Troubleshooting Watershed Analysis

The following suggestions improve the setup of a watershed analysis so it's more likely to return watersheds.

When a watershed analysis doesn't identify a watershed, Drainage Design displays a message.

Reason	Solutions
Placing the outlet point for an analysis where there is not enough upstream flow accumulation to identify a watershed, or too far away from a ditch.	Use terrain themes to locate low levels where a ditch is likely to occur. For more information, see To theme terrain. Place the outlet point at a lower level so more upland area contributes to the watershed. Reduce ditch threshold to increase ditch generation density. Adjust grid spacing to find a larger watershed area. Grid Spacing and Ditch Threshold have a direct correlation to the size of the watershed the analysis may identify.
Selected road or region doesn't cross a ditch.	Select a longer road region to increase chances of locating a ditch crossing the road. Reduce ditch threshold to increase ditch generation density. Use terrain themes to check if the road runs along low levels. For example, a road drawn along a ridge line is unlikely to cross a ditch. For more information, see To theme terrain.

Reason

Solutions

Placing the outlet point for an analysis where there is not enough upstream flow accumulation to identify a watershed, or too far away from a ditch.

Use terrain themes to locate low levels where a ditch is likely to occur.
For more information, see To theme terrain.
Place the outlet point at a lower level so more upland area contributes to the watershed.
Reduce ditch threshold to increase ditch generation density.
Adjust grid spacing to find a larger watershed area.
Grid Spacing and Ditch Threshold have a direct correlation to the size of the watershed the analysis may identify.

Selected road or region doesn't cross a ditch.

Select a longer road region to increase chances of locating a ditch crossing the road.
Reduce ditch threshold to increase ditch generation density.
Use terrain themes to check if the road runs along low levels. For example, a road drawn along a ridge line is unlikely to cross a ditch. For more information, see To theme terrain.