Create Catchment From Surface Dialog Box

Use the Create Catchment From Surface dialog box to select the surface on which to base the catchment geometry and to define styles and other parameters.

Catchment Name
Specifies the catchment name.
Specifies an optional catchment description.
Specifies whether a catchment will exclude other catchments.

Exclusionary catchments exclude any other catchments whether the other catchments are exclusionary or not. If a catchment is exclusionary, its boundary (and flow path) can be modified either by existing catchments as it is being created or by new catchments as they are being created.

As a catchment is created, it will check all other catchments for two situations:

  • If another catchment is exclusionary, and if the new catchment has some (or all) of its boundary within it, the other exclusionary catchment will exclude the new catchment from itself.
  • If the new catchment is exclusionary, and if the other catchment has some (or all) of its boundary within it, the new catchment will exclude the other catchment from itself.
Catchment Group
Specifies the catchment group. Select a group from the list, click Create New to create a new group, or click Pick From Drawing to select a catchment in the desired group.
Specifies the surface on which to base the catchment and flow path. Select a surface from the list or click Select From Drawing to select a surface in the drawing.
Important: The surface associated with a catchment cannot be changed after the catchment is created. The catchment does not update dynamically if the surface changes after the catchment is created. However, you may select another surface to use for calculating flow paths when using the Edit Flow Segments command.
Reference Pipe Network

Displays the name of the pipe network that contains the pipe network structure you select in the Reference Pipe Network Structure list.

Reference Pipe Network Structure

Optionally specifies the pipe network structure to use as a reference for the catchment. An associated pipe network structure is not required to create a catchment, but it is required if you want to export the catchment to Storm and Sanitary Analysis later.

Note: Catchments can be associated with a single pipe network structure. The reason for making this association is to enable catchment data to be exported to Storm and Sanitary Analysis. When catchments are associated with a structure, they can be exported and converted into a Storm and Sanitary Analysis subbasin. With no association, however, catchment data cannot be exported.
Note: You can assign a pipe network structure to the catchment at any time by editing the Catchment Properties before running the EditInSSA or ExportToStormSewers commands.

Catchment Tab

Catchment Style
Specifies the style for the catchment. The default style is specified in the Catchment Feature Settings.
Catchment Layer
Specifies the layer for the catchment. The default layer is specified on the Object Layers tab of the Drawing Settings dialog box.
Catchment Label Style
Specifies the label style for the catchment area.
Flow Segment Label Style
Specifies the label style for flow segments.
Runoff Coefficient

Specifies the runoff coefficent for the catchment. Acceptable values are between 0.01 and 1.00. A runoff coefficient is used when calculating runoff with the Rational methods. This value is not used by AutoCAD Civil 3D; however, when you use the Edit in Storm and Sanitary Analysis command, it is exported as part of the catchment data so it can be used in Storm and Sanitary Analysis.

Flow Path Tab

Calculation Method
Specifies the calculation method to use for calculating the Time Of Concentration. Available methods are TR-55 and User-Defined.

Specifies a user-defined Time Of Concentration value. This field is enabled only if you select User-Defined from the Calculation Method list.

Note: When the Calculation Method is set to User-Defined, a flow path can have only one segment. You cannot use the Create Flow Segments command to add additional segments.
Draw Flow Path
Draws a flow path between the hydraulically most distant point in the catchment and the discharge point. This option is disabled and is always selected if you select TR-55 as the Calculation Method.
Note: You can define additional flow paths by using the Create Flow Path From Surface and Create Flow Path From Object commands. You can also define flow path segments by using the Edit Flow Segments command.