Create Catchment From Object Dialog Box

Use the Create Catchment From Object dialog box to define styles, flow path settings, and other parameters.

Catchment Name

Specifies the catchment name.

Description

Specifies an optional catchment description.

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.

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: 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.

Erase Existing Entities

Erases the existing polylines used to define the catchment and flow path.

Flow Path Tab

Note: If you do not select a flow path polyline at the start of the Create Catchment From Object command, the Time Of Concentration cannot be calculated and the TR-55 value will be zero. Unless you plan to create a flow path at a later time, specify the User-Defined method and enter the desired value.

Calculation Method

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

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.

Flow Path Slopes

Specifies how the slope of the selected flow path is determined.

• From Object: Uses the elevation values of the selected polyline for the flow path slopes.
• From Surface: Uses the elevation values of a selected surface for the flow path slopes.