THE HIGH-LEVEL SCHEME.

At (he meeting of the City Council last evening the joint report of -Mr K. Hay, of Dunedin, and Mr W. A. rimith, City Engineer, on the wall of the new reservoir'- and tho augmentation of the high levels vvater supply, was presented. The report, was as toUows : — BROOK STREAM RESERVOIR. "We have made a careful examination .f the concrete dam at the lower reservoir. The concrete work, foundation;, und connections with tha east and west spurs havo been opened up, and now at-foi-J a fair opportunity for inspecting the work. . . . "The da.-n wall at the west side has been built on the shelving rock which should have been stepped and levellc. before the concrete wai deposited, and the wall has not been -aimed tar enough into the spur,- so that it mig ht be keyed into the solid rock: At s the east end, the rock, which is of a soft nature, ha.*- been tongued into the <?**«*> whereas the concrete wall should ha\e\ been recessed into the mam rest, so as tc make an absolutely tight joint "At the time of cur first inspection the reservoir hud been drained and after the inside "of the wall had been viewed instructions were given to Ml U P "£ reservoir, in order to find «•*»* «®£ l hydrostatic pressure had on the concrete "The water rose in the reservoir to a deott of 9ft. 7iu. on the gauge, and at 'nis point the water did not rise any hkher? as the whole of the incoming stream then passed through or under the concrete, mainly where the plaster and exterior concrete had oeen removed in order that the quality of forming the dam might be determined. "In February last the leakage through the dam appeared to be on the increase, and your Engineer gauged tho actual'quantity of water that was cscap. iue from the reservoir through, lound, or under the dam wall to be a total quantity of 270..000, and there ««■*■»- Sin, into the reservoir b^OOC gal on* <o that, nearly one-half of the total inflow was lost thr-ugh leakage. •'Material.— Tho mawnal ot which the dam wall is somposod is an inferior con-.-rete, and its inferiority consist-, tint in the class of aggregate employed, the ...ton* used beinir unsuitable, trom its soft aud flaky nature. The coital 8 al**o porou«, on account ot the "iter 3tic.es not being filled with suitable fine material, such as clean, sharp sand, 01 fine gritty gravel. . "The concrete h.ifi also been irregularly mixed, and on being broken into pre. s'enls itself in various stages of solidity, but, generally speaking, there is little difficulty in breaking it out with an ordinary pick, and in places the broken meta'" could be taken out by hand and we need hardly point out that such material would be quite pervious to water undei pressure. . "Qoricreto composed ot a suitable agcresato, properly mixed under the usual conditions with the r.po-.ificd amount of cement, should be of such a hardness and solidity that it could only be cut ou„ by oads. . ... '"We may here states it is our opinion .hat had the work been carried out .11 the true and full meaning of the original specification, the present trouble would not have arisen. RECOMMKNDATION. "The cost of the work has been £J1 S7l, and it -eems to us very desirable that some scheme should be adopted whereby this large expenditure can no utilised, and we shall propose to your Council an expedient by which we hope to reduce the leakage to a minimum, or possibly entirely. "Our proposal is as follows :— that a face wall of 'oncrete shall bo built en the inside of th- dam, \arying in thi'kness from oft. at thi foundation "level to 18111 at, say, a helfeht of 10ft. above low water level, or about 23tt in height altogether at the deepest point of foundation. The base pf wall to bo carri-rl down to the solid rock in every instance, and in no case less than 18in. V.clow the present foundation The face of dam wall to be rough picked, to make a good joint with the new work, aim bond-, r-hall be made at frequent intervals with railway rails, let loin, into the present, wali, with turncd-up ends, the ifMsses beina Tiled up with fine concrete three of gravel to one of cement. The rails alM> to be bui:t into new work for a »ength of at least Iwo thirds of the thickness of the wall. "The concrete of new wall shall consist o f washed river gravel, with sufficient ant or sand to fill in all interstices, "and this :;c:sregate to bft used in the proportion of one e:-..-k of cement (rorfl.ind) ta cnctl cubic ya^a. °f "SF"*" ealo New will alsn to be plastered three-quarters of an inch thick, put on in two lavcrs, with cement mortar in ">e proportion of one of cement to 2 -f clean sham aa-id. The east and west ends of dam" wall to be extended into the solid snn-, and the new face wall ta b> stepped into tbe solid reck on tho inoida. ESTIMATE. "We have plotted a section of th 3 I proposed new work, and tak-?n out the 'qnantilies of woik and matori.il rfn.il if •>d, un 1 we estimate the cost at ±/<2<HH V,'e are of ooii.ion ih.it, if tha v.*ork is cnvi*.?d out iii the -tvle we recon.menl, Ihe dam will be materially vtrengthenad ai:d the leakage stopped. INCITRASED PRESSURE FOR HIGH LEVELS. "We have also looked into the question cf providing increased pics,-ure 111 the city water mains, iii order that the high levels of the city may be supplied with water undar sufficient pressure to be of service for fire extinguishing purposes, and we have examined the crctk for a, distai.ee of about 40 chains above the uppei* dam. "At a point about 30 chains up the creek there is an excellent sita for an intake, where a dam. say 20ft.- high, and abr.ut the same in length, can be built of r-übble masonry in cement, and a couple of days' water supply impound, ed, and an additional 120 ft. elevation above the upner dam be obtained. "We would recommend that, this small dam he constructed and the water conveyed by 9in. spiral steel pipes, and connected up to the- main, at the present upper reservoir. "In this way about 501bs. additional pressure will be obtained on the high levels, and an uninterrupted flow ensured for fire and domestic purposes. The 'portion of the main between the upper and lower reservoirs that now consists of 7-in. pipes will have to be rcnlaccd with 9-m. c.i. pipes, which wilt be connected up to the 12m. main at the "A 12in. reflux valve will be fitted here and a 9in.- reflux at the upper reservoir. By this means when the hiju pressure "supply was exhausted, tne present upper reservoir would then auto- , matically supply the town, and in the event of this reservoir being emptied the lower reservoir would then take up the supply, until the higher reservoirs became replenished. "The cost of the proposed small dam wall and 30 chains of steel piping, laying and jointing, also lifting and replacing the 7in. main with 9in. c.i. pipes will amount to .-SBSO. "Some of the fittings and pipes are in stock, and can be utilised accordingly. "If our recommendations are carried out, the total expenditiurc for restoring the Brook dam, and providing increased pressure for the high levels will be £3268, and we feel sure that the city will then have an adequate return from the Urge expenditure that has already been incurred on the city water works. "We have the honour to be Sir, "Yours obediently, "R. HAY, "M. Inst. CE. "W. ATCHESON SMITH, "M.A., B.Sc, M. Inst., C.E., "City Engineer." The Mayor said that the. report was a very damaging one. and he moved that, it be referred to next Friday's meeting. Seconded by Cr. L'ightband, and carried.