Catch Basins

It is customary to place a catch basin at the corner of the curb. For additional objections to this location, see § 506.

The number and capacity of catch basins will depend upon the area drained, the amount of rain, the grade of the gutter, etc. On streets having light or level longitudinal grades catch basins may be constructed at intervals along the gutter as the circumstances require.

Form of Cover.

When a catch basin or sewer manhole is located in a pavement, the shape and the surface of the cover require attention. The upper surface of the cover and also of its frame should be covered with projections to afford a good foothold and to prevent it from wearing slippery: The best form for the frame depends upon the material of the pavement. For macadam and asphalt the round frame is best, since it offers least obstruction to traffic; the next best form is a square frame set diagonally to the line of travel. For a pavement made of bricks or stone blocks, the frame set with its sides parallel to the length of the street is best, because the bricks or blocks can be most closely fitted against this form. In Europe and in many American cities, it is customary to use only a square form, and to set it diagonally in macadam and asphalt pavements, and square in stone block and brick.

Often water-gate or stop-box covers are round in plan and have a convex surface, although the convex surface is very objectionable. The better form is a cover round in plan with a flat recessed top set flush with the pavement. Preferably the portion below the ground should be provided with a cast screw for adjusting the height. This form may be had of dealers in street-drainage goods.

The Inlet.

In a general way, there are stone and cast-iron inlets. The former consist either of an opening between a stone cover and a stone floor, or a slot through the stone curb (see Fig. 98,

page 338). This form is usually entirely open, but it is sometimes barred with one or two horizontal iron rods.

There are a great variety of cast-iron inlets on the market, which may be classified as being straight or curved, and also as having a vertical or a horizontal opening. Fig. 101, page 341, shows an un protected straight vertical inlet. Sometimes the opening is pro tected by one or more horizontal or vertical rods. The latter are the better, as they offer greater protection against the entrance of debris—particularly sticks and boards. Fig. 102 shows a vertical front curved for a corner, having vertical bars. Fig. 103 and 104 are two styles of a form having both a vertical and a horizontal opening. Notice that Fig. 100, page 339, has only a horizontal open ing. A horizontal opening is not so good as a vertical one, since the former is easily stopped by a few leaves, and the accumulation of water makes the stoppage more complete; while the barred vertical opening is less easily obstructed. and as the water rises it can pour over the obstruction already formed.

Inlet without Catch Basin. It

is sometimes desirable to connect two or more inlets to one catch basin—for example, see 507. There are various forms of such inlets on the market and many cities have their own special designs. Fig. 105, page 342, shows the form of inlet used in such a case at Omaha, Nebraska.* The entrance A is reduced by cast ribs to three open ings 6" X 9" at the top and 4-1" X 2" openings at the bottom. The section B is rectangular in plan at both top and bottom. The section C is rectangular at the top and circular at the bottom, and fits into the hub of a vitrified elbow. Fig. 106, page 342, shows a commercial form of inlet, which has an adjustable curb. It is made to fit various sizes of outlet pipe.