MR GORDON’S REPORT ON THE CITY WATER SUPPLY AND DRAINAGE.

Evening Star, Issue 4181, 21 July 1876, Page 4

MR GORDON’S REPORT ON THE CITY WATER SUPPLY AND DRAINAGE.

{Concluded.)

lI,—DRAINAGE. 1. There are three ways in which the sewage of Dunedin could be disposed of, viz.:— Ist, By drains entering the harbor; 2nd, By a system of drains connected with a main drain leading to the Ocean Beach ; 3rd, The dry system— i.e-, the removal by carts of all household refuse and the scavengings of the streets, the storm water only being allowed to enter the harbor. 2. Of these three, the first is, in my opinion, the worst, and should not be entertained even as a temporary measure. Ido not think there is any analogy between the Thames, where it receives the London sewage, and Dunedin Harbor. The latter more resembles the river at Westminster, and the tide would carry the contents of the sewers up and down; as it did at Westminster before the sewers there were intercepted. The nuisance was found to be intolerable. Another analogous case can be found at Sydney, where the sewage is discharged into the harbor, and there, too, it is found to be so intolerable that a complete change of the system, requiring a very great outlay, is in contemplation. At Dunedin it would be worse, as Sydney Harbor is deep all over, while at .Dunedin the filth would be deposited on the mud banks, and exposed to the air and sun for a considerable time each tide. I find from the report that in 1864 Mr Balfour was opposed to the conversion of the harbor into a , cesspool, as was also Mr Swyer. So was Mr J. Millar. Mr Hockeu, the city coroner, considered that it would be “ extremely unsafe.” I cannot find that any evidence, either engineering or medical, was at that time given in favor of making the harbor the receptacle of the sewage of the town, nor was such to be expected. In opposition to the professional advice given them, the Commissioners cite the Thames as an example in favor of their proposal that the sewage out-' fall should be into the harbor, forgetting, apparently, that the Outfall on the Thames was ex; rcssly located at a point where the sewage discharge.d on the ebb could- not be brought back by the flood tide. I need not say that the objection to this plan is constantly increasing. In 1872, however, Mr Mirams recommends the harbor as a natural and convenient outlet for the sewage. The medical officer, Mr Cole, strongly objects to the plan in his report of January, 1875, and I can only imagine it was recommended as the cheapest and. readiest way of doing something for the sewerage of the town.

3. I Jiave no hesitation in saying that if this plan of disposing of the sewage is adopted even as a temporary measure, the harbor will be polluted beyond the hope of e/er being purified again, and will resemble the waters of Venice, Amsterdam, and other places where the sewage is not removed. There is the additional objection that the sewers themselves would be stagnant during part of every t de. 4. The objections, of the Commissioners to the second method, which, would require the outlet to be at the Ocean Beach, are the costliness of the iVork and the pollution of a much-frequented promenade. JSTo doubt the works will be expensive, as all works for draining a large city, built like the proposed extensions Of Dunedin, little above higbmust be, but there need be no expensive works in connection with the shifting sands, nor need the sea be polluted in the smallest perceptible degree. There is abundance of space for constructing filtering beds through which the sewage can be filtered, so as to enter the sea in a practically pure state,. It Would; have to be lifted to about ten feet above high water at the sea. o. The third or “dry” system is an expensive one, but it is, when it and street scavenging are carefully performed, a very efficient oiie, and in thinly-populated streets it is probably less expensive than sewerage. One of the “dry” systems, Liernurs, has much ..to recommend it in crowded cities where no natural fall, for sew-rs could be obtained. It consists in the removal in cast iron pipes, by pneumatic force, of all the fdscal matters, kitchen refuse, and the mud of the streets, which is always mixed with fcecal matter, all of which must be excluded from the . sewers. But sewers are still rc-

quired for' removing the ordinary house drainage from wash-houses, baths, &c. His system is only ah improved means of removal, and this could be done sooner in a scattered town more economically by carts. 6. In the following recommendations I must, of course, confine myself to general principles, leaving the details to be worked out when the proper preliminary work has been done, notably that recommended by Mr Swyer ten years ago. These details must be prepared with reference to the population and localities to beeventually supplied with water, and it is evident that any comprehensive system of-sewerage should include all the suburbs that lie within the watershed, or can be served by the main drain leading to the beach.

My recommendations are: (a.) The immediate compulsory abolition of all cesspits, whether open or closed ; the removal of their contents, and the substitution of the dry earth system for them, and also, until the sewers are finished, for waterclosets. Zymotic disease has decreased or disappeared in Melbourne exactly as the cesspool system'has • been abolished, and frequent removal adopted,' *. (M The systematic periodical removal of all household -refuse, : as well as the contents of the earth-closets, by meii employed by < the body charged with the sanitary care of the.City, There should be very strict . regulations and penalties for any breach of them.

