The Sewerage of Melbourne.
Health is wealth is an axiom, but wealth does not always mean health. The Melbourne Board of Works has failed to appreciate the difference. Having recognized the necessity of an extensive sewerage scheme to improve the health of the city, and having wisely called for the advice of Mr. Mansergh, they now propose to amend that able engineer’s scheme-to minimize by a small ratio the cost of the works, and that at the expense of injuriously affecting the efficacy of the scheme. Mr. Mansergh, it may be remembered, proposed the water carriage system. That was agreed to, as also the suggestion that the sewers should be designed for the maximum water supply of seventy-five gallons per head, the population being based upon the forecast fifty years hence 1, •’00,000, and the half of the sewage was to be delivered in six hours. It is in the most essential details that the changes have been made. Mr. Mansergh took as his dividing line a stretch of elevated ground running nearly north and south through the centre of the metropolitan area. All the sewage west of that line was to gravitate to one pumping station, and from thence was to be distributed over a sewage farm, while everything east of the line was to go in another direction and be similarly treated. The size of the main sewers were to vary from eight feet, six inches to fourteen feet, and their normal flow was to be half full, whilst at the same time they were to have self-cleansing velocities when passing only the quantity due to the population using them in the first year of their construction. Under these conditions it is manifest that in respect of efficient flow and self cleansing ability, these sewers would go on improving year by year as the volume of sewage passed into them increased with the gradual growth of population. He further designed that the pipes should be sufficient to carry away all sewage excepting the rain water from the front roofs or front gardens. Nothing that could carry with it even a suspicion of pollution was to be allowed to find its way into the gutters and thence into the river. According to the amendation only the rainfall from “exceptionally polluted surfaces” will be passed into the sewers. This decision is to be regretted for many reasons, and notably for its indefiniteness. The pertinent questions are asked : “ Shall the back yard sink drain into the sewer or into the gutter ? “ “Shall the water from the back roofs be kept separate from the back yard sink ? ” If so, who shall insure that offensive sewage will not be passed to the gutter pipes? Many other similar difficulties are involved. Again it is proposed that the sewers leading to the pumping stations be designed to carry the quantities specified when running twothirds full instead of one-half, as proposed by Mr. Mansergh. This latter change has been made principally at the suggestion of Mr. Thwaites, who contends that the reduction of the size of the pipe will minimize the possibility of sewer gas collecting and escaping, but it is a moot point. Besides, whereas in Mr. Mansergh’s scheme there is a likelihood of the sewage overflowing into the street two days in the year by reason of rain, it may in the other case overflow eighty days’ engineering.