SEWERAGE AND STORMWATER.

Evening Star, Issue 12767, 21 March 1906, Page 8

SEWERAGE AND STORMWATER.

THE DRAINAGE ENGINEER'S v .'.... report. -■": : -.-.■;/■ At last night's meeting of tb? Drainage Board the engineer's report, ixistported from last meeting, was partially'discussed.' Mr Small said that they, had .at the .present tLmo three reports from the engineer which had not been disposed of. These were —(l) A report on the work done for the year ended- December 31, 1905; (2) a report on certain modifications and alterations to the scheme as originally laid down; (3) a report in relation to the disposal of the storm water within the drainage- district. They were, he'thought, in a position to discuss the 1 first two of these, but with regard to the. third, as the engineer had not yet been able to place before the Board all the information necessary to enable them to deal with it, its consideration would, he was afraid, have to stand over. The matters dealt with in the annual report were not of particular moment —none of them involved a departure from any policy adopted by the Board. They were, with one or two exceptions, mere references to the extent, cost, ox method of execution of the works. These matters had been referred to so often that to .discuss them further would lead to no useful result. They might also put aside for the present the storm-water question, because, as he had said, this was more fully dealt with in the third report. Nor was more than a word or two necessary on the point raised in the annual report respecting an adequate water supply for those living in the suburbs who were not yet in possession of permanent supply. It \ was obvious that until this matter was put on a satisfactory basis it would not be, to the interests of either the Board or the suburbs to do any ieti eolation where it could be put to an immediate use. The remaining items that called for passing comment might be briefly referred to. In Appendix No. 11. satisfaction was expressed that the Diesel engines had, ft their nominal load of 115 b.h.p., developed 150 i.h.p. each, and' proved themselves capable of developing a , 50 per cent, overload. While this was satisfactory as far. as it went, it was, he thought, a pity that engines were ordered of so low a nominal horse-power, and so far below the capacity of the pumps. If such a practice did not result in a break-down, ; it would tend to shorten the life of the engines. In Appendix No. ILL the rainfall of the district was dealt with. Tho j rainfall for certain years and calendar j months was given and compared. This treatment of the question was too general. They were told that the sewers had been designed to provide for a flow equal to the whole of half an inch of rainfall on the catchment finding its way through the drain in one half-hour; consequently, what they wanted to know was the rainfall per hour, or, rather, tho heaviest rainfad during any one hour. He would suggest that, in add.tion to the information contained in the appendix, the Board be provided with this additional return. It was further stated that, in consequence of their being subjected to a pressure of four times the normal, a leakage was developed in certain parts of the rising main, also that the leakage had been cured, and that if, upon a further test (which it was proposed to make after the reinforced concrete recently laid had matured), any new leakage was shown, the reinforced concrete would be extended. He referred to this portion of the report for the purpose of pointing out that the Board had not come to any such conclusion as was there stated. It cost tho Board £7OO to put the last leak in order, and he ventured to express the hope that the Board would not again be caDed upon to deal with leakages in the rising main. With these few comments he Would pass on to notice one or two equally brief suggestions that arose out of the report on certain modifications of the original drainage scheme. He might mention for the information of the general public that the drainage district as originally planned . was divided into two parte, one of which was to be served with what was known as the combined system—i.e., the rain water and sewage to flow through the same drain—aud the other by the separate system—separate drains for the rain water and the sewage. In the scheme as first formulated - the combined system area comprised that portion of the district bounded on the north by the Water of Leith, on the cast by Castle street, from the up to Frederick street, Frederick street up to George street, George 6trcet and Princes street, from Frederick street to Manor place; on the south by Manor place, Maitland street, Stafford street, west of Maitland street to Alva street, Alva street to Serpentine avenue and Hawthorn road, up to the line of tho Dunedin and Kaikorai watershed, and by the line of the Dunedin and Kaikorai watershed from Hawthorn road to the Leith. But this original <area had already been added to by the inclusion of that portion of the north end of the City which lies between Dundas street on the north, Harbor on tlie east, Frederick street on the south, and Castle street on tho west; and that portion of the City bounded by Princes street south, Manor place, ind Maitland street. There had also been added the Caledonian Ground and the northern half of the block of ground lying between Macandrew, Cargill, Hillside, and Forbury roads. proposed modifications involved a yet further extension of the combined area. Mr Anderson advised that there be added that portion of the City bounded on the west by Princes street, the Octagon, and George street to Frederick street; on the north by Frederick street, .on'the east by Athol place and Cumberland street, and on the south by Rattray street. That there were advantages to be derived both by the Board and the individual ratepayer from this extension of the combined area is apparent; but there were certain formalities to be gone through and certain consents to be obtained before the Board could give effect to this- suggestion. This was a matter which might be referred to the Works Committee for report. While dealing with this report, he might mention a minor matter which he thought it well to put on a proper footing. Mr Anderson wrote: "It is now several months since the heavy floods filled the detritus tanks beyond the amount which the small water pipes available from the town water supply will break up, and consequently I requisitioned a Vogel pump to work the breaking-up nozzles. So far the requisition is in abeyance. The detritus tanks canndt be kept in good order without this, so no time should be lost in importing this pump." As it might be inferred from the above that the Board would be blamable if on opening the detritus tanks more material was found in them than the permanent appliances originally fixed for the purpose of cleaning out the tanks are capable of dealing with, he thought it right to say' that this pump was requisitioned for the purpose of cleaning the sewers, the ordering of it being delayed until the appointment of the maintenance foreman, and that the only reference to it in connection with cleaning out the tanks was contained in a report by Mr Anderson, dated August 23 last, as follows: —"I would mention that owing to the low pressure in the town mains we have not Deen able to properly flush out the Frederick street detritus tanks for some time. If it were for no other reason, I would consider that this dredge pump would be a wise provision for cleaning out the detritus tanks during, drought conditions when the town . supply is insufficient." Unfortunately, for some at least, drought conditions have not prevailed since the suggestion was made in the above report. They might, therefore, ' take it for granted that the necessity for using the pump had not yet arisen, and that the town supply had proved sufficient. Thfe'-e suggestions and explanations appeared to him to deal with the main points contained in the two first reports. For the already stated, consideration of the third report might be deferred to a future meeting. Mr Gore said that he had no. wish, to discuss the matter now, and would move that consideration be postponed. Mr Scott seconded Mr Gore's .motion. He thought the Board had made a"huge ' blunder in ever tooefemg storm watv.r. Their whole energies should have been con- • centrated on the sewage question, and storm ■water should havq* been Jeft till afterwards i The keynote of the whole drainage scheme ■was, as- stated by Mr' Anderson in one of his reports.' that jthe scheme was. from the start a general one, and "as flexible as circumstances would watraai. , ' Be though*

