When working with an existing river basin DTM, the following workflow should depict the location where the 20 foot flood level will intercept with the original surface:
- Place linestrings along each bank of the river.
- Create features in the surface from the linestrings:
- Select File > Import > Surface - From Graphics
- Select Drape to Surface.
- Select Exclude from Triangulation.
- Move the features up 20 feet in elevation:
- Select Surface > Edit Surface > Transform Surface.
- Set Method to Relative.
- Set Elevation to 20.
- Original and Destination surfaces are the same.
- Display the features in the design file.
- Select Surface > View Surface > Features.
- Select the two features created in Step 2.
- Create a Decision Table that moves horizontally to intercept the surface.
- Create a single entry in the decision table that has a 0% slope and extends far enough horizontally so that it will intercept with the surface.
- Toggle on Seek Intersection and Construct Point.
- Select Surface > Design Surface > Apply Decision Table to run the horizontal decision table along the features created in Step 2.
- Add the intercept into the surface or select Generate Graphics Only.
Option: Instead of creating two features for the river banks, use a horizontal alignment along the river to create a single feature. Then apply the decision table off both sides.