Of the Kinds and Characteristics of Sewers.
The sewers of London may be arranged into two distinct groups—according to the side of the Thames on which they are situate.
Now the essential difference between these two classes of sewers lies in the elevation of the several localities whence the sewers carry the refuse to the Thames.
The chief differences in the circumstances of the people north and south of the river are shown in the annexed table from the Registrar-General’s returns:—
| London. | North side of the River. | South side of the River. | |
|---|---|---|---|
| Elevation of the ground, in feet, above Trinity high-water mark | 39 | 51 | 5 |
| Density, or number of persons to an acre, 1849 | 30 | 52 | 14 |
| Deaths from Cholera to 10,000 persons living, in 60 weeks, ending Nov. 24, 1849 | 66 | 44 | 127 |
| Deaths from all causes annually to 10,000 persons (5000 males, 5000 females) living, during the 7 years, 1838-44 | 252 | 251 | 257 |
Here, it will be seen, that while the houses on the north side of the river stand, on an average, 51 feet above the high-water mark of the Thames, those on the south side are only 5 feet above it. The effect of this is shown most particularly in the deaths from cholera in 1849, which were nearly three times as many on the south as on the north side of the Thames. It is said, officially, that “of the 15 square miles of the Urban district on the south side of the river Thames, three miles are from six to seven feet below high-water mark, so that the locality may be said to be drained only for four hours out of the twelve, and during these four hours very imperfectly.... When the tide rises above the orifices of the sewers, the whole drainage of the district is stopped until the tide recedes again, rendering the whole system of sewers in Kent and Surrey only an articulation of cesspools.”
That this is but the fact, the following table of the elevation in feet above the Trinity high-water mark, as regards the several districts on the Surrey side of the Thames, may be cited as evidence.
| Elevation. | |
|---|---|
| Lewisham | 28 |
| Wandsworth | 22 |
| Greenwich | 8 |
| Camberwell | 4 |
| Lambeth | 3 |
| St. Saviour (Southwark) | 2 |
| St. Olave | 2 |
| Bermondsey | 0 |
| Rotherhithe | 0 |
| St. George’s (Southwark) | 0 |
| Newington (below high water) | 2 |
From these returns, made by Capt. Dawson, R.E., the difficulty, to use no stronger word, attending the sewerage of the Surrey district is shown at once. There is no flow to be had, or—the word more generally used, no run for the sewage. In parts of the north of England it used to be a general, and still is a partial, saying among country-people who are figuratively describing what they account impossible. “Ay, when? When water runs up bank.” This is a homely expression of the difficulties attending the Surrey sewerage.
There is, as regards these Surrey, more than the Kent, sewers, another evil which promotes the “articulation of cesspools.” Some of these sewers have “dead-ends,” like places which in the streets (a parallel case enough) are known as “no thoroughfare,” and in these sewers it is seldom, in any state of the tide, that flushing can be resorted to; consequently these cesspool-like sewers remain uncleansed, or have to be cleansed by manual labour, the matter being drawn up into the street or road.
The refuse conduits of the metropolis are of two kinds:—
- 1. Sewers.
- 2. Drains.
These two classes of refuse-charts are often confounded, even in some official papers, the sewer being there designated the “main drain.” All sewerage is undoubtedly drainage, but there is a manifest distinction between a sewer and a drain.
The First-Class Sewers, which are generally termed “main sewers,” and run along the centres of the first-class streets (first-class alike from the extent or populousness of such streets), may be looked upon as underground rivers of refuse, to which the drains are tributary rivulets. No sewer exists unconnected with the drains from the streets and houses; but many house-drains are constructed apart from the sewers, communicating only with the cesspools. Even where houses are built in close contiguity to a public sewer, and built after the new mode without cesspools, there is always a drain to the sewer; no house so situated can get rid of its refuse except by means of a drain; unless, indeed, the house be not drained at all, and its filth be flung down a gullyhole, or got rid of in some other way.
These drains, all with a like determination, differ only in their forms. They are barrel-shaped, made of rounded bricks, or earthenware pipeage, and of an interior between a round and an oval, with a diameter of from 2 to 6 inches, although only a few private houses, comparatively, are so drained. The barrel drain of larger dimensions, is used in the newer public buildings and larger public mansions, when it represents a sort of house or interior sewer as well as a house main drain, for smaller drains find their issue into the barrel-drain. There is the barrel-drain in the new Houses of Parliament, and in large places which cover the site of, and are required for the purposes of several houses or offices. The tubular drain is simply piping, of which I have spoken fully in my account of the present compulsory mode of house drainage. The third drain, one more used to carry refuse to the cesspool than the sewer, but still carrying such refuse to the sewers, is the old-fashioned brick drain, generally 9 inches square.
I shall first deal with the sewerage, and then with the house and street drainage.
The sewer is a twofold receptacle of refuse; into it are conveyed the wet refuse not only of many of the houses, but of all the streets.
