DRAINAGE BOARD.

Globe, Volume IX, Issue 1280, 26 April 1878, Page 3

DRAINAGE BOARD.

A meeting of the Christchurch District Drainage Board was held tins morning at the Board's offices, for the transaction of ordinary business. Present—Mr Harman (in the chair), Messrs J. V. Boss, A. Duncan, F. Hoobs, and Wright. The minutes of the last meeting were read and confirmed. MR. CABEUTHERS, Mr Hobbs asked if the Board had received any commu ication from Mr Carruthers relative to Mr Clark’s report. '1 he Chairman said he understood that a letter was on its way, but it had net reached the

engineer’s report. The following report from Mr C. Napier Bell was then read. April 26th, 1878. Complaints ha.vc been made about the state of the Heathcoto below Wilson’s bridge. I would propose to let another mile to tho same contractor to keep clear of weeds. I submit certain specifications for certain drams in the Avon district near Horseshoe Lake, which I would propose to let by contract, to be maintained and kept clean for one year. If this arrangement were satisfactory, other parts of the district might he let by contract if tbo Board approve of this manner of dealing with the work. Mr Baker, of St. Alban's, claims an amount of Jt's for loss of grass and damage to his garden hy mud taken out of the new diversion of Dudley Crock. I have examined tbo drain, and find it reasonable. as he made this a condition of his agreeing to the diversion mare through his land. C. Napier Bell, Engineer. Tho Board sanctioned tho clearing of the river as far as the Christchurch quay. The Engineer was authorised to let the work referred to in the second paragraph of his report. The payment of Mr Baker’s claim for *5 was approved of. Mr Boss called attention to a report which had reached him him to the effect that tho mouth of the river Avon is so silted np that there is only one small opening for boats. Possibly wore this cleared the river would bo much improved. The Engineer said he would inspect the month of the river and see what conld be done. HEATH COTE ROAD BOARD. Letters from tho Heathcoto ko.d Board wore read, one calling attention to the oangeroua stats of the drain ou the we t side of the >tanmore road. from Worcester street to tho river, and requesting that it might bo piped, as the Board wished to make a footpath but cannot on account of the drain. This was referred to the engineer to report upon. The other letter called attention to the state of the Heathcoto river below Wilson’s hri’ge. It is almost choked with wat rcress. Tho letter also called attention to the way in which the clearing is being done above the bridge. This was referred to tho engineer. CALEDONIAN ROAD. A letter from E. Lindsay, of nlodonianroad, called attention to the state of the drain in the accommodation road opposite tho church on the Caledonian road. The drain is nearlv choked up and a few hours rain would flood Mr Lmd.-ay’s ground. It was resolved to expedite tho deepening of St Alban’s Creek, a ■ this deepening would re lieve the drain referred to. and many others which are similarly circumstanced. kbuse’s drain. The Chairman read a letter from Mr Horner, giving particulars of his claim for <£3oo compensation. There were price of < acres of land taken by the Board, .£195 and dam go to his private road, .£lO5. He objected altogether to the drain coming through his land. E.S. 1131. Mr Wright said tho matter had been one in dispute for many years. Ho would move — “That the Board decline to recognise Mr Horner’s claim.” Mr Hobbs seconded the motion, which was agreed to, CORRESPONDENCE WITH MB CLARE. C.E. The Chairman read a letter which he had written to Mr Clark and the reply thereto. Both letters have been already published. They referred to tbo objections which had been taken to Mr Clark s scheme for depositing excreta on the sandhills. ACCOUNTS. Accounts to the amount of about .£l6O were passed for payment. MR CARRUTHERS’ LETTER, At this stage of the proceedings the following letter was received by the chairman Christchurch, April 26th, 1878. To the Chairman of the Christchurch District Drainage Board. Sir,—l deem it due both to inysolf and to tho Board to make fome remarks on the plan of sewers prepared hy Mr Clark, showing wherein it differs from that I had the honor to prepare, and to state the reason which led me to adopt the latter rather than one similar in principle to that adopted by Mr Clark. The maiudifference in the two schemes is, that Mr Clark proposes to exclude the rain water from the sewers. and to pump everything which is allowed to enter them, that is, the sewage and subsoil water on to the Sandhills. I propose to admit the rainfall, and to allow the whole contents of the sewers, including the sewage, to flow to the Estuary, lor some years. In the future, when the population of the town shall have become so large that a perceptible nuisance would arise from doing so, I propose also to pump the sewage (except during storms of rain) to the Sandhills. I will first examine the matter from a financial point of vie w. As I stated in a former report, the cost of arranging the sewers iso that they conld carry rainfall as well as sewage, would be very little if at all greater than if thi-y were intended to carry sewage alone. The correctness of this view is amply borne out by Mr Clark’s plan and estimates. A comparison can in this case he easily made, as Mr Clark has adopted the arrangement of sewers which I had proposed. Of a total length of 57 miles of sewers, 45 miles consist of 9in. pipes. I had provided lOin. pipes, which are amply large to carry all tho rainfall. The difference in cost between 9in. and 10m. pipes is very small, as the excavating, laying, pumping and timbering for trenches, would be tho same for both ; the ouly difference would he the actual cost of the pipes, which is scarcely worth considering. The difference in the carrying capacity of the two sizes of pipe is as K'O to 133. The following table shows side hy side the whole of the built s«wers proposed in Mr Clark’s, and in the gravitation schemes, exclusive in both cases of the outfall sewers. It will he seen that Mr Clark very properly uses egg-shaped sewers, while in the gravitation scheme circular ones are preferred, as being under the different circumstances, more suitable than the other . LIST OF SEWERS.

