To Create Catchments From Surfaces

You can create a catchment based on the terrain of a specified surface.

The catchment's flow path can be created at the same time you create the catchment. It is drawn between the specified discharge point and the hydraulically most distant point that is calculated.

Tip: The Create Catchment From Surface command calculates the hydraulically most distant point based on the surface terrain. However, you can use the Create Flow Path From Surface command to select a different hydraulically most distant point to explore other options.

The flow path is created using the settings specified in the CreateCatchmentsFromSurfaces command settings.

The Create Catchment From Surface command only creates areas flowing to a point. For catchment areas flowing to a boundary, use the Create Catchment From Object command.

Click Analyze tab Ground Data panel Catchments drop-down Create Catchment From Surface.
Click in the drawing to specify the discharge point.
Use the Create Catchment From Surface dialog box to define the catchment properties and click OK.

If the input parameters result in a valid catchment, the catchment is created in the drawing using the specified catchment style.

If the input parameters do not result in a valid catchment or flow path, the AutoCAD Text Window may display the following errors:

Issue	Solution
A catchment is not created for the selected discharge point The specified location results in a catchment with no area	The calculation algorithm used may not result in a valid catchment for each selected discharge point. In order for this command to produce a catchment area, the surface triangle edges must form a channel that slopes toward the discharge point. It may be useful to run the Water Drop command and find a path that runs close to a location of interest, such as a location where you might want a catch basin or grate. Selecting a point along the path as the discharge point will typically yield a catchment area. If the command encounters a "flat edge" or small aberration that conflicts with the general trend of the surface leading to the discharge point, it will stop and a catchment will not be created. If the Create Catchment From Surface command does not work for a particular point, you may need to manually draw a polyline and use the Create Catchment From Object command. This may be the case if you are trying to get an area that flows to a property line or wetland boundary.

Issue

Solution

A catchment is not created for the selected discharge point

The specified location results in a catchment with no area

The calculation algorithm used may not result in a valid catchment for each selected discharge point.

In order for this command to produce a catchment area, the surface triangle edges must form a channel that slopes toward the discharge point. It may be useful to run the Water Drop command and find a path that runs close to a location of interest, such as a location where you might want a catch basin or grate. Selecting a point along the path as the discharge point will typically yield a catchment area.

If the command encounters a "flat edge" or small aberration that conflicts with the general trend of the surface leading to the discharge point, it will stop and a catchment will not be created.

If the Create Catchment From Surface command does not work for a particular point, you may need to manually draw a polyline and use the Create Catchment From Object command. This may be the case if you are trying to get an area that flows to a property line or wetland boundary.

To Create Catchments From Surfaces

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