... (c.) A thorough system of street scavenging and removal of the refuse, and the removal of all depfits of filth to a distance, without which cleanliness within the premises would only effect half the- improvement needed. The above seem to me to be required for the immediate abatement of the present unsatisfactory state of things. The following are for the permanent sewerage, (d.) A main sewer along the present front of the town, receiving on one side the clrain- . age of the present town) and on the other that of ttie' proposed reclamation, and conveyingit to the nearest point of the Ocean Beach by the shortest route, there to be pumped up to a sufficient height, and filtered through six feet of sand and discharged above high-water level by drain-pipes. This main sewer should be capable of discharging 100 gallbns per head per day, and should be furnished Atiih gates for flushing when opportunity offered it should deliver into a well, of which the surface could be lowered by pumping to several feet’below the floor of the sewer at its.lower .end, to facilitate Hush- J ihg. The best fail for the sewer would he /abdot- feur feet per .mile, but it could'be I made r -less if, it was found very expensive to secure - that fall. Cleansing by , natural labor would then have to be provided-for. The pumping should be nearly continuous, and the machinery required would probably ' r .be a double set of pumps and engines, of forty horse power each, one to be in reserve.

■ - {?.) A system of drains, afj first in all the most populous, streets only, but of such a capacity as will accomodate the drainage of other districts beyond them, as they may re- _ '.qmre it, reckoned at 100 gallons per head ■pertlay.' f - - ■;'(/•••) The .exclusion of the extreme flood • infant ijcqupi tbs sowers,. They could be dis-

charged into the harbor without any bad effects, as they would be ■ but slightly impregnated • with vocal matter, and their a gg le ß a te annual volume would be compara-. tively small, while all the heavier matters brought down could be received into wells before entering the harbor. The interception of the-, ordinary street drainage, and the passing of the Hood water, could be managed by inexpensive arrangements.

’{(/■) -No factories should be allowed to discharge impure water into the harbor. It should be purified first, or discharged into the sewer. As to the modes of purification, I beg a reference to the Reports of the Royal Commissioners on the Pollution of Rivers.

7. I can hold out no hope of any system of sewerage being remunerative, as Mr Swyer and Mr Millar imagined it would be ; but some revenue might be got from the filtering areas, which would produce heavy crops. This has been proved at Merthyr Tydvil. An excellent kind of potato is grown in Holland on blown sea sand well manured.

8. It must be confessed that the best mode of sewage removal is a. matter in which engineers at Home differ very much. Sevoial totally different systems are each supported by eminent men, while probably more will agree that the problem has not yet been solved. There are always, however, some methods which are inapplicable to particular cases, and in the case of Dunedin meadow irrigation and sewage farming by gravitation are impossible, and the main sewer will be needed whether the filtration or the dcssiccating and deoclerising or any other system be adopted, except that very generally in use m the north of England, viz., the dry system, or the probably cheaper, but most antiquated, and, in my opinion, the worst possible of all plans, viz., that of discharging all the filth into the water immediately in front of the town.

9. .No estimate of the cost of sewering Dunedin can be framed from that of towns in England without corrections, for (1) more abundant use of water ; (2) greater length of sewer per head of population ; and (3) greater cost of labor and materials. The cost of the removal of house refuse on the dry system in Melbourne is, I am informed, Is 5d to 2s lOd suburbs, and 4s 5d in the City, The cost of sufficient scavenging! cannot give, as it cannot be said to be practised .there any more than in Dunedin, as far as my observation goes. In conclusion, I have to acknowledge the courtesy of yourself, and Messrs M'Kerrow, Mi rams, and M‘Gregor, in furnishing me with information, and to state that if any part of the above report is not quite clear to you, I shall be glad to give any explanation you may desire.—l have, &c., G. Gordon, M. Inst., C.E. J. M. Massey, Esq., Town Clerk, Dunedin, N.Z.

Melbourne, 7th June, 1876. Sir, —Your telegram received yesterday informs me is desired to deliver water at 800 ft above sea level, and consequently far above the limit c nmuauded by the present work, but it does not inform me of the number of inhabitants to be provided for within and beyond these limits respectively. The map would seem to show that there are very few houses so high as 800 ft above the ■pit. It would be well if you could specify the number likely to be supplied from, say, 300 to 600, and from 600 to 800 ft above sea level. It becomes a question whether it would be desirable to construct gravitation woi ks at so high a level for a very limited number of persons. - I have, &c., . .. 1r G. Gordon, J. M. Massey, Esq., Town Clerk, Dunedin. Melbourne, 9th June, 1876. Sir,—With reference to paragraph nine of my report, Part 11. ■ The cost of emptying closet pans and pits is from 2s lOd in some of the .niburbs to os, and 6s in others and in the City, per head of the population. The cost of scavenging (imperfect) and removal of house refuse and other than closet pans is from Is 5d to 2s lOd in the suburbs, and 4s 5d in the City, per head of the population.—l have, &c., T G. Gordon, J, M. Massey, Esq., Town Clerk, Dunedin.

