Analyse watersheds from an outlet point, an entire design road, or a region of a design road.
- Use terrain themes as needed to identify lower levels where a ditch is more likely to occur.
For more information, see To theme terrain.
- Adjust grid spacing or ditch threshold to improve precision or speed of watershed analysis.
- Click
. - To obtain results for smaller watersheds or for faster analysis of a large area, adjust grid spacing or ditch threshold in Analysis Settings.
- Follow the prompts in canvas to start one of the following watershed analysis methods:
- Outlet Point: Click to place a point at a low spot in the terrain. Then press Enter.
- Design Road: Click on a design road. Then press Enter to analyse the entire road.
To analyse a design road region, click to specify the start chainage and end chainage. Then press Enter.
Analysing a design road region improves performance and helps the analysis return a watershed.
- Click watersheds individually to display their asset cards.
Drainage Design uses Peak Flows (cms) value of Q100 (100-year flow) for culvert design solutions. Analysis supports two hydrology methods for Flow value: Rational or Regression; as well as supporting user-defined values. Choose a method from the watershed asset card.
If an analysis doesn't identify a watershed
Drainage Design displays a message if an analysis doesn't identify watersheds. Common reasons are:
- Placing the outlet point where there is not enough upstream flow accumulation to identify a watershed or placing it too far from a ditch. Change outlet placement or use terrain themes to find lower levels.
- Selecting a road or road region where no ditchs cross the road. Try extending shorter regions.
See Watershed Analysis Tips for more suggestions on refining an analysis.