From tests by W. W. Horner. Cubic feet per second ─────────┬───────────────────┬─────────────────── Slope in │ 0.42 │ 1.5 Per Ct. │ │ ─────────┼────┬────┬────┬────┼────┬────┬────┬──── Depth of │ 0.0│ 2│ 4│ 6│ 0│ 2│ 4│ 6 Sump, │ │ │ │ │ │ │ │ Inches │ │ │ │ │ │ │ │ Capacity,│ │ │1.27│ │ │ │ │ old │ │ │ │ │ │ │ │ style │ │ │ │ │ │ │ │ Capacity,│ 0.1│ 0.5│ 1.5│ 2.5│0.08│ 0.4│ 1.1│ 2.1 new │ │ │ │ │ │ │ │ style │ │ │ │ │ │ │ │ ─────────┴────┴────┴────┴────┴────┴────┴────┴────
─────────┬───────────────────┬─────────────────── Slope in │ 2.85 │ 4.5 Per Ct. │ │ ─────────┼────┬────┬────┬────┼────┬────┬────┬──── Depth of │ 0│ 2│ 4│ 6│ 0│ 2│ 4│ 6 Sump, │ │ │ │ │ │ │ │ Inches │ │ │ │ │ │ │ │ Capacity,│0.03│0.25│0.78│1.49│ │ │ │ old │ │ │ │ │ │ │ │ style │ │ │ │ │ │ │ │ Capacity,│0.03│0.28│0.87│1.62│0.02│0.15│0.45│ 1.0 new │ │ │ │ │ │ │ │ style │ │ │ │ │ │ │ │ ─────────┴────┴────┴────┴────┴────┴────┴────┴────
Gratings with horizontal bars will admit more water than gratings with vertical bars, but they will also admit more rubbish such as sticks, papers, leaves, etc., which serve to clog the sewers. Vertical barred gratings and gratings in the bottom of the gutter clog more quickly than other types. In the selection of the type of grating to be used a decision must be made as to whether it is more desirable to clean the sewer or catch-basin, or to flood the street as a result of clogged inlets. Where catch-basins are used or the sewers are large, horizontal bars are more satisfactory. The openings between bars should be small enough to prevent the entrance of a horse’s hoof or objects of sufficient size to clog the sewer. Four inches in the clear for vertical openings and 6 inches for horizontal openings are reasonable sizes.
The location of the inlets at the intersection of the two curb lines at a corner results in a lower first cost but on heavily traveled streets this may result in a higher maintenance cost than for other locations because of the concentration of traffic at street corners, hammering the inlet casting out of shape or position. Vehicles making short turns will tend to climb the curb and will intensify the wear upon the inlet. These objections can be overcome by the use of two inlets at each corner, set back far enough from the curb intersection to avoid interference with the cross-walks. This also makes it possible to raise the cross-walks without the use of gutters under them.