Melbourne, June 13, 1873. I have the honor to acknowledge the receipt of your letter of the sth instant, “explanatory of a misconception” on ray part of your answers to my queries respecting the requirements of Dunedin. You will allow me to point out that the meaning I attached to your replies was the only one they could bear My first query was The number of inhabitants for which it is desirable to provide a prospective supply within the limits which would be commanded by the

present works, or say 250 ft above sea level to which you replied—-“ 100,000 people,” My second query was—“ The same beyond such limit, and the highest point to be reached by the mains ?” and to this you replied—“No further number—only to provide for 100,000 inhabitants in all.” The only inference I could draw' from the above was that you contemplated a prospective increase in the population to be supplied below the limits of level of the present works up to 100,000, and that you did not contemplate supplying the high-lying suburbs. If you will be so good as to inform me by telegraph whether it will meet your views if I assume 75,000 as the population under the aforesaid limit, and 25,000 above it, I will send you a supplementary report as soon as possible.—l have, &c., G. Gordon, J. M. Massey, Esq., Town Clerk, Dunedin.

Melbourne, July 4, 1876. Sir, —Having been apprised by your telegrams of sth June, 1876 ; 7th June, 1876, and 27th June, 1876, and your letter of the oth of June, that the replies contained in your communication of the 18th of April to the first two of my queries, dated 16th of March, did not actually state the requirements of the City Council as regards the future water supply of Dunedin, and that a district higher than the present works would have to be supplied, I have the honor to send, as requested, the following remarks, as a supplement to my report, dated the 26th of May : -

2. It is stated in your last telegram that the numbers of people to be ultimately provided for may lie taken at 75,000 below and 25,000 above the present limits of supply, ihe daily supplies to those in summer will therefore be—at the rate of 60 gallons per head—4\ and 1V million gallons respetively ; [.the total quantity and the necessary storage remaining the same as before, and only°a diflerent mode of distribution from the storage reservoirs on the ‘Water of Leith (paragraph 6 of report) being necessary. 3. To supply the upper district from this source with sixty gallons per head per day would require probably six miles of 15-iuch main and a service reservoir, costing probably L 27,500. Add about fifteen miles of reticulation pipes, say Llß,ooo—-together, L 45.500; to which would have to be added, as the cost of supplying the upper district, one-fourth of the cost of diverting the streams ami constructing the reservoirs mentioned in paragraphs 6 and 7 of my first report.

4. If for the present the Town Council mfine themselves to the supply suggested

in paragraph 9 of my report, then, taking the population below the present limits at 35,000, and that above at 10,000 —nearly the same proportion as that given above—a 12-inch pipe would be required for the upper district, and a small pipehead reservoir near the supposed site of Mr Barr’s proposed lower dam, where the level of the stream could be raised 860 ft above the sea. These would cost probably L 18,500, and the service reservoir, and half the reticulation mentioned above, L 12,500 ; in all, probably L 31,00 heavy outlay for the preset population, but by no means excessive for 10,000 persons. In England, a cost of L2 per head for little more than half the quantity of water is a fair rate of cost. To increase the supply afterwards, if required, up to that of 25,000 persons, would cost probably L 17,750 in addition.

5. Although Ido not consider it absolutely necessary at present, it would be prudent to increase the present storage capacity. Two sites offer themselves—viz., one on the stream above the present reservoir, which would be commanded by the race from Nos. 1 and 2 streams, and which, as regards cost, would probably be more favorable than the other which is on the Water of Leffh, but it would be more dangerous, and therefore, I think, inferior. The second would have greater security, and the additional advantage of commanding the high-level district, and the dam might be so constructed as to form part of the work eventually to be needed when the population increases, as contemplated, to 100,000, 6. The allowance of 60 gallons per head in summer, and 40 in winter, may by some be considered excessive, but it is only by stringent regulations, and the greatest care and watchfulness, that the Melbourne supply has been brought down to a little below that rate. Sixty gallons is nearly double what is allowed in England, but a more liberal use of water is already an established habit here, and the consumption per head is yearly increasing in England. In Dunedin it will require constant care, vigilance, and firmness to keep the consumption down to that rate, as people are already, it would appear, in the habit of using water lavishly. However desirable an “ unlimited” supply of water may be, it is an expensive luxury, and in many cases, of which I think Dunedin is one, it cannot be obtained from any suitable source in the neighborhood.—l have, &c., G. Gordon.