The total length of built sewers is greater by 23$ chains in the gravitation than in Mr Clark’s system. This is flue to my having adopted one of the smallest size in Colombo road, where Mr Clark uses an 18inch pipe, and is really the only saving which has been made ; it does not, however, amount to mi re than £2 0, On the other band, Mr Clark is obliged to lay 60 chains of new 18-inch pipe in the South belt at a cost of £3600, ns the existing sewer is required to carry rainfall alone. The cost of the circular sewers would bo about the same (rather less than more) as that of the corresponding egg-shaped ones which replace them in Mr Clark’s scheme; the carrying capacity is, however, twice as great, so that without increasing the cost one penny, but simply from being able to adopt a better form, the gravitation system of sewers have the capacity required to carry the rainfall as well as the sewage. To show that nothing is saved by excluding the rainfall, I give the estimates of the two schemes side by side. ' ' Mr GravitaC 1 ark’s tlon Scheme. Scheme. ’ £ £ Sewers, Ac., exclusive of outfall sewer 120,640 123,856 Storm overflows at Waltham, &c., Ac 19,128 Total cost to beginning of outfall 139,768 12u,850 Outfall sewer j 13,365 59,730 ! 153,133 183,586 Contingencies at lo per coni. ... j .15,313 15,350 - ■■ ; —~— 168,416 201,015 Laud pumps, Ac., including 10, per cent, contingencies ... j 21,450 | 189,890 201,945 In my original estimate I put f he contingencies at 15 per cent. ; but as Mr Clark has only taken 10 per cent. I adopt this for the sake of comparison only. Tho financial position is as followslf the gravitation scheme be adopted t here will be an Immediate expenditure of £12,000 more than by adopting Mr Clark’s ; and at some future timesay in twenty years—a further expenditure of £21,450 will be required for pumps and preparing land for irrigation; but as the rain fall i 1) provided for, no further expendi:u;y \rill over be required. _ ’ • •• •••• ’ ’• ' r ' in Mr ClarJ’j? estimate a sum of 1)19,128 is put down to laake temporary provision for storms, by deepening n,ud opening out Jackson's Creek, and by Wpfti. fU? wsj is caly ths> first oi a vety

