How to create a flood plain - Tip and Trick

Ok, this is turning into a brain dump week

 

So to do this little technique we merely use a cut and fill method to find out where a given level would intersect the ground.

Step 1

Draw a rectangle over your surface

 
 

Step 2

Convert the rectangle to a feature line and assign it a constant level/elevation of what you require to check against

 

Step 3

Create a surface from this rectangle

  

Step 4

Create a volume tin surface comparing the ground to this flat surface

 
 

Step 5

Create a style which just shows a user contour only and set the layer, colour, lineweight etc and apply this to your volume surface

 

Step 6

Click on the volume surface and its properties and click on the analysis tab

Choose user contour, set one range and enter the value 0

Click Apply

 

Step 7

The line drawn is where the flood level intersects the ground surface

 

Step 8 - Change

So by turning on the rebuild automatic to your flood level surface and the volume surface, you can now select your featureline and adjust its level/elevation and watch how the flood extents take affect.

Fun, or scary depending if you live near the area affected!

Step 8 - Visualisation

Of course its nice to have a pretty picture of your work, so all we need to do now is restrict the flood surface to the contour line being drawn.

This you will need to extract the contour line from the volume surface, so select the volume surface contour line, extract objects and ok to the contour line.

 

Add this polyline to your flood level surface as a non destructive outer boundary.

(NOTE you may need to close the boundary like mine as the 0 level went outside my surface limits.)

 

Then using the techniques explained in my earlier post on boundaries and holes you can create a copy of your ground to cut a hole out of. Link to post

This will put your volume surface out of date also as you are affecting the surface it is based on, again make a copy of it if you prefer with the paste edit option.

Then of course set render materials to suit

 

Jack Strongitharm

 

Comments

[Sigitas]

Is it possible to do the same thing with Civil 3D 2010?

[Jack Strongitharm]

You can do this in any version of Civil 3D.
Only the drape aerial photo was specific to 2008 version.

Good luck

Jack

[MikeEvans]

Couldn't you just an user contour at the level required then extract it?

It should give the same result without the additional featureline & volume work.

[Jack Strongitharm]

Yes that would work also, just tried it.
Just set your surface style to user contour and in the analysis set the water level.

I guess my original method will also give you a volume which could be useful.

Thanks for your comments, always good to discuss methods and find the quickest and easiest route.

Jack

[Brian Hailey]

The user defined contour is great for those situations where the flood level is constant but, when the flood level changes along the river reach (pretty rapid in most parts around here), then the two surface method is the only way I know of to do this. The only caveat is it won't identify backwater areas.

[Fernando]

Amazing!!!!
Very useful and easy.
Thanks from Brazil.

Fernando

[Albert]

Hi, I'm using C3D 2007 , surface creation from the rectangle feature, there's no triangulation surface type other than Tin surface, grid surface, grid volume surface and Tin volume surface. Am I missing something. Thanks for your reply.

[Jack Strongitharm]

If you use the US English version it is the TIN Surface option. The British English version I use and control the glossary for, I changed the term to suit our location to what people are used to here.

Hope that is clear

Jack