214 



Art. LTI. — On Sewage Irrigation, and its results, with a Sketch of the 

 Main Drainage Systems of London and Paris. By T. S. Tancred, 

 Assoc. Inst. C.E. 



[Read before the Philosophical Institute of Canterbury, August 4, 1869.] 



There are few subjects more interesting to the inhabitants of towns generally, 

 than questions relating to sanitary arrangements, and properly organized 

 systems of main drainage. 



Although it might be thought that in every large town, such a system had 

 been in partial operation since the tunes of the Cloaca Maxima, yet it is a curious 

 fact that, until very recently, no large city, either in England or on the 

 Continent, had paid any real attention to this important subject. 



The author therefore proposes to state, briefly, what steps have been taken 

 in London and Paris to secure effectual drainage, and to compare the working 

 of two distinct systems varying in some important particulars. 



Up to the year 1815 it was illegal to discharge any sewerage into the 

 drains of the city of London. After that date it became impossible to prevent 

 the influx of sewage matter, and in 1847 the law was reversed, and drainage 

 into sewers rendered compulsory. 



Commissioners were appointed to carry out the various works necessitated 

 by such a change, and held office until the year 1856, when the present 

 Board of Works was constituted. 



The Board, after full investigation, resolved to adopt the scheme 

 elaborated by their own engineer, Mr. Bazalgette, under whose most able 

 administration the works were commenced in the year 1859, and will probably 

 be completed in the course of a year or so, contemporaneously with the 

 Thames embankment. 



In Paris the cholera attack of 1832 first opened the eyes of the inhabi- 

 tants to the sanitary condition of the city, and such vigorous measures were 

 adopted, that in four years their sewerage system was doubled, and within the 

 next twenty-two years quadrupled. Paris is built in blocks, each block having 

 its own cesspool, which is emptied at stated times, the contents deodorized and 

 part sold. All waste water from the houses, and rainfall, passes into the 

 sewers, which are of sufficient diameter to allow of men working freely in their 

 interior, and of their serving as subways for the conveyance of gas and water- 

 pipes, and lines of telegraph. They are cleaned by means of trucks running 

 on iron rails, and in the case of the main sewers, by a species of boat propelled 

 by the pressure of the water. The annual cost of cleansing amounts to about 

 ■£30,000, whilst it is understood that little or nothing is realized by the sale of 

 deodorized soil. 



Many difficulties arose in dealing with the sewage of London, as is 

 generally the case in every town which has been built before any definite idea 

 has been formed as to the ultimate disposal of its sewage ; one of the main 

 difficulties being, that the discharge was affected by the tide, a considerable 

 area being below the level of high-water. 



The six questions which presented themselves were : — 



1. At what point, and at what state of the tide, could sewage be dis- 

 charged into the river, so that it should not return within the more densely 

 inhabited portions of the metropolis 1 



2. The minimum fall of the intercepting sewers ? 



3. The quantity of sewage to be intercepted, whether it passed off 

 uniformly day and night, or in what manner 1 



4. Was rainfall to be included, and what was its probable amount ? 



5. Having regard to all these points, how were the sizes of the sewers to 

 be determined ? 



