Bankfull Extent

The Stage Slider Tool allows for an interactive method of modeling the effect of changing the stage-height of a stream based on the topography. The Stage Slider tool can be used to identify residual pools, bars, wetted perimeters, bankfull-stage, and model the effects of flooding outside of the channel.

As part of the Topo Processing workflow, the stage slider tool is used to create a wetted perimeter polygon (WaterExtent) and bankfull polygon.

Steps

1. Make sure you have Detrended the Topographic DEM.

2. Click on CHaMP Toolbar\Topo Processing\Create Wetted and Bankfull Polygons. The Stage Slider Panel will open.

3. Make sure the correct Survey Geodatabase is open.

4. Click the Reference Points button. The slider will be moved to the mean elevation (“best fit”) of the reference points. For example, when creating the Water Extent polygon, use the Projected/EdgeofWater_Points feature class in the survey geodatabase. The slider will move to the average elevation of the Edge of Water points to serve as a starting place. Click OK when you have selected the Reference Points layer.

5. Click the Refresh button.

6. The panel will populate with a histogram of the elevation values of the Detrended DEM (the units are meters, but the values are relative to an arbitrary

7. Use the Slider Bar to raise and/or lower the stage elevation. The Detrended DEM in the map window will change accordingly. Use this to visually fit the wetted area to the set of reference points (i.e. edge of water points, bankfull points).

8. When the wetted area looks good, click the Save Polygons button at the bottom of the Stage Slider Panel.

   • Select the Type of Polygon to save (WaterExtent or Bankfull).
   • Leave the island/donut filters at the default settings for best results.
   • Click OK to save the Polygon.

Remember to use this process to create both a Water Extent polygon and a Bankfull Polygon.

Review and Edit the Extent Polygons

Use the “Editor” toolbar to edit the Water Extent and Bankfull polygons.

1. Remove tiny artificial holes within the polygons that you know are not accurate with the site water extent:

   1. Double Click on the polygon to show the vertices.

   2. Zoom in to one end of the polygon.

   3. Pan across the polygon and Scan it for tiny triangular or square holes using. You should be able to see the vertices inside the polygon.

   4. Use the Delete Vertex tool to remove these small, artificial donuts.

2. Open the attribute table of the WaterExtent and remove any polygons that have very small areas (delete them during an editing session). Do the same for the Bankfull polygon.

When you have finished creating and editing the Water Extent and Bankfull Polygons, you may proceed to Digitizing Channel Units.