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HEC-RAS Data from Civil 3D

Civil 3D can be a great way to assemble stream centerlines and cross-sections for HEC-RAS.  A few "gotcha's" are possible, however, and one should know that the Civil 3D point of view (i.e. stationing, direction) tends to be that of roadways.  The river point of view is often opposite.

This spreadsheet takes a .geo file of RAS data exported from Civil 3D and flips it around so that it imports correctly into HEC-RAS.  See details below.


Tips for creating RAS geometry in Civil 3D are given below, and sample drawing for download. Here is a screenshot of the spreadsheet with button to execute macro:

Excel macro window.



To use the RASflipper macro, an export file of RAS data from Civil 3D is needed.  These text files are named with a ".geo" extension.  Draw stream centerlines in Civil 3D from downstream to upstream (opposite of RAS).  Example drawings and export files are available.  The RAS files (in show how the imported geometry looks in RAS, both before and after using the RASflipper macro.

BalchCreekForRAS.dwg         BalchCreekForRASbeforeRchLines.dwg
  (terrain data for the Civil 3D drawings)

BalchCreekFromCAD.geo       BalchCreekFromCADFlipt.geo

Here's a screenshot of the downstream end of the Balch Creek drawing. Note scroll bar:

CAD drawing of stream channel

In the drawing above, the stream centerline has been drawn from downstream to upstream. Note that the stationing starts from zero at the downstream end (good for RAS).  The cross-sections can be drawn in any order and any direction.  The two reach length lines can be drawn in any order, starting either upstream or downstream.  The left bank reach length line was drawn from upstream to downstream, so the highest station is at the downstream end.  The right bank reach length line was drawn opposite.  But the stationing of the reach length lines doesn't matter because the reach lengths are determined by the difference between cross-sections.

Also, the locations where the reach length lines intersect the cross-sections is set to the bank station in RAS.  Since generally we want the overbank flow reach length to be further out from the bank, these bank stations will need to be adjusted in RAS.  It is most convenient to have Civil 3D compute all the flow reach lengths, and then in RAS move the bank stations, using the Graphical Cross-Section editor.

Below is a screenshot of the export window in Civil 3D (2014 version):

Export window from Civil 3D.

The river banks (reach length lines) are optional.

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