DRAINAGE OF THE CITY.

New Zealand Times, Volume XXXII, Issue 5214, 7 December 1877, Page 3

DRAINAGE OF THE CITY.

The following letter from Mr. C. Napier Bell, C.E., was laid on the table of the City Council yesterday Christchurch, 27th November, 1877. _ Si r> —l have read the reply of Mr. Climio to my report, in which he denies most of the statements I have made with regard to his plans, explains away others, and accuses me of ignorance, misrepresentation, prejudice, and want of knowledge of the subject on which I reported. The manner in which this reply, as well as Mr. CiinnVs letter of 22nd November, was received by some of your honorable City Council, would seem to put the Consulting Engineer in the very peculiar position of being on the defensive against a man advocating his own scheme, and trying to get the City Council to adopt it. I beg your Worship to remind the City Council that I am not competing with Mr. Climie in a scheme for drainage, as the City Council have not asked me to prepare a design for the drainage of Wellington; X have no other interest in the question than to sec that the city does_ not, with my consent, enter on the construction of what X consider to bo an extremely unsuitable scheme of drainage, and I should not have condemned Mr, Climie’s scheme unless I had known that a better method was available to attain the end in view. As adviser to the city on this subject, I disapproved of the article which was offered to it, and the usual course adopted in such cases would have been to request the competing designer to modify his design to the satisfaction of the Consulting Engineer, or else to ask another man to submit a new design. Under the circumstances the City Council has taken the best course, which was to, "et the opinion of Mr. Clark. That being done, I should have preferred that nothing more were said on this subject until that gentleman had given his opinion. Mr, Climie, however, seems to have convinced some of the City Council that ho had met all my objections, completely vindicated his scheme as set forth in Ills report of January 11, 1877, and convicted me of misrepresentation, ignorance,

prejudice, &c., and from remarks made at the meeting of the City Council, I inferred that the position in which X have been placed by it is not clearly understood by some of the members. This position, as X understood it, is that I am appointed to see that the city does not accept and pay for »u inferior article m the way of a drainage project, and generally to watch the design and its execution in and through all its details. , . X should be very sorry to offer trivial or captious objections to any man’s work with no other object than to thwart and annoy him; the objections I made to the scheme or Mr. CHmie aro of importance, and have not been met nor answered in his reply. 1, As to the feasibility of turning the sewage* into the bay in case of accidents to the pumps, I stated in my report that the sewage would rim into the bay after the mam sower had filled from the pumps to the nearest overflow. There is nothing in the plans or sections to show how this is to be avoided, nor can it bo, as all the sewers of the Te Aro part of the town drain towards the main sewer at Kent-terracd, and apparently overflow towards the main sewer next the shores of the bay, which is itself below H.W.M. Tliis is a faulty arrangement of the sewers, the reason for which would be evident to most engineers. I never, however, said in my report that, if the pump failed, the sewage would stagnate in the street sewers; this is impossible, as the streets are so steep and high ; but it would stagnate in the tunnel until the pumps could empty it. 2. A chain pump has no valves, but has buckets ; it is probably less liable to choke than other pumps, bat is liable to jam or have its backets stripped by objects getting into the case.

3. In heavy rainstorms the rainfall would exceed the pumping power, and while that happens the sewers would overflow with the pumps in full work, and would continue to do so until the rain abated to the power of the pump, after which the pump would keep down the overflow. 4. I acknowledge in my report that pumping niglit and day could be done, if necessary ; I should not care to advise it in the case of a town like Wellington. 5. Regarding the sizes of the street pipes, the plans of Mr. Ciimie do not include a diagram map showing drainage areas ; for that reason I stated that I did not understand how he had arrived at the proper sizes. Before I attempted to give an opinion I constructed one very carefully, from which I came to the conclusion that from £6OOO to £7OOO could have been saved in the sizes of the street pipes. The argument in Mr. Ciimie’s reply, that my objection to the sizes was groundless, because all the house drains added together made up 250 times the capacity of the outfall sewer, is unanswerable, and I would recommend him to point that out to Mr. Clark. 6. Influx of subsoil water into tunnel. The tunnel lies about 100 feet below the surface, and also below L.W.M. Under these circumstances, the only way I can see to keep the subsoil water out, would be to add greatly to the cost of the tunnel in construction, and with douful result. The following are my grounds for quoting the cases of English sewers:—-Bedford, pumping, total sewage in twenty-four hours, 700,000ga15., of which 300,000 was subsoil water ; Warwick, pumping, 700,000 gals.; subsoil water, 230,000ga15.; Worthing, pumping, 480,000 gals. ; subsoil water, 130,000 gals.; Kendall, gravity, 750,000 gals. ; subsoil water, 350,000ga15. ; Chorley, gravity, 500,000 gals.; subsoil water, 200,000 gals.; Coventry, 2,000,000ga!s.; subsoil water, 500,000ga1a..; Halifax, gravity, 2,500,000 ; subsoil 500,000 gals. On looking up my authority, I find 1 have overstated the proportions, which are still very considerable.—Report of a committee appointed by the President of the Local Government Board, to inquire into the several modes of treating town sewage, 1876, London. 7. My report did not find fault with the size of the tunnel, it merely mentioned that the outfall 3.0 sewer from the pumps to the sea gave ample room for a large increase, the tunnel is vastly in excess of the requirement, but I do not think it can be constructed much smaller. 8. “ The only serious objection I have raised” against this scheme is not the “ draining back of the sewage” in the tunnel. This is a very trifling matter, and all the other objections are also trifles compared to my main objection, which is that a city like Wellington, standing on high rising ground, shall be sewered and drained by pumping, “night and day,” all its sewage, rainfall and subsoil water, which is the project offered by Mr. Ciimie for the city’s acceptance, and rejected by me on its behalf. 9. As to estimated cost of the scheme, I have a large experience in estimating engineering works, but I will not be too positive on this subject, if the contract can be let to the substantial experienced contractors mentioned in the reply for the amount of Mr. Climie's estimate. I have given details of the cost of the tunnel from sketch plans made by myself for this purpose, as there is no drawing of the tunnel among these plans. Any estimate for the tunnel is more or less guess work until the shafts are sunk to the level of the tunnel, to test the nature of the rock, and the amount of water in it. 10. As to the finish of the plans, I must request your 'Worship to give them to Mr. Clark, just as they are, as it will be easily seen that if they are altered, amended, and thoroughly finished up after leaving my hands, there would be no evidence left of the facts upon which ray report was founded. To save myself against contradiction, I have shown these plans, and those for Christchurch, to two or three men capable of judging.—l have, &c. f C. Napier Bell. To his Worship the Mayor of Wellington,