To Prepare Data to Export to HEC-RAS Format

1. In Autodesk Civil 3D, open a drawing that contains a ditch you would like to study, along with an existing ground surface.
2. Define the ditch centerline as an alignment. Be sure the chaining goes in the desired direction.
3. Create a sample line group with chainages at the desired section locations along the ditch centerline alignment.
   Note: For HEC-RAS analysis, be sure that the sample lines do not extend beyond the extents of the surface.
4. Optionally, create alignments or draw polylines to represent left and/or right ditch banks.
   Note: The bank locations appear in the HEC-RAS application as red dots on the sections. The left and right bank locations tell HEC-RAS where the Manning’s n values change for left, drainage channel, and right bank situations in the section. This effects the calculations and the level of water in the section.

BestPractice: It is recommended to use the same drawing for exporting data to be used in HEC-RAS that you use for importing data from HEC-RAS.