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Wetted Centerline and Islands

The centerline tool generates a polyline representing the ‘geometric’ center of the wetted polygon (i.e. center of the stream). The centerline is an important component of CHaMP metric generation in that both site reach metrics (centerline length, sinuosity, gradient) and cross sections are derived from this feature.

You will need to run this tool twice: once for the wetted polygon centerline, and again for the bankfull polygon centerline.

Steps

Open CHaMP Toolbar/Topo Processing/Create a Centerline

  1. Generate Island Polygons:
    1. Make sure the correct Survey Geodatabase is open.
    2. Click Generate Island Polygons
  2. Verify Qualifying Islands:
    1. Make sure the islands are classified correctly (Qualifying or Non-Qualifying/bar)
    2. To chance an island’s qualifying status, use the Select Features Tool to select the island and click Classify current selection as Island(s) or Classify Current Selection As Non-Island(s).
  3. Generate Centerline:
    1. When you are satisfied with the status of the Islands, click the Generate Centerline button. > The tool may take a few minutes to complete processing. Do not click any buttons until the tool has completed.
  4. Inspect the output Centerline on the map. Make sure that:
    • The centerline stays within the Water Extent (or bankfull).
    • The centerline is generally smooth without sharp curves/kinks
    • The ends of the centerline` exit the channel correctly (are not skewed).
    • The centerlines of side channels start and end on the main centerline.
  5. If there are problems with the centerline, you may edit this feature manually.
    1. Right click Centerline in the Table of Contents and select Edit Features\Start Editing
    2. Double click on the centerline feature in the map to select it for editing.
    3. Modify the line vertices as needed to repair errors.
    4. Right click on the centerline feature on the map and select Finish Sketch
    5. End the Edit Session and save edits.

Troubleshooting

  • If you have processed several sites using the Toolbar, try clearing the Temporary Workspace.
  • Make sure the Editor is turned off when running the tool.
  • Make sure the Thalweg polyline is within the Water Extent Polygon for its entire length.
  • Make sure there is ONE and ONLY ONE Water Extent (or Bankfull) Polygon Feature.
  • The centerlines should pass around Qualifying Islands, and may pass across Non-Qualifying Islands/bars.
  • If an island crosses the top or bottom of the survey (i.e. island is not completely within the survey extent): Then you must manually digitize in the side channel centerline.
    1. Start an edit session,
    2. Using the Create Features Panel, select Side Channel.
    3. Digitize the feature along the center of the side channel. Make sure to stop just inside the survey extent and the other end is snapped to the main centerline.
    4. Stop the Edit Session and Save Edits.

After you have created and checked your centerlines, you may proceed with Generating Cross Sections.

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