MOUNT IDA WATER SUPPLY.

Mount Ida Chronicle, Volume III, Issue 184, 13 September 1872, Page 6

MOUNT IDA WATER SUPPLY.

Mb. D. L. Simpson to Me. J. Blackktt.

Dunedin, 22nd July, 1872.

Sis, I have the honor to report upon the proposed scheme of Water Supply for the Mount Ida District, in so far as it relates to the Sludge Channel for drainage of tailings, and Supply of. Water for flushing purposes from the Kyeburn watershed.

My examination of the district, and surveys instituted hitherto, have been mainly confined to this section of the whole scheme, the result of which is contained in the drawings prepared and forwarded, comprising plan and section of Sludge Channel, longitudinal section of Flush Race, and sketch plan showing relative position and direction of channel and race, and giving other information which I considered would better elucidate the subject under consideration. I may premise by stating that the weather was extremely unfavorable during the concluding half of my survey operations, and in a great measure prevented me from acquiring information of a supplementary character useful to the scheme, such as the mode of operation of the St. Bathans Channel, and the general inclination of tail races ; but I believe that the merits of the contemplated works, in so far as the Sludge Channel is concerned, will be app&rcnfc from a glance at the longitudinal section, assuming fall to be the most important requisite.

Tlie present channel for discharge of tailings was opened by the Extended Company some time ago, and, as originally constructed, was in length a little over three miles, {lie discharging point being at two miles sixty-five cliains; but, in consequence of the absence of a proper discharge area, tlie tailings accumulate to such an extent as to interfere with, its proper working at the lower end, and although efforts have, and are now being made to keep this part of the channel open, it is evident that they must eventually prove abortive.

At the present discharge point—viz., two miles forty chains—the bed of the channel is considerably elevated above the original level of the ground, to the extent of four or five feet, and this will go on increasing as the tailings accumulate.

The proposed line of Sludge Channel, as shown by the red line on the plan, was determined upon as being the most direct, consistent with economy in construction ; and with a view to the Channel being made available for the drainage of tailings from the prospective workings along the bed of the gully, the bed level is closely j approximated to the depth required. I have shown the Channel to terminate at a point ten miles distant from Naseby, it being, in my opinion, the only part where there is an efficient discharging area, and where it may reasonably be expected that its proximity to the Taieri River will not cause any accumulation to be so formidable as to interfere with the satisfactory working of the Channel. The Branch Channel follows more or less the line of the bed of a small gully, now filled with tailings to the extent of ten or fifteen feet above the original level. It is necessary for the drainage of the contiguous workings that a communication should be opened with the Main Channel. It is more expedient that this should be done when it is understood that the present level of the tailings at peg No. 2 is three feet above the street it the intersection of Earn and Leven-streets, and this height may go on increasing, to the detriment of the township, unless the Branch is opened. The Branch Channel will have a fall of 190 feet per mile. The Main Channel commences with an

inclination of 1 in 44, terminating at the rate of 1 in 125, or 120 feet and 42'2 feet per mile respectively. .

The existing channel has an average fall, from peg O to termination, at two miles forty chains, of 88 feet per mile. The sectional area, when workings are in full operation, is 5 square feet'; the mean velocity, 492 feet per minute ; and, consequently, discharge about 2,500 cubic feet per minute, equal to twenty-seven Government heads.

According to the proposed form of new Channel (see cross section) the sectional area is twenty-eight square feet, and hydraulic mean depth. two feet. Taking the full sectional area as representing the flow in floods, the mean velocity will be, at the discharging point, 715 feet per minute; and discharge, 20,020 cubic feet per minute. Again, assuming that the ordinary flow will be 100 Government heads to 9,200 cubic feet per minute, the depth of section at the point of discharge will be represented by about 26 inches; the sectional area will therefore be 15*7 square feet, and hydraulic mean depth I*4 feet, and accordingly the mean velocity Will be close upon 600 feet per minute, equal to 10 feet per second, as against 8.2 feet per second, the present velocity of discharge of "existing channel. The present channel has the following defects : 1. It is irregular in cross sections, j thereby increasing the friction and reducing the mean velocity^' 2. The supply of water in the shape oi tailings is intermittent, causing the gravel and sand to cake, which is afterwards difficult to remove, and consequently leaves the bed irregular in fall. i

3. There is no proper area to receive the tailings ; lience the velocity of discharge is lessened, and the tailings deposited in bed of . channel.

