Hydraulic and Energy Grade Lines (HGL and EGL)

Stormwater and Sewer Networks

The EPA SWMM engine used by Devotech iDAS calculates the HGL at the nodes. To display the HGL and EGL in the Civil 3D profile view, the pipe HGL and EGL values must be calculated and written into the pipe properties. The formulas below are used by Devotech iDAS for the calculations. The symbols used in the formulas are as follows:

v – velocity [m/s]

g – acceleration of gravity [m/s2].

1) STEADY FLOW AND KINEMATIC WAVE

Pipe HGL = Pipe Invert + Flow Depth (this calculation assumes steady flow in the system).

Pipe EGL = Pipe HGL + v2 / 2g.

2) DYNAMIC WAVE

a) If Pipe Invert + Flow Depth > Structure HGL, then

Pipe HGL = Pipe Invert + Flow Depth

Pipe EGL = Pipe HGL + v2 / 2g.

b) If Pipe Invert + Flow Depth < Structure HGL, then

Pipe HGL = Structure HGL

Pipe EGL = Pipe HGL + v2 / 2g.

The image below illustrates the various scenarios described above. Note that the Kinematic Wave behaves similarly to Steady Flow.

An example of the HGL and EGL in the Civil 3D profile view:

Although the HGL and EGL are properties of the pipe in Civil 3D, they are also displayed through the structures. Users do not have an option to switch off the HGL and EGL at the structure.

If multiple pipes are connected to a structure, Civil 3D displays the highest HGL and EGL at the structure. Users do not have an option to change this setting or switch it off (switching off the pipe in the profile view properties window also does not help). The image below displays this situation:

If there is no flow in the pipe, the HGL and EGL are not displayed correctly at the structures, see the image below. Unfortunately, there is no settings in Civil 3D which can change this behavior.

The HGL and EGL lines can be switched off by freezing the following layer:

Stormwater network:

It will also switch off the HGL and EGL lines form the profile view legend:

Before:

After:

Sewer network:

It will also switch off the HGL and EGL lines form the profile view legend:

Before:

After:

Water Networks

The EPANET engine used by Devotech iDAS provides the following results for nodes:

To display the HGL and EGL in the Civil 3D profile view, the pipe's HGL and EGL values must be calculated and written into the Pipe Properties. The following formulas are used by Devotech iDAS for calculations:

Pipe HGL = Node Elevation + Node Pressure = Node Total Head

Pipe EGL = Pipe HGL + v2 / 2g,

where: v – velocity [m/s]

g – acceleration of gravity [m/s2].

The HGL and EGL lines can by switched off by freezing the following layer:

It will also switch off the HGL and EGL lines form the profile view legend:

Before:

After: