London Labour and the London Poor, Vol. 2

by Henry Mayhew

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.