'that that had been the drawback. Had' the scheme been made hard and fast from the start, they would have known where I they were He thought, with Mr Gove, J that they should have more information ! before'they considered spending any more money on detains tanks. He had opposed these tanks. all along. He would like to know how.those at the foot of Frederick street were working.' They had never beard , the cost of running the engines. There' were a great many particulars required before they could arrive at it. The least said about the rising main the better, he thought. Mr Marlow thought consideration should not be postponed. As to the cost of the engines, he thought it would not be wiae to judge them too much by the cost at present. In a short time these would be working 2,000 hours a year instead of, as now, 200 hours. Actually the engines would then be working something near fuil time. There was no question that a mistake was made in not getting engines capable of working their pumps. The pumping in anything like heavy rainfall would be a serious item once they got the intercepting sewer a little further on. With regard to leaving the storm water alone, his own opinion w;is the opposite to that expressed by Mr Scott. He thought it waa a pity that any part was touched whare the Board were not prepared to deal with the whole question. The Board were constituted to give relief to the ratepayers, and it was hard to rate people and supply them with sower drains, and ■ then tell them there was a further cost to be met. The oidy economical way was to do both works at once, and give an efficient system for sewerage and storm water. Mr Arkle agreed with Mr Gore. It was too late now to raise the question of the importation of the engines at too low a power. Ho thought the engines were a good investment, and got more out of the oil than any other make. Mr Christie supported the motion. He suggested that the Board examine the detritus tanks at the foot of Frederick street. He, too, regretted that engines- had been gob of less capacity than the pumps thev had to work The Drainage Engineer, in explanation, said that it was an error to assume that the pumps were of larger capacity than the engines which drove them. The fact was that there were three pumps, and their combined capacity was the same a£ the capacity of the sewers that supplied th« station. So far, only two pumps had beersupplied with engines. When the third pump w;r* supplied with its motor it would be found that there would be no need to overdrive any of the engines. At the present moment, in fact, there was no such need. But the circumstances of a centrifugal pump were such that it admitted rf great flexibility. If the height the water was thrown were varied, it might be made to do three times as much work as it was designed to do. This meant that great discrimination must be used with the arrangements,' and if it were not for such features there would be no need for keeping a highly-qualified man at the pumping station. The fact that ho had boasted that the engines could, and were being, run at | 50 per cent, over the normal should not. be taken as meaning that the engines were j smaller than they were intended to be. It would have cost the same capital to have had two engines to do the same work as they were giving for three When they were running fairly continuously on sewerago the work, if a larger engine were got. would be more intermittent. A number of moderate-sized plants were better than one large one. On the question of the strength of the rising mains, there was no single feature of the scheme in which he took more pride than in them. Strains had been put on them of more than four times what they were designed for, and arrangements _were now being mad© to test them with a ''fairly steady strain. In future a lesser fluctuation of pressure would occur, owing to the air vessels which were being fixed. On the question of the detritus tanks, these had never yet been subjected to as high a pressure from the water mains of the town as they were entitled to, owing to the town mains being smaller than was assumed. Mr Gore pointed this out, but that- was long after thoy had been committed to them. The town pressure was found to be inadequate. The pump for this purpose which ha-d been asked for would cost £l3O. They had the engine to drive it, and this pump would supplement the pressure that th-3 town mains were incapable of supplying. Th» Engineer answered a number of questions, after which Mr Hancock said he understood that the motion was that the report be postponed, but it had been fully discussed. If Mr Gore moved that the report be received they might postpone the discussion to any date.

Mr Gore said that in moving his motion he had tried to avoid debatable' matter. As it was, some of the most important points in the rpport had not been touched on. He did not the matter discussed, for fear he should say something he might be sorry for. He was willing to alter his motion "to one that the report- be received. This was agreed to. A number of tenders .for supply of screenings and spalls, a spring-van service, reticulation of Musselburgh, etc., were referred to the secretary to schedule in proper form and bring before the Works Committee.