TOWN WATER SUPPLY.

Poverty Bay Herald, Volume XLII, Issue 13700, 2 June 1915, Page 9

TOWN WATER SUPPLY.

MR METCALFE f S IJEPUKT. NEW- AUXILIARY SUPPLY AT TE ARAI.

An important report respecting the town water supply from Mi' H. H. Metcalfe was laid before a. committee of the Borough Council last evening as follows :— His Worship the Mayor, * Gisborne. Youi- instructions to report whether lull advantage is being obtained from the present arrangement nt Te Arai and whether any additional supply can be brought m:" The existing 9in. pipe brings all the water m the creek at the intake during the dryest time when the flow at that point, according to measurements made la-st summer- is only 450,000 gallons, a da.y, while the maximum, weekly draugit before the hoses were stopped was over six millions. . • The Venturi meter shows the hourly -draught to vary from 70,000 to 15,000 gallons which the 15in. pipe supplies, but the meter having been put m the M-roug -place (near the tank instead of just outside the town), the pressure maintained is not recorded. The settling tank is not arranged to the best advantages, m a tank acting continuously, the ouxlet should obviously be as far from the. inlet as possible, and the original drawing shows it thus, but ;is carried out the inlet a<nd outlet are dose together; a worse feature is that the inlet continually discharges the full quantity the pipe will carry, aiiy excess mi the draught passing out 'by theoverilow, much more mud is thus brought into the tank than need, be, especially : m time of flood. The inlet should bY ! controlled by a. ball valve which would shut off the supply when the tank is full, and admit only 'enough water to meet the demand. As now arranged, the tank is useful chiefly to store water at night when the draught is small and so provide for. a maximum draught m excess of the supply ; as a settling tank it is of little use. T,o alter the position of the outlet pipe would involve considerable trouble and expense and it might be left for the present, but ■ a 9in. ball valve should be fixed ou^ the inlet. The proposed settling tank seems unnecessary as .the addition of the ball valve will greatly increase the efficiency of- the present tank, the cost of which was, I, believe, £6700; another would cost as much and the money might be spent with better result on. the second clause of the question, bringing m more water. THE NEW SOURCE.

Jusl below the tank. Te Arai creek forks; the right branch seems nearly as bio- as the left one from «which the .supply is taken, but as its catchment aaeu is all cleared it will probably fall off m summer much more than the other, which rises m the standing bush. Following this right branch up about four miles it forks again into two nearly equal streams at a height of 450 ft. above the tank. On May 20th, a rainy day, this ■ stream was muddy, though the main creek was nearly clear. ])uring <iry weather this water is probably as good as the other, and allowing that it tails off considerauly more than the bush-covered stream, perhaps 200,000 gallons a day might be got from it at this point, above which no houses exist, the nearest dwelling being Mr D. Parker's, about 1£ miles below. The catchment area is cleared and grassed and makes a fair gathering 1 ground ; at the worst a mechanical, filter might be installed at the tank and the water passed through it. Some 60 chains down the creek and EOft. beloM r the fork is a lagoon about four acres m extent," 26ft. deep m the middle and 15ft. half a caain from the shore : this la^oqn is probably formed by a large slip blocking a former gully, but it has existed for many years and i.s more or less stable ; the water m it being merely the • rainfall on a> small catchment area affords r.x> source of supply. On the date of my visit there was ft small trickle running m, but no outflow, the pond not being quite full; when it is. it overflows to the creek by a small ruunel which has hot cut down m the first X) chains, showing that the stroam is small. It would, be possible to lead a pipe from the fork, which appears to be 50ft. higher and 60 chains distant, into this lagoon and utilise it as a storage reservoir from which a pipe might lead to the existing settling tank. Rooking at the character of the ground 1 should- not -care, without making an .examination by borings, to raise the water level to r any great extent; more than, say, sft, w bft. but assuming this was done and that an outlet was tixed, say, 15rW below the present water level. I estimate the storage thus obained might amount to 20 million gallons. Now, assuming t,at the flow of the creek during 100 days of dry weather was 200,0QQ gallons daily, this with the 20 millions stored, would give 4QO ? QOG gallons a day for the 100 days; 'which, with the 500,000 gallons which the other, branch yields, would give 9C0,000 gallons a. day through the dry weather. During wet weather, of course, over a million can be got from the; present source. Tins would be a comparatively inexpensive way of increasing the Te Arai supply, .The levels and distances would need verifying, the distances being merely estimated, and the levels from unchecked aneroid , readings, but on the levels and lengths assumed, three miles of 6in. pipe to the lagoon and one mile of Bin. pipe to the iork would deliver this water. > • The trench for the outlet pipe would be cut about 16ft. deep and would empty the lagoon to that depth, but it would be a small matter to by-pass the water frpm. the creek round the lagoon till that part was ready. A thorough examination of, the ground might justify raising the wate"r level still further, but tins cannot be reckoned on at present.. .No material for- concrete appears m t lie neighborhood and an earthern dam isa.ll; tliat could' be made.