The slop or surface water of the streets is conveyed to the sewer by means of smaller sewers or street-drains running from the “kennel” or channel to the larger sewers.
In the streets, at such uncertain distances as the traffic and circumstances of the locality may require, are gully-holes. These are openings into the sewer, and were formerly called, as they were, simply gratings, a sort of iron trap-doors of grated bars, clumsily made, and placed almost at random. On each side of the street was, even into the present century, a very formidable channel, or kennel, as it was formerly written, into which, in heavy rains, the badly-scavaged street dirt was swept, often demanding a good leap from one who wished to cross in a hurry. These “kennels” emptied themselves into the gratings, which were not unfrequently choked up, and the kennel was then an utter nuisance. At the present time the channel is simply a series of stone work at the edge of the footpaths, blocks of granite being sloped to meet more or less at right angles, and the flow from the inclination from the centre of the street to the channel is carried along without impedimen or nuisance into the gully-hole.
The gully-hole opens into a drain, running, with a rapid slope, into the sewer, and so the wet refuse of the streets find its vent.
In many courts, alleys, lanes, &c., inhabited by the poor, where there is imperfect or no drainage to the houses, all the slops from the houses are thrown down the gully-holes, and frequently enough blood and offal are poured from butchers’ premises, which might choke the house drain. There have, indeed, been instances of worthless street dirt (slop) collected into a scavager’s vehicle being shot down a gully-hole.
The sewers, as distinct from the drains, are to be divided principally into three classes, all devoted to the same purpose—the conveyance of the underground filth of the capital to the Thames—and all connected by a series of drains, afterwards to be described, with the dwelling-houses.
The first-class sewers are found in the main streets, and flow at their outlets into the river.
The second-class sewers run along the second-class streets, discharging their contents into a first-class sewer; and
The third-class sewers are for the reception of the sewage from the smaller streets, and always communicate, for the voidance of their contents, with a sewer of the second or first description.
As regards the destination of the sewers, there is no difference between the Middlesex and Surrey portions of the metropolis. The sewage is all floated into the river.
The first-class sewers of the modern build rarely exceed 50 inches by 30 in internal dimensions; the second class, 40 inches by 24; the third, 30 inches by 18.
Smaller class or branch sewers, from No. 4 to No. 8 inclusive, also form part of the great subterranean filth-channels of the metropolis. It is only, however, the three first-mentioned classes which can be described as in any way principal sewers; the others are in the capacity of branch sewers, the ramifications being in many places very extensive, while pipes are often used. The dimensions of these smaller sewers, when pipes are not used, are—No. 4, 20 inches by 12; No. 5, 17½ inches by 10½; No. 6, 15 inches by 9; No. 7, 12 inches by 7½; and No. 8, 9 inches by 6.
These branch sewers may, from their circumscribed dimensions, be looked upon as mere channels of connection with the larger descriptions; but they present, as I have intimated, an important part of the general system. This may be shown by the fact, that in the estimates for building sewers for the improvement of the drainage of the city of Westminster (a plan, however, not carried out), the estimated, or indeed surveyed, run of the first class was to be 8118 feet; of the second class, 4524 feet; of the third, but 2086 feet; while of the No. 5 and No. 6 description, it was, respectively, 18,709 and 53,284 feet. The branch sewers may, perhaps, be represented in many instances as public drains connecting the sewer of the street with the issue from the houses, but I give the appellation I find in the reports.
The dimensions I have cited are not to be taken as an average size of the existing sewers of the metropolis on either side of the Thames, for no average size and no uniformity of shape can be adduced, as there has been no uniformity observed. The sewers are of all sizes and shapes, and of all depths from the surface of the streets. I was informed by an engineering authority that he had often seen it asserted that the naval authorities of the kingdom could not build a war-steamer, and it might very well be said that the sanitary authorities of the metropolis could not build a sewer, as none of the present sewers could be cited as in all respects properly fulfilling all the functions required. But it must be remembered that the present engineers have to contend with great difficulties, the whole matter being so complicated by the blunderings and mismanagement of the past.
The dimensions I have cited (because they appear officially) exceed the medium size of the newer sewerage, the average height of the first class being in such sewers about 3 feet 9 inches.
Of the width of the sewers, as of the height, no precise average can be drawn. Perhaps that of the New Palace main, or first-class sewer, 3 feet 6 inches, may be nearest the average, while the smaller classes diminish in their width in the proportions I have shown. The sewers of the older constructions nearly all widen and deepen as they near the outlet, and this at no definite distance from the river, but from a quarter of a mile or somewhat less to a mile and more. Some such sewers are then 14 feet in width; some 20 feet, and no doubt of proportionate height, but I do not find that the height has been ascertained. For flushing purposes there are recesses of greater or less width, according to the capacity of the sewer, where sluice-gates, &c., can be fixed, and water accumulated.
Under the head of “Subterranean Survey of the Sewers,” will be found some account of the different dimensions of the sewers.
