In my AU Class last week (Modeling Rivers, Channels, and Streams With AutoCAD® Civil 3D® 2010), I pointed out that the Channel subassemblies have their attachment points in the middle instead of at the stream bottom or channel invert.
In some cases, you might have a profile for bankfull elevation that would serve as a decent baseline profile, but most often, you will spend your time designing the channel bottom.
While you can certainly use generic links or any other combination of appropriate subassemblies to build a channel assembly, the prebuilt channel assemblies have a built-in parameter that would be useful for quantity takeoff and potentially even rendering- lining depth. It can also be nice to just have to manage on subassembly instead of several generic links.
One way you can generate a profile for the attachment point without doing too much extra work is to build a temporary corridor that generates one. This is same idea as the technique of making temporary corridors and surfaces for stream modeling and road widening.
1. Build a new assembly using the MarkPoint subassembly.
2. Figure out where the attachment point will be.
3. Using whatever AutoCAD method you prefer (I am trying to get in the habit of using dynamic input), move the MarkPoint to the right level.
4. Build a new corridor using only the MarkPoint assembly. It will be very skinny and might be hard to see at first. You might need to increase the frequency if your stream is very curvy.
5. Use the Profile from Corridor tool (on the contextual corridor tab) to extract a profile.
6. Have a look. Note that profiles extracted this way are not dynamic to the corridor.
7. Build a corridor for your channel using the stream centerline alignment and your newly extracted profile.
Since the extracted profile is not dynamic, you could also use the same method as described in my post about making temporary corridors and surfaces for stream modeling. Instead of using just a marked point, you could attach LinkWidthAndSlope or LinkSlopeToSurface and build a flat corridor, then a surface, and sample that surface on to the profile view for use as a baseline.
These techniques would be useful for visualizing flood elevations or other key features as well. James Wedding spoke of using the HEC-RAS extension (available on the subscription center) in his AU class called The Floodplain Truth: Civil 3D and HEC-RAS. In the class, he used a similar technique to build a corridor from flood profiles and make an exhibit.
Related posts:
Civil 3D Success Stories- Stream Restoration
Civil 3D Surfaces for Riverbed Elevations
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