Tb© cost of these pipe lines with the ndceasary work afc the lagoon woul<| probably amount to £7000. Or the creek might be picked up at a much lower level, a-boat 120 ft. above the reservoir, m three miles from the settling tank by an Bin. pipe at a- probable cost of £5000. • Either of these, with the present Te Arai supply would tide over the present shortage till more extensive works could oe introduced. THE PUMPING SOHE-ME. Regarding the second and larger question of providing a. supply for .m ultimate population of 30,000 with an immediate instalment equivalent 1.0 600, 0QQ gallons m 10 hours/ by pumping from Waipapa lliver. I examine 1 the banks of the pver op, both sides from the bridge pp tp Patutahi, having

m mind the iuibiliiy oi" this district lo occasional Hoods ot great magnitude. Without going a great distance away 1 these .'ioods must be put up with, ami liough some temporary :nconvenience must be expected, the demand at such times will Do at a minimum, nor w-j.'i Hie disturbance las'-- long.

■JLvoma cursory examination, the left bank of the river at <Vbou 15 chains above the railway bridge, near tlie boundary .of sections 16 and 24, seems the best place available; higher up the river might prove better as to floods, but the length nf main would be costly.

The liver bank 1-ere would be above any but exceptional Hoods; the distance t'uoin the town boundary by tho shortest- route is four miles. * For various reasons I do not think it advi3abk? to pump into the existing 15in. main, the risk of damage which would ' leave the town waterless is too great. In any case it is necessary when pumping into the service main direct to have an open end to it at an elevation corresponding to the pressure to be maintained, and if this open end is too tar away, as at Te Arai, the pressure m the mains may rise very high when the pumps are running -full speed. T.o pump on the large scale proposed, a new main to the town will be necessary with a standpipe or reservoir near the town. . To pump directly into the mains with cnly a small margin m a. standpipe a special type of machinery is needed Hie engine must be capable of rapid acceleration, as the di'aught suddenly iureases, and it must be able to run dead slow as the demand slacks off. These requirements can be met with steam, but ti> pump with the greatest economy a suction gas plant with slow-running pumps will be best, *and this class of engine must be run at .practically an even rate of speed, so that unless, a service reservoir of some size can be got, it would not be feasible to instal a. plant which can keep pace with the demand when pumping directly into the mains and art. the same' time form one unit of a- much larger plant as the Council desired. The lay-out of the pumping plant, thus turns on whether a service reservoir can or cannot be got. • ■ RESERVOIR SITE. Having failed to find a. suitable site near the town, I searched further, back and found a possible site at the head of a. valley near trig 107 on section 16, where there is a very fair site, but 100 ft. too high, but just below a. service reservoir of no great size might be set m the bottom* of the valley, the creek to be diverted alongside it. This site is four miles beyond the town boundary where the main enters, making a total length of eight miles nf main required by the shortest route. At present prices a cast iron' main to deliver 60.000 gallons an hour Would tost, laid with necessary valves and fittings close on £4000 per mile, say, £30,000 for the eight miles ; and a. steel pipe of useful thickness would cost nearly same ; the pumping and filtration plnnfe may be set down at £25,000, and the servioe reservoir — dependent on size — say, £5000, or £60,000 m all. Then, if this is to be part of a larger scheme, the question arises whether the main should not be capable of dealing with double this quantity to meet future requirements, which might add, say, 50 per cent, to its cost. It is clear that merely to' supplement the present supply by pumping into the service mains, a steani plant and new as' far as the town boundary- is required. This main, might run side the railway m an almost v direct line and might be of smaller dimensions, I2in. would serve, and the cost would be about £10,000, but \ a standpipe would be needed on the hill at .the end of Wi Pere Street, worth £3000, and mains to connect with it, say £2000. Roughly, this supplementary scheme would cost for the steam, pumping, and filtration plant £15,000, ' main £10,000, standpipe and connecting mains £5000 : or £50,000 m all. * At the present moment with, prices fluctuating and freights uncertain it. is useless to enter minutely into details, but these estimates may be taken as approximately correct. The case evidently ne"ed9 further consideration. If arrangements can be made to take the water on the right fork of Te Arai and utilise the lagoon it may be possible to defer the more expensive proposals for some time, during which further i investigations can be made. T have not myself had an opportunity of seeing the locality m the driest weather, and the falling off of the stream last summer is beyond what one would have expected. Yours faithfully, MENRY H. METCALFK. Auckland, May 29, 1915.

Consideration of the" report was held over until tho next meeting of the Council •