DUNEDIN CITY WATER SUPPLY.

Otago Witness, Issue 2317, 28 July 1898, Page 45

DUNEDIN CITY WATER SUPPLY.

No. 11.

In a report submitted to tha council lv May last Mr G. ML Barr makes four septate proposals as follow : —

A. "A direct draw-off from tbe Lfcith a short distanca above the inflow oi Nichoi's Creek, at a height of 540 ft above the city datum, whore it receives the rainfall of 3900 acre 3of ground."— The catchment from this area Mr Barr estimates, in a period or drought at 700,000 gallons per day,— an amount equal to supplying 11,000 people. A 12in pipe would be required to coavey the water into Ross Creek reservoir. This work is estimated to co&t L2COO ; and for quite a moderate additional outlay tha scheme could be extended to tbe next gully (Sohoo'.bouse Creek), "wbere storage to the extent of 50,000,000 gallons could be secured, ia addition to and quite independent of the present reservoir." The reservoir would require an embankment of 55ft in height. B. " A supply which will give to Dunedin fcoth increased quantity and procure upon the bigh parts." — The draw - off would be from the same point in the Ldth as in scheme A, with a clear head of 120 ft above tbe highest part of York place. A lOin pipe, capable of supplying 15,330 people, with a direct dvaw-rff from the Leith, would be taken down the Leiih Valley to Gaorge street; then aloi-g that street and up London street to Arthur stresX The cost of the above f-cberne would be L 4900. No draw-off from this supply would bo permissible in the low levels, al'bcugh some of the water might be used in tbe cross-streets coming downwards from Arthur street.

C. A combination of A and B so tb^t the present Roes Creek reservoir could be utilised for storage by having a 12in pipe down the Leith Valley and up to the reservoir, as in scheme A, taking a lOin pipe from the point where it leaves the road for the reservoir to Arthur street as in scheme E The cost o£ tbe combined rebemes would be L 5900.

i>. " Schemes for Dunedin and high suburbs."—The proposal is to "draw off from the Leith, 92Sfr. above city datum, or lS5 f t above trig. It , JMievu?, whore there i 3 a gathering area of 1(500 acres, and a daiiy flow in the driest seasons of 320,000 galloas, t qa3l to a popu'ation of of 5330 people." But this could be supplemented by a storage reservoir in Mount Cargill Creek, wbere there is a good site for such a purpose ; also by bringing; water across the saddle from the Waitati. As regards the reservoir in Monnt Cargill Creek, an embankment 41ft bigb would provide storage for 6:>,000,000 gallons, and the estimated cost is L 5400. This reservoir, together witb the ditect draw-f2>, would be sufficient for tho supply of 14,000 people By means of a» embankment 51ft high" 91,500,000 gallons CDuld be stored. The cost, would be 1^9300. and the supply supplemented by the direct drav?-cfr would be sufficient for 18,400 people. The draw-off from the Wait ati would lap tbe drainage of 2200 acres, and the catchment would equal 440,000 gallons, equtl to tbe supply of 7830 people- ; or united to the Leifti water tbe f-upp!y would be equ-il to tho requirements of 12.G60 people. Tbe wafer wcuW have to be btcught into tbo Leitb channel across the saddle from the Waitati, and would flow down to the intake at the high level. To convey the water across tbe eaddle 1^ miles of 9in stoneware pipes -would be required, and 60 chains of Sin iron pipes laid on a district road. The cort would be I/I GOO. A3 these pipes would cairy a great deal more than tbe rniniraum drought yield, opon whicb basis the calculations are made, ths surplus could be carried toweids the reservoir in the Leith. The Waitati supply could be further augmented by a storage reservoirat a height of 1088*1. capable of storing 52.000,000 gallon?, equ?l to the supply of 7200 people, at a cost of LSOOO.

If Mr Barr's proposals were carried out the available water supply from the various eources indicated above would be as follows : — Tbe direct draw ofi from the Leith •wonld satisfy the requirements of 5300, while the reservoir with 94,500,C00 gallons woold be Bufficient for 13,100 during a drought period of 120 days. The direct draw rff from the Waitati would supply 7300 people, and tbe 53,000.000 fraUcns in the reservoir would suffice for 7200 people. That would represent a supply in tims of severe drorght from tha high levels equal to the requirements oi: 32.900 pe0p1e. In addition, if the diaiuwge from 2300 acres between the low and high level'! of the L'ji'h supply is utilised there wculd be a supply without storage sufficient for 7GOO people, bunging the total supply available under Mr Barr's proposal;-, in a period of severe drought", up to the requirements of 40,500 people. Thic supply, Mr Barr point? on 1 ", could be still ftrt^r it-creased by the erccMon of a roeervoir in the Schoolbousa Creek, near Halfway Bush, cspable of holding Ho,oooiooo gallons; end the Ko;-s Creek reservoir of 50,000,000 gallons could be filled seven times a year from the Leith. The high level rfeervoir of 0-} 500.000 gallons could bs filled from the Lei'h a!oce 2;J times, or by tbe utiited Lsith and Wait?b 05 times a year, in addition to the direct draw off. The total cost of constructing two reservoirs — one of 94,500,000 gallons and another of 52,000.000 gallons— vritb the necessary connections, including second reservoirs for Roelyn and Mornington, Mr Barr estimates at L 25 415. This he apportions as follows: — Dunedin, L10.G95; high suburbs, L 11.420. He points out that tbo figures appiy to a scheme very greatly in excesß of present requiremtnts, co that a part of it might ba selected. Ha therefore suggests the following scheme for Daaedin:— A direct draw-off 'from the Leith a short distance above Nicbol'jj Creek into tbe Ross Creek reservoir. Thu would supply 7000 peop!e at a cost of L2OOO. A pipa from the high' reservoir to R<yal terrace, by way of Driv&x'a corner, M*<"ri Hill, would cost an additional L 5515. Piping from the Waitati would cost LI GOO, and a email reservoir a'; the Leith draw-off, holding a three days' supply, would cost L2OOO, making a total cost for the partial fcheme of L 11.115. The supply theicby gained would suffice for 20,200 people— from tbe Lower Leitb 7600, and from the Waitati and. Upper Leitb 12,600 peopte, The water

