Analyze a Gravity Network in Civil 3D

Brian Johnson | Applications Expert

The Analyze Gravity Network feature in Civil 3D provides a way to resize pipes, reset inverts and computer the Hydraulic and Energy Grade Lines (HGL and EGL) utilizing the HEC-22 2009 standards.

This is an easy to use tool that functions directly inside of Civil 3D and is useful for analyzing gravity fed pipe networks without exporting and re-importing the runs.

Start the process by selecting the Analyze tab on the ribbon > Design panel > Analyze Gravity Network to launch the command. Next, select the pipe network to analyze.

A dialog will open and on the first page (General) and input will be needed to choose/set:

1. The outfall type
2. Tailwater condition
   1. Elevation
   2. (dc+D)/2
   3. Crown
   4. Normal depth
3. Analysis type
   1. Resize pipes and reset inverts
   2. Compute energy and hydraulic grade lines
4. Default Settings button
   1. Structure settings: controls inlet type, Grate dimensions, Local depression, and Curb opening dimensions.
   2. Pipe settings: controls min/max velocity, min cover, N-value and min crown drop
   3. Tributary Areas settings: min TOC, Known Flow, Road cross slope, Gutter cross slope, Gutter width and N-value, and Longitudinal slope.
   4. Graphical preview in profile: controls the color of the HGL, EGL, and new pipe size

The next page (Rainfall) requires IDF curve storm information for the location and can be uploaded via an .idf file. Select the Intensity table needed for the analysis.

The Structures page assigns values and settings for the associated structures in the network. Default settings can be applied from the Default Settings defined on the General page.

The Tributary Areas page shows the inlets of the network which contribute to the specified outfall and the catchments that have been defined for the inlets.

The Pipes page provides the values and settings for the pipes in the network. When this page is complete click on the Analyze button to analyze the network and see the results.

The Results page the options to:

1. Export the results to CSV and view in profile
2. Modify the Results
3. Apply the Results to the Network

The export to CSV results in the calculated results in a tabular format that can be opened in Excel.

Modify the Results takes you back into the dialog to adjust any of the values necessary.

Apply the Results to the Network will take you back to Civil 3D, the network will update accordingly with resized pipes and show the HGL and EGL in profile view.

Note: The HGL and EGL components must be turned on in the pipe style and profile view in order to see the resulting lines.

This is a great feature if you need to resize the pipes and reset inverts and compute the HGL and EGL to show in profile view on your drawings. There is a chapter in the Civil 3D Help that provides good information, I highly recommend investing the time to get familiar with it.