1. Basic Hydrology & Hydraulics: DES 601
Module 14
Closed Conduit Flow

2. Closed Conduits
A closed conduit is a conduit (culvert, storm sewer) that has the conduit crown as the upper limit of flow – hence it behaves as a pipe under pressure
The HDM uses Manning’s equation as the loss model for closed conduits
Module 14

3. Hydraulic Grade Line (HGL)
Total energy line is called energy grade line (EGL)
EGL = h + p/g + V2/2g
Line that is sum of elevation and pressure energy is called hydraulic grade line (HGL) HGL = h + p/g
For pipes flowing full, EGL and HGL are parallel if pipe diameter does not change.
The invert elevation is called the flowline in the HDM
Module 14

4. HGL illustration
HW = headwater
TW = tailwater
Module 14

5. Energy Equation
The slope of the energy grade line is the friction slope in Manning’s equation
Thus the energy equation for the figure is
Module 14