very unsafe line. As l’ar down as tho Keay Station it is impossible to select what could bq called a safe line. “With a safe three months’ supply connected with pipes on a safe line we would not have to worry about this as wo would be independent of Arai water for the time being and have ample time to repair the most extensive damage. With ,such a .security any’ leaks on our pipe line could he repaired and our present pipe line could bo made to last" lbr many years yet. “The. storage basin would need to be connected to our reticulation by cast iron or steel pipes on- a truly safe line. The nearer to Gisborne for such a site the better, us even a 12m pipe will cost £2500 per mile. BEST SITE AVAILABLE.

' *‘The most? isriitable site that i call find for such a storage basin is at Waihirero Valley. It is 63 miles from 'Gisborne, but I cannot find one nearer. Probably no spot in Gisborne lias . been' the subject of more reports and controversy than Waihirerc but I would like to point out that the controversy lias been mainly on the score of its : ability- as all auxiliary supply. It lias been claimed, and 1 think rightly so, that the area of the watershed -,'is too small for ; a town supply or . even for an auxiliary supply. I do not consider it. from either standpoint. I ask you only to consider it from the standpoint of a holding basin. If we cap conserve there enough water for three months of drought I feel siiro our . water .troubles Will be over/'for ipany. years to come. ' ' The pipe line would be 6 milps 66 chains long, on a perfectly safe line the whole way. * The elevation is such that by gravitation it ' would fill the balancing tank bn Willan’s Kill .'from which, we can main-' Kina'tmiform'nressurs of lOOlhs.: , , -■• - .

extent of watershed

It lias a watershed above the proposed dam of c 66 acres. Six inches of rainfall on this area would *** lt o-„ over 100 million gallons; of water and evep. allowing ror .only, 30 per pent, of the water to creek, it would only take of rainfall to fill the holding . basin. That the holding basin would be filled in a .very (.short time. is obyipus.- Frbm care.fui observations extending over, many years, I am cop-' y inped. that tho re is , ample water to kqep tho. basin filled and circulated. , “Doubts' hayq .been cast on;. tho ability of the ground to hold water apd its 'stability as a dam site but on the. other hand eminent engineers like Messrs.- -. Mostayor, Merchant, Munroe WilsQii-. and .J. A. MacDonald have, reported favorably on its suitability for such a purpose, from the tests already made and from my own observations, I have' not tho slightest doubt as to the suitability of tlio ground for n dam site ami a holding basin, but in. order to remove any possible doubt in tho': minds of the council, or. of the xatQ-i payers, I would recommend, beforo any decision is arrived at, a thorough test of the dam silo and holding basin bo mudo. . Personally l have no doubt whatever as to the result. CONSTRUCTION OF DAM. v

“The dam itself could he ted either in concrete with a curvo upstream and abutments let well into the sides of the hill, or it could be made of earth as is commonly done. Before completing the plans of the dam itself I would like to dis cuss this point with the council. H constructed as an, earth Jam tlio whole of it could he dene with Scheme 5 labor and the expense would be very little indeed. The real expense of the scheme would be the pipes which, even for a I2in. pipe, would amount to nearly £20,000 aud would require to be the subject of a loan' when tho time w suitable.

“Regarding the quality of the water, the Government Analyst gives an excellent report. “From tile- geological map of the district you will see that " the country is limestone on a sandstone bottom. Unlike Te Arai the Wailiirero watershed is free from fault lines aud there are no slips whatever. Even in flood time the water is free of silt and there would be no danger of the basin silting up as in the Arai Valley.

PRESSURE OF 1001 bs. ASSURED. “Tho, main to connect Arai supply with Willan’s Hill tank is now being laid and is nearing completion. With thq completion of the balancing tank there will always bo available ample water for fire-fighting purposes at (lOOlbs. pressure. This L a second arm for the Fire Brigaot and it should result in a reduction ut our fire insurance premium-.. “The question of placing small earthquake-proof tanks • of water in various parts of the borough, quite indepeudeut of our reticulation, would giro us another arm for firefighting purposes and should constitute Gisborne as a first-class risk. The cost would not be great and the saving in insurance should be very considerable. This point should be discussed with the underwriters. “The completed scheme provides for connecting Waihircre reservoir with Willan’s hill balancing tank and also with the town reticulatiou and also with the Arai supply- main at Lytton road.’ As soon as the Wailiirerc reservoir holding a three months’ supply is completed and connected up we could dispense with pumping from Mau.ga.poik'o. J here is a great deal of work that could bo done under Scheme 5. This would riot only find useful employment for a large number of men hut it would reduce the amount of tho loan that will require to be taken at a later dale.”

