What term denotes the elevation at a catch basin, manhole, or drop inlet grate?

• A. Rim Elevation
• B. Invert Elevation
• C. Deck Elevation
• D. Grate Elevation

Answer: (A)

Rim elevation is the elevation of the top edge of the inlet opening—the rim where the grate sits. This height defines how high the surface water must rise before entering the catch basin, manhole, or drop inlet, and it ties to the finished grade around the inlet. Invert elevation, by contrast, is the bottom interior level where flow begins inside the structure, used for calculating flow paths. Deck elevation refers to the top surface level of a structure like a bridge deck, not the inlet opening. Grate elevation would describe the height of the grate itself, but the standard term for the top-of-opening height is rim elevation.