Engineering Wonders of the World
Volume III

212 ENGINEERING WONDERS OF THE WORLD. WEIR CHAMBER AT HAMMERSMITH ROAD—THE LARGEST YET BUILT. . {Photo, E. Milner.) In times of heavy rain the surplus which the main sewer cannot carry flows over the weir wall into the storm-relief sewer, from which it is discharged into the Thames. On the south side the low-level, the high- level, and the EfTra sewers, totalling, exclusive of important branches, 27 miles, met at Dept- ford. Here the first was pumped, and the two second discharged by gravitation, into the out- fall sewer, which carried the sewage to Cross- ness. At Crossness all the sewage of South London, had to be pumped to a level at which it could be emptied into the Thames. These three south intercepting sewers may therefore all be considered as low-level. The general idea of the scheme was to separate the London area into strips, each of which, should drain into an intercepting sewer passing along its river-side boundary. The main sewers, running north and south at right angles to the intercepting, were themselves fed by a ramification of local sewers serving every individual street. Water emptied down a sink, whether in Chelsea, Hampstead, Holborn, or Shoreditch, would eventually find its way to Barking, just as water from the roofs of houses in Walworth, Dulwich, and Bermondsey would in like manner be delivered at Crossness. There was no escape from the sewer network. Sir Joseph Bazalgette based his calculations on a total population of 3,450,000 persons, and an average of 5 cubic feet (31| gallons) per day for every person. The inter- , ,, „ Storm Water. cepting and outfall sewers were designed to carry off 108,000,000 gallons per day in dry weather, allowing for the fact that the flow is much greater at some periods of the day than at others. Besides the actual sewage the rainfall had to be taken into consideration. The intercepting sewers and outfalls were