HEADWORDS INSPECTION

REPORT OF THE COAIMITTEE

Tho waterworks committee present, ed the following report detailing .tile visit to the lieadworks on I riday last:—

“Your . coinmitteo have to report that a visit of inspection was mado in connection with the operations oi the waterworks, the. first place visited being the reservoir at AVaingake. The water appeared to be very clear and a largo quantity was .running to waste through the overflow p'P f3 - The journey was then continued to Alangapoike to tin; pumping [Station, the source of the summer auxiliary supply, when everything was in satisfactory condition. The caretaker, Air. AVykes, is to bo complimented lor tho careful attention bestowed upon this important branch of tlio council’s activities. “On the return journey thq A'enturi meter was. inspected and it 114* interesting to note the recordings made on the sheet by th 0 various earthquakes experienced. ‘‘The next locality investigated was AVuiliirere, when the creek was traversed as far up as the falls, where an ideal site for a dam is available, and your committee were impressed with its suitability. “Passing the Hospital Farm a call was made at the works proceeding under Scheme 5 in connection wiLi the formation of a roadway up Taumata Hill for the purpose of transporting materials to be used in thq construction of a small balancing reservoir which is contemplated to he installed in. this locality. Good progress is being made with tho laying of the 12in. C'.l. connecting mains between Lytton road and thq reservoir. The' pip<?s at present are being laid up the face of the hill.”

TE ARAI CHLORINATION

In a further report, the waterworks committee dealt with the suggested chlorination of Te Arai supply as follows: — “This question received your committee’s careful consideration, but a definite decision was not arrived at. Tho engineer reported that a representative of a reputable AA r ellington firm would bo passing through Gisborne next week when the matter ol a suitablo chlorinating plant, and other matters affecting tliq water supply generally, would be discussed and if possible a meeting with tho committee might be arranged.”

INS FRANCE CLASSIFICATION

OFFER FROAI UNDERAYRITERS

CLASS D WITHIN REACH

GOOD NEWS FOR INSURERS.

According to a lengthy letter from th<v general secretary of the Council of the Fire and Accident Undenvri 7 tens’ Association, which also came before the naeeting, the completion of the suggested - waterworks schemes wojulcl result in Gisborne being placed- in Class' C so ; far as .fire insurance, is concerned.' Even: the fi) Cullka'tjqii. of only a part'of tho'scheme would bring ' the town , within Class I). This would. mean a big saving ,in insurance premiums to. the town and will be very welcome news to insurers. . The underwriters’ letter opened with a . detailed survey of the position of Gisborne’s water supply and also . sought information on various pointy of ..suggested schemes. The letter, then proceeded.as follower “AwapuniTLagopp: With regard<to the Awapurii supply it is recognised that this js only an emergency .supply .to be used when the yield of the v V.

