You can create a flow path for a catchment that is based on the surface elevations and a manually selected hydraulically most distant point.
This command is useful for evaluating a few different flow paths before selecting one to use for analysis. For example, there could be a few equally appropriate, but different, flow path solutions for wooded areas, undeveloped land with many different features (rocks, ponds, and walls), or TIN that is not well-defined (such as if there are large gaps between TIN points or small aberrations that conflict with the general trend of the surface).
A catchment can have only one flow path, and many catchments defined from surfaces will already have a flow path defined for them as part of the catchment creation process. If a flow path already exists for the catchment, this command edits the flow path based on the hydraulically most distant point that you select. Any existing flow segment data that exists for the current flow path will be overwritten.
To create a flow path, you specify an upstream hydraulically most distant point and the same algorithm that is used in the Water Drop command is used to create a flow path. Flow segment slopes are based on the surface, but are not dynamically linked to it.
- If you have not done so already, create a catchment from a surface. Note: This command cannot be used on catchments created from objects unless you first use the Flow Segment vista and select a surface using the Select Reference Surface button. In that case, the Create Flow Path From Surface command produces a valid flow path if the point picked for the new flow path creates a path that flows down through the current Discharge Point location.
- Click Analyze tab
Ground Data panel Flow Paths drop-down 
Create Flow Path From Surface. - Select the catchment.
- Select the hydraulically most distant point.