Notwithstanding the two first defects, repeated observations have proved that the channel acts its part well i'or the first mile and a half.

In the appended estimated cost of the, work, I have provided for the Channel' being pitched on the bed and partly up the sides. This plan, I think, should be adopted, in order that a smooth anct uniform surface should be presented to the tail water in its course. The extra expense of construction would be more than' counterbalanced by the saving in maintenance in a few years.

In my remarks upon the proposed Sludge Channel, I have assumed that there will be a constant flow of at least 100 Government heads, and I' think this may fairly be looked upon as the minimum quantity, if the Channel is to perform its functions and be useful in the farther development of the district as a medium for the discharge of tailings. I have gradiented a course for a Flush Race, commencing at the level of peg O, and following the contour of the hill slopes to the Little Kyeburn. The section shows the fall for the first, two and three-quarter miles to be at. the rate of 11*2 feet per mile, and for the remaining distance at the rate of B*B feet per mile, with a break in level at the crossing of the Stranraer Hill Range of 61.17 feet, this height being equal to what. I considered would be absorbed in following the contour line shown by red dotted line. The difference in level between the junction at Kyeburn and peg O at Naseby is 276 feet, the terminating peg 26-22, on west bank of Kyeburn, being twenty-eight feet above creek.

The line, as laid off, is very circuitous, the distance in a straight, line not exceeding seven miles, which gives a proportion of 1 to 3f; but this proportion is considferably less thaii would have been the case had tunnels not been adopted. The

actual contour "would have resulted in a totaj distance of forty-five miles, and the difference in level; increased to ninety fleet. ' ' ■ ;; •

The ground is all good, , and favorable for construction, with 'the exception' of about one. mile, part of which distance is in the approach to and from Deep Creek, and part in close proximity to the junction with Little Eyeburn. The from external appearances, will be through cement-gravel, and will riot be a very expensive operation.

- The dotted. lines on sketch plan; show, the course the race would halve taken had tunnelling not been resorted to. Between Milkman's Gully and the Hogburri Ci*eek I have shown an alternative course, which would involve a tunnel half a mile long, but would otherwise be of considerable advantage iir reducing the total distance, conseque'Qtly the tion. ■; u

Tiie (Hfferefice in cost would he triflmg, and; on that- account the alternative course csfii feinployiiig any 1 additional Outlay should it subsequently he adopted. ; ! ' •••" !i ' ! - o: '-

I find that on guaging the. various streams met with in the course; only foiir (living out thg (Little Eyeburn), afford a constant suppl^—-viz.;-Deejj Creek/north branch p ofj same, Rlat Oreek,-; an<|. Burster ; Cteek—^the'' aggregate 1 supply fcois wnich. not exceed, in ordinary, seasons; six' Government heads of the Lit* tie:^ c At'lffie bf my last visit,, arid ' from periodical examination Government heads could be relied upon, nearly all Of winch consists of water from .Clark's Diggings at Mount Burster. to'ihe rates now in existence, and,which derive their supplies from the tributaries of ! -the Little 1 Kyeburn, this' combined supply they are entitled to wbuld be, ; according ! to tabulated statement on sketch plan, sixty-six Govern?: ment heads- 'but' the races, as cut, have only, a ; carrying capacity of about eighteen heads, hence the remaining 'numbet' granted, I. am, reliably . can be declared forfeited. The greatest portion of the supply from the Little Xyeburn tributaries is used in slmcirig iat'Surface tailings from which flow into,the present Sludge. Channel, so.: that nothing; would be gained by the purchase of the 1 easting! rights.'

