A catch basin is a part of a storm drain or sewer system which is designed to trap debris so that it cannot enter the drainage pipes. Catch basins are a large scale version of the traps used in home drains to accomplish a similar function. Most municipal sewer and storm drainage systems use catch basins, and the design is basically the same all over the world, with a few small variations.
Catch basins have a wide sloping inlet which collects runoff, assuring that even when high volumes of water are being dumped into the system, there is minimal overflow. The inlet opens to a pipe which is covered with a grating. The grating traps large debris, preventing it from entering the piping. As water floods the catch basin, small particles which slip through the grate settle to the bottom. Drainage pipes are located above the bottom of this vertical pipe, ensuring that the water which flows into the drains is clear of sediment.