The form of the interior of the sewers (as shown in the illustrations I have given) is irregularly elliptical. They are arched at the summits, and more or less hollowed or curved, internally, at the bottom. The bottom of the sewer is called the “invert,” from a general resemblance in the construction to an “inverted” arch. The best form of invert is a matter which has attracted great engineering attention. It is, indeed, the important part of the sewer, as the part along which there is the flow of sewage; and the superior or inferior formation of the invert, of course, facilitates or retards the transmission of the contents.
A few years back, the building of egg-shaped, or “oviform” sewers, was strongly advocated. It was urged that the flow of the sewage and the sewer-water was accelerated by the invert (especially) being oviform, as the matter was more condensed when such was the shape adopted, while the more the matter was diffused, as in some of the inverts of the more usual form of sewers, the less rapid was its flow, and consequently the greater its deposit.
What extent of egg-shaped sewers are now, so to speak, at work, I could not ascertain. One informant thought it might be somewhere about 50 miles.
The following interesting account of the velocities of streams, with a relativeness to sewers, is extracted from the evidence of Mr. Phillips:—
“The area of surface that a sewer will drain, and the quantity of water that it will discharge in a given time, will be greater or less in proportion as the channel is inclined from a horizontal to a vertical position. The ordinary or common run of water in each sewer, due from house drainage alone, and irrespective of rain, should have sufficient velocity to prevent the usual matter discharged into the sewer from depositing. For this purpose, it is necessary that there should be in each sewer a constant velocity of current equal to 2½ feet per second, or 1¾ mile per hour.” Mr. Phillips then states that the inclinations of all rivulets, &c., diminish as they progress to their outfalls. “If the force of the waters of the river Rhone,” he has said, “were not absorbed by the operation of some constant retardation in its course, the stream would have shot into the Bay of Marseilles with the tremendous velocity of 164 miles every hour. Even if the Thames met with no system of impediments in its course, the stream would have rushed into the sea with a velocity of 80 feet per second, or 54½ miles in an hour.... The inclinations of the sewers of a natural district should be made to diminish from their heads to their outfalls in a corresponding ratio of progression, so that as the body of water is increased at each confluence, one and the same velocity and force of current may be kept up throughout the whole of them.”
Mr. Phillips advocates a tubular system of sewerage and drainage.
The main sewer, which has lately called forth the most public attention and professional controversy, is that connected with the new Houses of Parliament, or as they are called in divers reports and correspondence, the “New Palace at Westminster.”
The workmanship in the building of the sewers is of every quality. The material of which some of the older sewers are constructed is a porous sort of brick, which is often found crumbling and broken, and saturated with damp and rottenness, from the exhalations and contact of their contents. The sewers erected, however, within the last twenty, and more especially within the last ten years, are sometimes of granite, but generally of the best brick, with an interior coating of enduring cement, and generally with concrete on their exterior, to protect them from the dampness and decaying qualities of the superincumbent or lateral soil.
The depth of the sewers—I mean from the top of the sewer to the surface of the street—seems to vary as everything else varies about them. Some are found forty feet below the street, some two feet, some almost level! These, however, are exceptions; and the average depth of the sewers on the Middlesex side is from twelve to fourteen feet; on the Surrey side, from six to eight feet. The reason is that the north shores of the metropolis are above the tide level, the south shores are below it.
An authority on the subject has said, “The Surrey sewers are bad, owing principally to the land being below tide level. They were the most expensively constructed, because, perhaps, in that Commission the surveyors were paid by percentage on the cost of works. When it was proposed, in the Westminster Commission, to effect a reduction of four-fifths in the cost, it was like a proposition to return the officers’ salaries to that extent, if they had been paid in that way.”
The reader may have observed that the official intelligence I have given all, or nearly all, refers to the “Westminster and part of Middlesex” Commission, and to that of the “Surrey and Kent.” This is easily accounted for. In the metropolitan districts, up to 1847, the only Commission which published its papers was the Westminster, of which Mr. L. C. Hertslet had the charge as clerk; when the Commissions were consolidated in 1847, he printed the Westminster and Surrey only, the others being of minor importance.
I may observe that one of the engineers, in showing the difficulty or impossibility of giving any description of a system of sewerage, as to points of agreement or difference, represents the whole mass as but a “detached parcel of sewers.”
The course of the sewers is in no direct or uniform line, with the exception of one characteristic—all their bearings are towards the river as regards the main sewers (first-class), and all the bearings of the second-class sewers are towards the main sewers in the main streets. The smaller classes of sewers fill up the great area of London sewerage with a perfect network of intersection and connection, and even this network is increased manyfold by its connection with the house-drains.
There is no map of the general sewerage of the metropolis, merely “sections” and “plans” of improvements making or suggested, in the reports of the surveyors, &c., to the Commissioners; but did a map of subterranean London exist, with its lines of every class of sewerage and of the drainage which feeds the sewers; with its course, moreover, of gas-pipes and water-pipes, with their connection with the houses, the streets, the courts, &c., it would be the most curious and skeleton-like map in the world.