The only course to be pursued would be to store up the flood waters of Deep Creek and the other Creeks in the line of the proposed race ; so that a constant supply of something like twelve to fifteen Government heads could be available when required for flushing. It is not necessary that there should be a constant now ot flush water into the channel. Its useful effects would be when the flow of ! tail' water was at a minimum," and this may be considered at from six p.m. until eight on the following morning^ The reservoir I propose, at two and is capable of-storing 600,000 cubic feet. This quantity, with the constant supply from feeding race, would admit of a considerably body of water being brought to bear upon the Channel at any time. . In the estimated cost of providing water for flushing I take it for granted that the only, permanent source of supply from the Kyeburn watershed will be by supplementing that ' obtained " from the creeks; and this can only be accomplished byf contracting <iams at' Deep' and' other creeks,, having a combined capacity of say 10,000,000 cubici feet; but although' giving an estimate of the cost of the works necessary in accordance with the views above enumerated, I dp not wish to .be understood as thoroughly approving of the Kyelßurn FlusK Scheme,^nbtlso much on account of the uncertainty of

supply, as the heavy cost the carrying out of the works will necessarily entail; • It mightprobablybe judicious to postpone consideration of the Kyeburn watershed supply until the survey is of country between' Naseby and the head" waters of the Mariuherikia (instructions • t° undertake which I' received'from the Honorable the Resident Minister some time ago), as 'it-'is very possible that a 1 good, and constant supply' might be ob- i taiiied froih tha.t r source ata cfost not much' ' in excess of that from the Eyeburn.' . The ! conclusions that I have ; arrived' at are these.: The Channel Scheme is, per-fectly-feasible, and, if carried out, willbe a Work of considerable utility, and cann6t fail; to be the means of advancing the'; interests of the district and extending its

resources. ; The ; Scheme of Water Supply from the Kyeburn is practicable;buf expensive," and I 'would therefore suggest deferring further consideration pf it until the Manuherikia watershed has been examined and reported upon. I have, &c., D. L. Simpson, 7 ' Civil Engineer. John Blackett, Esq., Assistant Engineer-in-Chief. 1 Estimated . Cost of . Cokstbucting a ' Flush Race feom Ijittle Ktebubn, . including Bams. "... ' Tunnelling (sectional,area 16 ■ square feet) 1*551 lineal yards, at 20s. per yard.. 1,551 0 0 Steep siding, with I tection where required,. ; . r 80 chains, at 80s. per r cli ain ... ... ... 320! o 0 Easy siding, 1,951$ chains, at ; 255. per chain ... ... 2,439 7 6 Reservoir, at 2 miles' 60 . chains, capable of storing 6.00,000 cubic feet4oo 0 0 Dam at Deep Creek, storage capacity 4,000,000 cubic feet,.. j ... , ... 1,200 0 0 Dam at north branch of Deep Creek, storage capacity ~ 3,000,000 cubic feet ... 1,000 0 0 Other Dams at Creeks,: capable of storing say 1,000,000 cubic feet ... 750 0 0 Storage and purifying Dam u at Xyeburn, capacity cubic feet ... 2,000 0 0 '. , . £9,660 '7 6, Estimated Cost of. Con stbuction, op j Main & Bbanch Sludge Channel^ Main Channel. ' s. d. Excavation, 141;200 enbic • • { y ar ds, at Is: per yiafd.. 7,060 ■■ 0 0 Rtching, : l7,6ClOcubic.yards,' ' ' 1 I*' at 15s. per yard 13,200 0 0 Sod Walling, 5,000 cubic yards, at ss. per yard.. 1,250 0 0; £21,510 0 0 Branch Channel. £ • g. d. Excavation, 7,200 cubic yards, at Is. per yard .. * 360 0. 0 Pitching, >420 cubic yards, v '<■ ; ;.. 315 O O Sod Walling, 120 cubic t yards, at ss. per yard .. 30 0 0 , . / , £705 0 0 Main Channel ... 21,510 0 0 Branph Channel... ... 705" 0. 0 Total for Sludge Channel... 22*215 0 6 Total for Flushing Race ... 9,660! 7 6 Total ... ... ... £31,875' 7 6