About Analyzing and Sizing a Gravity Pipe Network

You can use the Analyze Pipe Network wizard to resize pipes and reset inverts and to compute the energy and hydraulic grade lines according to HEC-22 2009 standards.

You can use this utility to:

Following is a before and after example of analysis results for a pipe network shown in profile view.

Pipe network before resizing Pipe network after resizing

There are two analysis types you can select: Resize Pipes and Reset Inverts and Compute Energy and Hydraulic Grade Lines.

Selecting both options applies the resulting properties, including the computed energy and hydraulic grade values, to the affected parts.

The calculations are based on the Urban Drainage Design Manual, Hydraulic Engineering Circular No. 22 (HEC-22), Third Edition, published by the U.S. Department of Transportation Federal Highway Administration.

Workflow Prerequisites

You can begin the workflow for sizing pipes after the following prerequisites are established.

Specifying Default Settings

Settings that must be specified manually for the tributary areas, structures, and pipes, or which are used as values in the analysis calculations, can be pre-established as defaults in the Analyze Gravity Network Default Settings dialog box. You can access this dialog box from the General page of the wizard.

Pipe Network Part Replacement

The Analyze Gravity Network wizard checks the current part catalog for replacement parts. If a required part size is in the catalog but does not exist in the current part list, then it is added to the current part list after the parts are replaced.

If the analysis determines that a different part size is required, that size will be queried from the original family of the pipe, and if the required size does not exist in that family, other part families that are used in the pipe network will be queried from. This may result in the material of one pipe being changed for a different material (but only if the other material is already used in the pipe network).

If... and if... then...
the original part is an 18 inch concrete pipe and the analysis determines that a 12 inch pipe can be used a 12 inch concrete pipe exists in the part catalog the 12 inch concrete pipe will be used
the original part is an 12 inch concrete pipe and the analysis determines that a 10 inch pipe can be used a 10 inch concrete pipe does not exist in the part catalog then other part families that are used in the pipe network will be queried from for a 10 inch pipe
Note: Notifications are not made when the material of a pipe is changed for a different material in order to match the recommended size. To review the pipe materials, you can output a pipe report or create a table in the drawing that includes a column to show the pipe material.

Post-Sizing Refinements

  • After applying the results to a pipe network to which pipe rules have been applied, it is recommended that you review the pipes in Prospector to see if the rules have been broken.
  • The outfall structure location and/or elevation may need to be modified to meet the desired cover value.