Thalweg

The Thalweg Tool creates a polyline that represents the thalweg of the stream. This thalweg line is not directly derived from the thalweg points (wg) collected in the field, although they should generally be in agreement if these points were collected properly. The algorithm used to generate the thalweg is based on a cost path analysis of the DEM (using distance and depth).

Steps

1. Make sure the Topo Points layer contains one inflow (coded ‘in’) and one outflow (coded ‘out’) point. These two points must lie on the DEM.
2. Open Create a Thalweg in the Workflow Manager.
3. Make sure the correct Survey Geodatabase is open.

4. Specify the following parameters:

   • Code Field: The Field within Topo Points that contains the Description codes. For most CHaMP surveys, this will correctly auto-populate to DESCRIPTION.
   • Inflow Code: Code used to describe the inflow point. For most CHaMP surveys, this should be set to in.
   • Outflow Code: Code used to describe the outflow point. For most CHaMP surveys, this should be set to out.
   • Pool Weight: Used to reduce the “cost” of placing the thalweg in pools or deep segments of the stream. Increase this value if the thalweg tends to cut off meanders or curves in highly sinuous channels.
   • Smoothing Tolerance (m): Distance used to determine the amount of line smoothing applied to the thalweg. Larger values will produce a smoother line, but will reduce the amount of detail (i.e. curves).

5. Click OK to run the tool.

6. Inspect the thalweg. If there are errors or problems with the output, consider re-running the Thalweg tool and changing the pool weight or smoothing tolerance values. Otherwise, manually edit the thalweg as needed.

After you have generated and checked the Thalweg, you may proceed to [generate wetted and bankfull channel centerlines.

Troubleshooting

• Make sure the Editor is turned off when running the tool.