stream at Waingako. is insufficient to : meet domestic or. to provide a limited supply for sever flushing, qtc., in the event of tho main delivery . pipe failing. “As the yield of the lagoon over a dry weather period is an unknown quantity, it cannot he reckoned upon : to -any -great, extent Trom a fire fighting point of view. This would' depend upon the capacity of the pumps aud the head against which tliev would operate.- 'lt is considered that ; -in thq event of the main delivery. • pip© from the service reservoir at' Wiaingako failing, and the whole of the supply to i .thy town depending upon the water from the iAwapuni lagoon, it would not ho an economical proposition to put ‘in heavy duty pumps of large capacity to quell a possible heavy outjhreak of fire and to supply the quantity for domestic requirements, assuming tho water for the latter .purpose was suitable from • j the Health Department’s point of view. “The lagooii could be drawn upon for a few hour-.;, hut the time that may bo required to repair a break in th 0 delivery main greatly exceed the time for which supplies could be drawn from the lagoon. The yield of the lagoon is, as above stated, an unknown quantity, and -it may for a few hours give what your borough engineer estimates, but if continual pumping for several hours per day on end were carried out, it is considered that the country in the vicinity would be drained and the •supply would practically cease. “Ito Service Reservoir at Wiliams Hill: With regard to this proposal it is noted that the reservoir would be at elevation 260 feet above town’s datum and that the length of the !2in. main from tlxe, point of embranchment of the existing loin, plain is 7741 feet. The elevation at the point of embranchment is given by tho borough engineer at 270 ft. above town’s datum, but the distance from "this point to where the town's reticulatpon commences is not given. ■‘The proposed reservoir, when full, is to be floating oil the town’s j inains. From same, it is understood that the existing loin, delivery main frill still bo connected to the" town’s reticulation and that if the discharg. ing capacity of the loin, main is greater than the draw off at any time, the excess water will be discharged iiito the service reservoir and stored until such times a.s the draw off exceeds the discharging capacity of the loin, delivery main and then the service reservoir would come 'into action and provide the extra quantity required. '‘Owing to the exact position of the point of cinbrauehmont not being given and its distance from the town’s reticulation and also from the reservoir, wo cannot calculate the discharges to tho town, or to the service reservoir, witli any great degree. of accuracy, but from the information supplied it is considered that the pie/xmietric height must be at an elevation greater, than flic elevation of the proposed service reservoir before water could cuter ‘lie latter. It. is considered that the residual pressure in the town’s mains would require to be about lldlbs per tjquare inch before approximately 27U gallons per minute would enter the service, while about 380 gallons was passing on to the town at the same time. . “The above would b ( > subject lo slight correction upon receipt of exact data from you iri connection with the position of the point of embranchment of the JL’iiis. main. The discharge to the service reservoir depends entirely upon the draw olf from the town’s maims. Assuming that Lho . service. reservoir, was full, - the combined discharges of tlq. 12in. 1 in aim and tho ldm. main delivery pipe line' would give ‘ approximately 200 g.p.m. with a residual, pressure in the mains of about GOJbs per sq. inch. i “The question arises us to how your council proposes to keep the service reservoir filled, or a reserve supply of 000.000 gallons. The night flow into the service reservoir would be small, this, depending, as above stated, upon the draw-oil.. My council raises no obstacle to the construe, tiou of the proposed reservoir, but , they arc concerned as to what method ypu will 'adopt, to keep it fall. “As the proposed reservoir will be floating oil the town’s mains, and as you intend continually to store 500.000 gallons for fire purposes, it is assumed that when the level oi the water in the reservoir fell to this point, the outlet valve would be float controlled (electrically) to prevent tho reservoir ' being drained ; th 0 valve to be opened electrically or by other means in the event of a fire taking place. Is it your council’s intention ?o install the necessary pumps at the Awapimi lagoon to assist in keeping the service reservoir full P

“My council, after a careful perusal of the whole of the correspondence in connection, with the water supply scheme will as an inducement t'o your council to improve tin existing conditions, be prepared to re-classify the town if the following bo given effect to, viz.:—

‘‘Class D: The relocating and reconditioning of th c 4| miles of delivery main at present laid from tho,Wa injja be reservoir towards the town, wliich is at present in a precarious condition and badly located. The construction of the one million-gallon.- service reservoir at Willan’.s t- Hill, provided that this reservoir*.cim be kept filled or with a minimum reserve of 500.000 gallons for fire-fighting purposes. The installation of pumping machinery at Awapuni lagoon to assist in keeping the service tank filled. ‘‘Class C: This is the majoi scheme and consists of either of the two methods of storage and .supply as set out below: “(1) Hie construction of a fit 000,(lOO-gallon storage basin, or such quantity that would tide the town over the period ‘ when the

yield of the streams fell below the quantity for domestic requirements, due allowance being made for .seepage, evaporation, etc. The elevation of the storage basin to be at least at 265 ft. or greater if a- suitable ■site can be obtained so that the proposed -service reservoir at Willan’s Hill Can he kept filled; tlie replacing of the main with pipe of larger diameter, from Waiiigake to the junction of the town’s reticulation; pipe line to be at least 18 inches in diameter; the placing of tho Venturi meter at or near the town boundary and the installation of weir .recording apparatus at Waingake reservoir. _ The construction of the service, reservoir of 1,000,000 gallons capacity at Willan’s Hill as set out under Class D.

