Detrend

Detrending is a process that removes the overall valley slope of the stream channel from the DEM. The edge of water points are used to approximate the valley slope and create a “detrending surface” and used to change the DEM from an ‘inclined’ position to a ‘level’ position. During this process, the channel topography remains intact and can be used to model the effects of changing the stage-height of the stream.

Steps

1. Open Detrend a DEM to Remove the Valley Slope in the Workflow Manager.
2. Make sure the correct Survey Geodatabase is open.
3. Make sure Detrending Method parameter is set to Water Elevation Points
4. Click OK to run the tool.
5. The Detrended DEM will be added to the map.
6. Briefly review the Detrended DEM. In general, pools (channel features with low relief) should be blue, and banks should be green.

Advanced Method

For advanced situations, you can opt to use a different surface to detrend your DEM. For example, a dry or partially-dry site could use a surface generated from the bankfull elevations. Please consult a CHaMP Analyst before using this option.

Troubleshooting

• Make sure other ArcGIS programs are closed (i.e. ArcCatalog).
• Use the Clear Workspace Tool to remove extra processing data that might be causing the error.
• Manually delete the Detrended raster dataset in the Survey Geodatabase, if it exists.
• Close and Restart ArcMap.