You can model drainage areas by using existing surface data or polyline data to create catchments.
A catchment object is comprised of a boundary and a flow path. The boundary represents the watershed area that produces the runoff. The flow path represents the Time of Concentration data for the runoff flow from the catchment area. This Time of Concentration data can be defined by using the NRCS (SCS) TR-55 method or it may be user-defined.
Creating Catchments from Surfaces
If existing surface data is available, you can define a catchment and flow path from this surface data.
You may optionally use the Water Drop command to check how AutoCAD Civil 3D would calculate the flow path from the surface. If this command does not produce the desired results, due to surface irregularities such as localized pits or triangulation issues, you may opt to use the Create Catchment from Object command and select a manually drawn flow path.
Creating Catchments from Objects
If existing surface data is not available, you can define a catchment and flow path from polylines. If the polylines have elevation data, you can use that data for the flow path slope, or you can edit the slopes of the flow path segments later by using the Flow Segments vista.
Topics in this section
- Creating Catchments from Surfaces
You can create a catchment based on the terrain of a specified surface.
- Creating Catchments from Objects
You can create a catchment that uses a polyline as its boundary and a polyline as its flow path.
- Editing Catchment Properties
Use the Catchment Properties dialog box to specify a reference pipe network structure for a catchment, the runoff coefficient, the time of concentration method, and the catchment style.
- Editing Catchment Styles
Catchment styles control the display of catchment boundary and flow path, as well as the marker styles for the catchment and flow path points.
- Editing Catchment Feature Settings
Specify default settings for catchments in the feature and command settings.