CITY DRAINAGE AND SEWERAGE.

Evening Star, Issue 3057, 5 December 1872, Page 2

CITY DRAINAGE AND SEWERAGE.

The City Surveyor, af last nighji’s meeting of the Ui;y Council, presented a long and exhaustive report on diraipage £(, nd sgwerage. In bis introductory remarks he alludes to the facilities for thorough drainage through one-third of the city being built on hill-sidea, and to the improvements occasioned by the low flat over which storm water has to pass, aud the inconsiderable rise and fall ot the tide. This is not in every case sufficient to allow of storm water running off the streets, nor to drain cellars. Oomple.e drainage should provide for the collection and underground disposal of(1.) Sewage from buildings ap 1 building areas. (2.) Water from streams or springs flowing iuto or existing m the city. (3.) Storm water brought into and flowing through the city from surround* mg districts. (4.) Bain-water falling upon the city area, (fl.) For the collection of the sewage iuto settling tanks; the separation of the solid from the liquid sewage; its deodorizatiou and distribution for agricultural purposes. The last point the Surveyor does not propose to discuss, as “the harbor presents a natural and convenient outlet for all sewage matter, without detriment to anything or anybody, and the value of any manure which, after an expensive process of collecting, preparing, aud distributing, could be obtained, is nob worth consideration under present circumstances.” By a new system adopted at Bishop 6fcorlford, containing 6000 inhabitants, two tops weekly were obtained, at whichrate Dunedin, with 18,000, would give but six tons. This is not worth consideration when running into a large harbor like ours. Dunedin can be drained iuto the sea at once if the outlets are placed at such a level that during 12 out of 24 hours they will be partially or wholly covered with water. The Surveyor explains that by his plan ihere will be no risk of polluting the Water of l eitb, as he proposes to intercept “ all the waters ” at convenient points and convey them into the Bay. Mr Mirama then refers to the report of the Sanitary Cownxis*

sion appointed in 1865, and comments on the various schemes proposed Adopting the conclusions of the i ommissioners, he remarks that the problem to be solved is expressed in the first four divisions, but as he proposes “to carry below the surface the ■whole of the storm water falling upon the city,” the 3rd and 4th divisions require mainly to be considered. He estimates that it is necessary to get rid of half a cubic foot per hour fur each inhabitant, and he calculates the greatest discharge at 25,000 cubic feet per hour, which he purposes to get rid of by an oviform sewer, 3 feet by 2, with a fall of 1-1000 at 13 feet below the surface. He proposes special provisions for low-lying lands. For subsoil drainage, bo suggests two-inch pipes along each side of the sewers, running into the ground horizontally, with here and there some of the arch-joints dry. Mr Mirams then examines various propositions and considers their adaptability, and in voluminous details gives the dimensions of the sewers for each street. Tho levels given for the outfall sewers are No. 1, High street. 1 inch in 729 ; No. 2, Mnn-'r place, 1 inch in 330; No. kt Ardiew street, 1 inch in 812; No. 4, Frederick street, 1 inch in 445 ; No. 5, bit. Daviu street, 1 inch in 267. The depths of the crowns of tho sewers below the smfacc would vary from 2 feet 10 inches to o feet; and of the invert, from 5 feet 6 inches to 9 feet 6 inches. The brick lining of the sewers to be only 4-i inches in thickness. The branch sewers to be 2 feet 6 inches by 1 foot 10 inches. The total cost he estimates at L 104,582.