large expenditure for similar purposes which will be required hi the future. For example, the existing

outfall drain is required to carry the storm water, and mud be re built ami maintained. The tiinner work will only last a few years longer, and the brick work is already in a partly ruinous state. It will probably entirely collapse when the new sewer, as designed by Mr Clark, renewing the old at a lower level, is being built beside it. The cost of outfall three miles in length will be very considerable and alone will be sufficient to raise the total cost of Mr Clark’s to at leait as high a figure as tlint of the gravitation scheme. The whole of the low-lying part of the town at the corner of the Sou'll and East belts is subject to flood. The Ferry road drain has been made to relieve it, which it does in a not very satisfactory manner. When this drain is closed Jackson’s Creek is to be deepened about sft. so as to carry off the storm water. Open drains through a town always necome a neisance, and experience shows that they have sooner or later to bo closed in » ith brick sewers. In this ease the gradient is so flat (1 in 1320) that the creek must at an early date become a mere stagnant ditch of fonl water, and the Board must be prepared to make a new sewer down the Ferry road largo enough to carry all storm water to the Horthcoto. The same remarks apply to the open drains along the Lincoln road, and other places. They will all have to be couverted into sowers, and the cost of doing so wi 1 be so innch in excess of the cost of the gravitation scheme. I do not think the advantages which Mr Clark proposes to gain by excluding the rainfall are equal to those whioh have to bo sacrificed for the purpose; and as a largo increase of the total cost would be incurred by adopting his system, I would urge on the Board to carefully consider the question before doing so.

The first objection to tho admission of rainfall which Mr Clark makes (clause 20 of his report, is that the size of the sewers must be increased. This ie true of tho carrying capacity of the sewers, but not necessarily of their cost. A circular sewer will ofirry twice as much water as an egg-shaped one of tho same cost. The total cost of Mr Clark’s system of sewers up to the beginning of the outfall sower is £130,753, while that of tho gravitation system is only £123,856, so that up to this point there is au nctnal economy iu making the sowers (large enough to carry tho rainfall, and thus save t ,o cost of separate works for the latter purpose. The outfall sewer would cost £59,730 if made large enough to carry rainfall. One of half that carrying capacity to carry sewage only would cost about £15,000. The total cost of a set of sewers to carry rainfall and sewage to the list nary is, therefore, about the same as one to carry sewage alone, with provision made for a small part only of the expenditure which will eventually bo necessary to provide for the storm water.

The second objection is that road grit, outers tho sewers along with the rainfall, and that road grit is the most, difficult of all the matters which do enter tho sewer to remove to the outfall by suspension. This would be a valid objection if tbe velocity attainable in the sewers were not sufficient to remove all deposit. I have, however, given great care and attention to this, and so arranged the system of severs that a continuous stra in of pure water from the Avon or some of the numerous unfailing streams which flow through or near the town could be turned throngh the whole length of every sew >r. Tho whole system of sewers is thns perfectly self-cleansing either during rain or drought, and no foul air will be generated in any of them. This facility of admitting an unlimited supply of pure water permits the use of circular servers throughout instead of the more costly egg-shaped ones, and thus provision for rainfall as well as for sewage can be made without increasing tile cost at all. Tho mniu outfall sewer would not at high water have sufficient hydraulic inclination to keep quite clean, but any deposit which fell would be cleared out at low water, and in any case tbe cost of hand clearing would not exceed £SO a year. Mr Clark says he estimates the power to flush sewers as of less importance than the means of preventing its necessity, but the exclusion of road glut does not do away with this necessity. At least one half of the sewers will never bo nearly full, the sewage will trickle along them iu a tuin shallow stream, depositing a slimy sludge along the floor and sides. Mr Clark provides flushing only for tne intercepting sewers, and not even for all of them. A good flush from rain or otherwise would clear away tnis sludge, and should certniuly be allowed to do so unless there is some very strong reason to tho contrary. Where there is no outfall except by pumping, as iu Mr Clark’s scheme, it becomes almost necessary to exclude rainfall, but where an outfall can bo provided it should certainly bo done. Tho other objection made I>3 r Mr Clark, that tho fanner is bound to receive the largest quantity of useless sewage precisely at the time when it is most difficult to dispose of it, docs not apply in this case. During floods the diluted sewage would be allowed to flow through the outfall sewer to the Estuary, and would not be pumped on to tho Sandhi,ls a*, all.

