The sewage, from the discharge of which this calculation was derived—and the dryness of the weather must not be lost sight of—may be fairly assumed as derived (in a dry season) almost entirely from artificial sources or house drainage, as there was no rain-fall, or but little. “Supposing, therefore,” the Report states, “the entire surface to be urban, we have 540 cubic feet as the mean daily discharge per acre. If, however, the average be taken of the first eight outlets, viz., from Essex-street to Grosvenor-wharf inclusive, which drain a surface wholly urban, the result is 1260 cubic feet per acre in the 24 hours. This excess may be attributed to the number of manufactories, and the densely-populated nature of the locality drained; but, as indicative of the general amount of sewage due to ordinary urban districts, the former ought perhaps to be considered the fairer average.”
It is then assumed—I may say officially—that the average discharge of the urban and suburban sewage from the several districts included within an area of 58 square miles, is equal to 256 cubic feet per acre.
| Sq. Miles. | |
| The extent of the jurisdiction included within this area is, on the north side of the Thames | 43 |
| And on the Surrey and Kent side | 15 |
| Cubic Feet. | |
| The ordinary daily amount of sewage discharged into the river on the north side is, therefore | 7,045,120 |
| And on the south side | 2,457,600 |
| Making a total of | 9,502,720 |
Or a quantity equivalent to a surface of more than 36 acres in extent, and 6 feet in depth.
This mass of sewage, it must be borne in mind, is but the daily product of the sewage of the more populous part of the districts included within the jurisdiction of the two commissions of sewers.
The foregoing observations, calculations, and deductions have supplied the basis of many scientific and commercial speculations, but it must be remembered that they were taken between seven and eight years ago. The observations were made, moreover, during fine summer weather, generally, while the greatest discharge is during rainy weather. There has been, also, an increase of sewers in the metropolis, because an increase of streets and inhabited houses. The approximate proportion of the increase of sewers (and there is no precise account of it) is pretty nearly that of the streets, lineally. Another matter has too, of late years, added to the amount of sewage—the abolition of cesspoolage in a considerable degree, owing to the late Building and Sanitary Acts, so that fæcal and culinary matters, which were drained into the cesspool (to be removed by the nightmen), are now drained into the sewer. Altogether, I am assured, on good authority, the daily discharge of the sewers extending over 58 square miles of the metropolis may be now put at 10,000,000 cubic feet, instead of rather more than nine and a half millions. And this gives, as
| Cubic Feet. | |
| The annual amount of discharge from the sewers | 3,650,000,000 |
| The total amount of wet house-refuse, according to the calculation before given, is | 3,820,000,000 |
| Hence there remains | 170,000,000 |
| Sq. Miles. | |
| Now it will be seen that the total area from which this amount of sewage is said to be drained is | 58 |
| But the area of London, according to the Registrar-General’s limits, is | 115 |
So that the 3,650,000,000 cubic feet of sewage annually removed from 58 square miles of the metropolis refer to only one-half of the entire area of the true metropolis; but it refers, at the same time, to that part of London which is the most crowded with houses, and since, in the suburbs, the buildings average about 2 to the acre, and, in the densest parts of London, about 30, it is but fair to assume that the refuse would be, at least, in the same proportion, and this is very nearly the fact; for if we suppose the 58 miles of the suburban districts to yield twenty times less sewage than the 58 miles of the urban districts, we shall have 182,500,000 cubic feet to add to the 3,650,000,000 cubic feet before given, or 3,832,500,000 for the sewage of the entire metropolis.
It does not appear that the sewage has ever been weighed so as to give any definite result, but calculating from the weight of water (a gallon, or 10 lbs. of water, comprising 277·274 cubic inches, and 1 ton of liquid comprising 36 cubic feet) the total, from the returns of the investigation in 1844, would be