gathered from these source?, Mr B\ir sstp, would be coccapiioniiliy good, but it would ba well to allow L4OOO for Jii'.or b«d.«.

Me Bjrr'a estimates are for the enst of congtiuclioii only, no aecu-mfc bf-ii'g taken of the riparian righto that win have to be dealt with. In a separate report Mv Barr dsala with this matter. To bsgin with, ha says :— " The circumstances which occasionally give rise to valuable water rights are whsre that is used as a motive power and the substitution of any other would bo much more costly. The purely theoretic power which may be used, and is not used, counts for very little." On the Waitati, Mr Barr says, water power is not at present used ; and on the Lsith there are only two cases. One of these ie Steven's mill, tb.9 water right of which is derived from the Town Belt, of which the City Council is the proprietor. The other case where water power is used ia that of Davidson's saw mill and &tonecrosher. The compensation required for this wator right would not be a Urge amcuat, especially bs only a portion of the water would be abstracted. Bat ween \he points of draw-oil and Mr Davidson's intake there are large inflows into the Leitb, which would not be affected by Mr Barr's scheme. He further points out thai the Leith is used for general purposes by the paper mill at the inflow of the Schoolhouss creek; bat the withdrawal of the water be proposed would not prejudicially affect that industry. Anderson's mill was burned down some years ago, a»d has not since been restored. When this miil was in full operation " its rights V7ere offered to the corporation at a figure very small as compared lo what was assumed as thafr value in previous discussions of this nibject, which also would be farther reduced by the fact of the water not cow being lued." Over the remaining pads of the Leith, between the proposed high reservoir and the Town Belr, there is only a length of some 20 chains in which any water right could arise, as there is a road line between tho private lands and the stream. Mr Bait suggests ihat riparian proprietors might be dealt with as ia often done in Britain — by giving them a proportion of the impounded water. Allowing for that, owing to the large quantities obtainable froca the two watersheds, thero would sti)l ba plenty left for a much larger population than that of Duaedin and suburbs at the present time. Ia conclusion, he says : " Upon a full review of the circumstances I am confidant that the compensation n quired in the carrying out of ray proposal could not be so large aa to nullify, or even materially depreciate, the othir great advantages which could be obtained."

Iq connection wKh the estimated supply of water obtainable from the sources named by him, Mr Barr says the figures are founded upon the results of gauging done by himself in the droughts of 1886, 1891, arm? 1898, on the Leith at the intake of the proposed high level reservoir, at an elevation of 867f(. above sea leve}. The figures quoted by Mr B=irr are at, rates 20 psr cent. 1333 than the lowest gaugings by the City water deparfineofc in connection witb the Rjss Greek reservoir, and 33 per cent, less than the rats adopted by Mr George Gordon, M.1.0.E., chief engineer Victorian water supply, who r~poi!ed upon the W^itati gathering grouad in" 1576. Mr B avi-'s figuree also show the Effiuaut of rainfall gathered per acre lo bs less by a corresponding amount than the figures supplied to the Maori Hiii Borough Council in 1881 by Mr H. P. Higginson, M.I CX. Mr B-xrr has therefore laffc a safe margin, and apparently there is not the remotest chance of the supply, should Ms scheme be adopted, ever filing below his estimate. R portir.g upon Mr Barr's scheme. Mr Mirarns, ciiy surveyor, says "it is open to tha very grsat, if noi- fatal, objection that it involves the construction of a largo reservoir on a stream having direct, cominurncfction wi'h the city." Mr W. N. Blair in one of bis reports entertained tbe same view. He stated that " there is a serious objection to storing a large quantity of water ok the Leitb. The valley is straight and narrow, and leads right into the city at a considerable elevation above a densely populated part, consequently aDy acoidant to tho dam would be productive of calamitous results." Mr Mir&ms adds : " Stuca that report was written in 1877, such dispslreiH results have followed from the bmstirg of reservoirs that possibly legislative authority could not be obtained for the ona proposed." He further says that he has never considered the Lsitb as a permanent source of supply for the city. Ifc is open to the following objections :— Proximity to the city, and, consequently, liability to increasing" pollution as settlement and occupation advance. Danger of constructing reservoirs, which is intensified by our liability to earthquakes and the coat, of ex&ifiguißbing riparian rights. In. addition there is the disadvantage of depriving the Lsith in its CJHise through the city of such a large proportion of its present flow, which in dry weather would be certain to increase the bUtftizidioa which is ev&n now afc times appareot. Mr Mir&mg concludes his report by exprotsir-jj the opinion "that the question of additional supply would be best settled by the construction of tho reservoir s.t Whare Fla';, whatever ultimate steps might bs taken as respects the Leit'j."