Catch Basins

CATCH BASINS. The catch basin is a pit to receive the drainage from the surface of the street, in which is deposited the sand and other solid matter, and from which the water is discharged into the sewer or storm-water drain. A catch basin should fulfill the following conditions: (1). The inlet should offer the least possi ble obstruction to traffic, should have sufficient capacity to pass speedily all the water reaching it, and should not easily be choked by leaves, paper, straw, etc. The capacity below the outlet should be sufficient to retain all sand and road detritus and thus prevent it from reaching the sewer, and will depend upon the area drained and the intervals between cleanings. (3) The water level should be low enough to prevent freezing. (4) The construction should be such that the pit may be easily cleaned out. (5) The pipe connecting the basin with the sewer should have sufficient capacity, and should be so constructed as to be easily freed of any obstruction. (6) It is desirable that the outlet should be trapped so as to prevent floating debris from reaching the sewer. (7) If the catch basin discharges into a sewer which also carries house sewage, the end of the outlet pipe should be trapped to prevent the escape of air from the sewer to the street through the catch basin.

The Construction.

Catch basins are usually built of brick masonry, and plastered on the inside, at least up to the water line. Fig. 97, page 337, the standard of Champaign, Ill.,f is a good form. The opening of the inlet is protected by six half-inch iron rods. The several parts of the cast-iron top are 1 and inch thick; and the total weight of the castings is 162 pounds The pit requires 1,000 brick. The total cost of the catch basin when laid in 1 to 2 natural cement mortar is $17.00 to $19.00, including castings, excavation and the vitrified elbow.

Fig. 98, page 338, shows the standard catch basin of Prov idence, R. I.* This form differs from that shown in Fig 97 in the form of the inlet and of the trap for the outlet. The latter is made

of iron cast in a single piece, and is somewhat complicated in form, but a careful study of the two views shown in Fig. 98 will make the construction reasonably clear. The seal in Fig. 98 is better than that in Fig. 97; but the former is used only with storm water sewers and for such use the trap is sufficient. Not infre quently, the outlet of the catch basin is left untrapped; and sometimes an inlet is connected to a sewer without the inter vention of either a catch basin or a trap. This practice is likely to clog the sewer.

Fig. 99, page 339, is the standard for Milwaukee, Wis.* This diagram is presented to show (1) the form of the inlet, (2) the method of preventing floating debris from entering the outlet, and (3) the method of ventilating the sewer.

Fig. 100, page 339, shows the standard form in St. Pancras Vestry, London, England.f In England many earthenware catch basins or "gully pits" are used. Some of these forms are quite complicated. American engineers object to earthenware pits on account of (1) their limited size, (2) their great cost, and (3) their liability to be broken by the weight and jar of the street traffic.

Location.

The catch basin is usually placed near the curb with the cover in the sidewalk or the parking. It is objectionable to have the cover in the sidewalk, since (1) the cover itself is some thing of an obstruction to travel and is dangerous when it wears smooth or is covered with snow, (2) the clearing of the pit seriously interferes with the convenient use of the footway, and (3) in empty ing the pit the sludge is likely to be spilled on the footway, and at best the odor is offensive. In some cities these objections are elim inated by placing the inlet at the curb line and conducting the drain age to a catch basin near the center of the street, one basin serving for two or more inlets. Notice that the catch basin shown in Fig. 100 cleans out in the gutter.