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.
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.