You can use the Catchment Properties tab to change the Reference Pipe Network Structure, the Runoff Coefficient, the Time Of Concentration Method, and the Time Of Concentration (if the method is user-defined). The Catchment Properties tab also displays several read-only properties for the catchment.
- 2D Area of Catchment
- Discharge Point
- Reference Pipe Network
- Reference Pipe Network Structure
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Optionally specifies the pipe network structure to use as a reference for the catchment.
NoteCatchments 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. - Catchment Group Name
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Displays the group in which the catchment was created. To change the catchment group, you can use the Move To Catchment Group command.
- Reference Surface
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Displays the surface upon which the catchment area was calculated. If the catchment was creating using the Create Catchment From Object command, this value is <none>.ImportantThe 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.
- Runoff Coefficient
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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.
The following notes apply to the Sheet Flow, Shallow Concentrated Flow, and Channel Flow sections.
- If the Time Of Concentration Method is set to User-Defined, then the Sheet Flow, Shallow Concentrated Flow, and Channel Flow sections are not shown in this dialog box.
So that all flow segment data can be transferred to Storm and Sanitary Analysis in the STM file, the number of flow segments per flow type is limited to three. A maximum of three Sheet Flow, three Shallow Concentrated Flow, and three Channel Flow segments are allowed for any given flow path.
By default, flow paths are created with the number of segments as specified in the catchment feature settings. You can use the Edit Flow Segments command to add additional segments of any of the three types to a flow path after creation.
- Time Of Concentration Method
- Time Of Concentration
- Hydraulically Most Distant Point
- Hydraulically Most Distant Length
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Displays the distance between the specified discharge point and hydraulically most distant point.
This length may not be the longest measurable distance between any two points within a catchment; it can be shorter.
Water moves through a watershed as sheet flow, shallow concentrated flow, swales, open channels, street gutters, storm sewers, or some combination of these. The hydraulically most distant length represents these flows along a path where "distant" relates to time rather than length.