When you get to the Cross Sections and IB Nodes, STOP. to import the Civil-3D-geometry-export you created.

In the HEC-RAS Geometry Data editor, use File, Import Geometry Data., GIS Format.

The finished sample lines should all start on the left and run to the right. After you select the alignment, a toolbox appears where you can choose to create the sample lines from polylines. They should cross (not end at or short of) the centerline. We will address the downstream to upstream hydraulic calculations later. Having it point downstream is important so that the cross sections and banks read correctly from left to right looking downstream.

Create a Civil 3D alignment from the polyline, and use the Reverse Alignment Direction tool if necessary so that the stations increase going downstream. Draw a stream alignment polyline (direction is not important).

Start with a ground surface that completely encompasses both the river alignment and the cross sections. But the general idea works with earlier Civil 3D and HEC-RAS 4. Note: These were written toward Civil 3D 2016 and HEC-RAS 5.

Civil 3d hec ras