Of the Quantity of Metropolitan Sewage.
Having estimated the gross quantity of wet house-refuse produced throughout London in the course of the year, and explained the two modes of removing it from the immediate vicinity of the house, I will now proceed to set forth the quantity of wet house-refuse matter which it has been ascertained is removed with the contents of London sewers.
An experiment was made on the average discharge of sewage from the outlets of Church-lane and Smith-street, Chelsea, Ranelagh, King’s Scholar’s-pond, Grosvenor-wharf, Horseferry-road, Wood-street, King-street, Northumberland-street, Durham-yard, Norfolk-street, and Essex-street (the four last-mentioned places running from the Strand). The experiments were made “under ordinary and extraordinary circumstances,” in the months of May, June, and July, 1844, but the system is still the same, so that the result in the investigation as to the sewage of the year 1844 may be taken as a near criterion of the present, as regards the localities specified and the general quantity.
The surface drained into the outlets before enumerated covers, in its total area, about 7000 acres, of which nearly 3500 may be classed as urban. The observations, moreover, were made generally during fine weather.
I cannot do better by way of showing the reader the minuteness with which these observations were made, than by quoting the two following results, being those of the fullest and smallest discharges of twelve issues into the river. I must premise that these experiments were made on seven occasions, from May 4 to July 12 inclusive, and made at different times, but generally about eight hours after high water. In the Northumberland-street sewer, from which was the largest issue, the width of the sewer at the outlet was five feet. In the King-street sewer (the smallest discharge, as given in the second table) the width of the sewer was four feet. The width, however, does not affect the question, as there was a greater issue from the Norfolk-street sewer of two feet, than from the King-street sewer of four feet in width.
| Northumberland Street. | ||
| Date. | Velocity per second. | Quantity discharged per second. |
|---|---|---|
| Feet. | Cubic Feet. | |
| May 4 | 4·600 | 10·511000 |
| „ 9 | 4·000 | 6·800000 |
| June 5 | 4·000 | 6·800000 |
| „ 10 | 4·600 | 10·350000 |
| „ 11 | 4·920 | 12·300000 |
| „ 16 | 3·600 | 5·940000 |
| July 12 | 2·760 | 3·394800 |
| 56·095800 | ||
| Being Mean Discharge per second | 8·013685 | |
| Ditto per 24 hours | 692382· | |
| King Street. | ||
| May 4 | ·147 | ·021756 |
| „ 9 | ·333 | ·079920 |
| June 5 | ·170 | ·020400 |
| „ 10 | ·311 | ·064688 |
| „ 11 | ·300 | ·048000 |
| „ 16 | ·101 | ·004040 |
| July 12 | ·103 | ·008240 |
| ·247044 | ||
| Mean Discharge per second | ·035292 | |
| Ditto per 24 hours | 3049· | |
Here we find that the mean discharge per second was, from the Northumberland-street sewer, 692,382· cubic feet per 24 hours, and from the King-street sewer, 3049 cubic feet per 24 hours.
The discharge from the principal outlets in the Westminster district “being the mean of seven observations taken during the summer,” was 1,798,094 cubic feet in 24 hours; the number of acres drained was 7006. The mean discharge per acre, in the course of 24 hours, was found to be about 256 cubic feet, comprising the urban and suburban parts.
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
| Tons. | |
| Quantity of sewage daily emptied into the Thames | 278,000 |
| Ditto Annually | 101,390,000 |
In September, 1849, Mr. Banfield, at one time a Commissioner of Sewers, put the yearly quantity of sewage discharged into the Thames at 45,000,000 tons; but this is widely at variance with the returns as to quantity.