“(2) The construction of the G0,000,'000/gajlou .storage reservoir ou the Flats, which would ho a low head development; the

re-laying to the main delivery \ pipe from Waiugako to the basin i with pipes; of larger diameter, j The installation of high , lift turbo. pumps of sufficient capacity to furnish the necessary, fire

streams and the quantity required for domestic requirements. .Thp, residual pressures ..in . th*. town, to he. such that fire hoses can bo directly coupled to the mains and not have to depend upon the firq engines to .boost (ho pressure. The pumps to bo in duplicate, electrically driven, and automatically controlled. The construction of the service reservoir at Wilkin’s Hill, as «©t out above. The electric pumps to operate at such a head that the service reservoir can be filled, ",

“Under Classification 0 it is assumed that tho pumping plant will be installed at Awapuni lagoon to provide a temporary supply in the event of the main between the town and the storage basin failing or being cut off for u short length of time.”

COUNCILLORS’ VIEWS

The various reports dealing with tho waterworks wore considered by the council together. The Mayor (Mr. D. W. Coleman) said that, when Ur. Turbott heard the engineer’s new scheme, lie rang up the speaker and said that he was very pleased with the proposals. The doctor mentioned that it was imma-

terial to him where tho, storage, reservoir was situated, but bad asked that, before the council did anything definite in the matter, he should be given an opportunity of testing the water and then of conferring with the council. This had appeared only reasonable aiid the Mayor had agreed with the suggestion. . Councillors commented that before anything definite was done in the matter, tho opinion of an engineering expert should be obtained as to the 'Suitability of the ground in the way of holding the water. Tho Mayor commented that the Loans Board would certainly insist on this step and went on to say that tho big point to decide was the 'System to be adopted, whether it .should ho a concrete dam or mudbauks. Cr. W. Cave referred to the danger of earthquake damage at Tc Arai ;and pointed out that, apart from this, there was tho danger of the lonp; pipe-line. It was obviously a better policy to have the reservoir at this end and Waihirerc seemed the most suitable point. Other important matters for consideration were . tho questions of the suitability of the Water and the extent of the evaporation. Cr. (I. Bradley Smith contended that, before carrying op. with tfio proposals, the council should first find out exactly what saving would be ioccasijoncd i.n insurance rates. It would be ridiculous to carry out 'a great dealt of work under flic No. b scheme and then find themselves im. able to carry out the scheme in its entirety. He. would lik e to know what the interest and sinking fund would be on the loan, required, and how this would, compare with the saving .in insurance. It would be useless to attempt to reach any finality until advice as . to tho saving had been received from the undo* writers.

Tho Mayor commented that all tho council could do that evening would bo to affirm tho principle of the suggestions.

, Cr. A. S. Muir inquired whethei *jho precarious ipipe-1 file would be able to stand up to the extra backpressure occasioned by the increased head of water.

Tbp engineer explained that the pressure in the pipes would actually be less under the new scheme than it was under the old system, foi there would be free egress at tjie end instead of a dead end as at nreisont.

, The Mayor mentioned that Mr. Fox, engineer to the' Underwriters' Association, was in •Gisborne and intended to look into tlie position, jto ■suggested that the council should meet Mr. Fox and go into the whole matter with him. This idea was supported by other councillors. The engineer’s isclieme was then approved unanimously, and it was decided to meet Mr. .Fox on Friday evening, also "that Dr. Turbott be asked_ to confer with the waterworks committee on the • proposals. Thp engineer said that he had -oven a great deal of attention to die matter of the borough water supply and that he would warmly welcome any suggestions whatsoever and also >any independent advice which the council desired to obtain. The reports were then adopted.