Tho whole of Mr Clark’s objections to admitting tho rainlall into tjio sewers thus falls to the ground. Ist—Excluding the rainfall does not lessen the cost, but on the other hand will very largely increase it.

2nd—Admitting the road grit will not cause deposit in the sewers. 3rd —The sewage farmer will not be flooded out in rainy weather, more if rainfall is admitted than if it is excluded.

The objections to Mr Clark’s scheme are, besides the largely increased ultimate cost, very weighty. In the first place a system of sewers, which docs not admit of cleansing by rain nor even by flushing, is inferior to one which does, in the main respect, of freedom from offensive gases. It is objectionable, where it can be avoided, to depend entirely ou pumping, and to be obliged to pump the sub-soil water at night when there is scarcely any sewage mixed with it. Tho main objection is, however, that it does nothing to relieve the low-lying parts of the town from floods. A large part of Christchurch has no natural drainage; it was originally a swamp, and is now flooded at every heavy rain. If rain were admitted into the sowers these low-lying parts would he relieved from this groat evil, and would heconid as dry and healthy as the rest of the district. If the rain is not allowed info the sewers the Board must make up its mind at no distant date to provide a duplicate set for this purpose alone. I have the honor to, sir, Your most obedient servant, John Carruthees. It was resolved to take into consideration Mr Clark’s report on the sewage question at the next ordinary meeting, when the letter from Mr Carruthers would receive attention.

DRAINAGE RATE. Mr Foss moved “ 'i hit a committee, consisting of Messrs Duncan and Hobbs, be appointed to calculate the rate necessary for each part of the district for past and current expenditure during the year 1878, and that the committee report to a special meeting of the Board, to be held on Thursday, May 2nd.” Mr Wright seconded the motion, which was adopted. LITHOGRAPHED PLANS CONNECTED WITH MR CLARK’S REPORT. It was resolved to send lithographed copies of Mr Clark’s plana to various public bodies, and to leave orae with the booksellers for sale, at half a crown. The Board then adjourned.

Streets. Mr. Clark’s Scheme, Gravitation Scheme. Length in Chains. Dimensions. Length in Chains. Dimensions. East Belt 25 3ft. 9in. x 2ft. 6in. 25 3ft. 4in. diameter. East Belt 49 4ft. 3in. x 2ft. lOin. 46 3ft. 6in. ,, Kilmore street ... 31 4ft. Gin. x 2ft. 8in. 31 3ft. Sin. Kilmore street ... 24 2ft. 6in. x 1ft. Sin. 24 2ft. Gin. „ Madras strees ... 31 3ft. Oin. x 2ft. Oin. 31 2ft. Gin. ,, North Belt 18-1 2ft. 3in. x 1ft. 6in. 18} 2ft. Oin. ,, North Belt 5i 2ft. Sin. x 1ft. Gin. Nil. South Belt 15 3ft. 3iu. x 2ft. Gin. 15 3ft, Oin, South Belt 16} 3ft. Oin. x 2ft. Oin. 16} 2ft. Gin. „ South Belt 12 2ft. 9in. x 1ft. lOin. 12 2ft. Oin. „ South Belt 12 2ft. Sin. x l£t. lOin. Nil. Colombo Hoad ... Nil. 41 2ft. Gin. x 1ft. 8in. Total Chains ... 239} Total Chains 263