Hydraulic Grade Line

The surface or profile of water flowing in an open channel or a pipe flowing partially full. If a pipe is under pressure, the hydraulic grade line is at the level water would rise to in a small vertical tube connected to the pipe.

See Also: Energy Grade Line (EGL) United States Pharmacopeia (USP) WFI Slope Conventional Filtration Turnover Alkylaryl Sulfonate Alkylbenzene Sulfonate (ABS) Hypolimnion Direct Filtration Energy Grade Line (EGL) Epilimnion