What is catch basinin construction?

A catch basin collects surface water through an open grate and holds a sump below its outlet pipe to trap sediment. A manhole is an access structure with a solid cover, placed so crews can enter the pipe network for inspection and maintenance, and it does not take surface flow. They are counted the same way in a takeoff, each by depth class, but they carry different castings, details, and unit prices.

Subtract the lowest invert elevation from the rim elevation shown on the utility plan or structure schedule, then add the sump depth from the project detail. That total vertical dimension determines how many precast sections the structure needs and how much trench excavation and backfill it carries. Estimators group the results into depth classes, commonly 2 ft steps, because that is how precast suppliers and utility subs quote.

Typically the structure excavation, bedding, the precast base and riser sections, grade rings, the frame and grate, backfill, and final adjustment to grade after paving. The connecting storm pipe is not included; it is a separate lf takeoff. Watch the frame and grate spec closely, because a traffic rated curb inlet casting prices very differently than a pedestrian flat grate, even on structures with identical depth.