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Valued Contributor
Posts: 75
Registered: ‎02-20-2008

# Re: Possible to create a surface that uses the highest elevation of two surfaces

09-28-2011 03:07 PM in reply to: AllenJessup

Glad to see so many people thinking about my question.  The reason I asked was because I was hoping for an easy way to determine the tidal prism for a marsh.  In this case the tidal prism is the volume between the MLLW and the MHHW.

I have the surface for the marsh topography.  I was going to create two more surfaces as planes, one for the MLLW elevation and the other for the MHHW elevation.

I wanted to "clip" the marsh topo with each of these surfaces to create two new surfaces.  One representing the site at low tide, the other at high tide.  From there I would do a comparison surface to get the volume difference.

I just couldn't figure out how to do the "clip" surfaces easily.  Yesterday I wasn't thinking of it in terms of clipping, but now that I am perhaps someone will come up with a really easy way to do what I am asking.

In the end I ended up creating two volume surfaces, one for the volume between the MLLW and the topo and another for the MHHW and the topo.  I then took the difference of the two fill values to get the tidal prism.

Erik

Distinguished Mentor
Posts: 664
Registered: ‎07-30-2008

# Re: Possible to create a surface that uses the highest elevation of two surfaces

09-28-2011 08:11 PM in reply to: erik

From each of your plane surfaces, turn the border display on, then extract the border from the surface. You can then use this to clip a copy of the marsh surface to create your two surfaces for volume calculation.

If this fixed your issue, click on "Accept as Solution"

Andrew Puller
Maitland, NSW, Australia
Windows 7 Enterprise 64bit
Intel core i7 2600 @ 3.40 GHz with 16GB Ram
Civil 3d 2013 64bit
Mentor
Posts: 154
Registered: ‎05-13-2010

# Re: Possible to create a surface that uses the highest elevation of two surfaces

09-29-2011 06:04 AM in reply to: erik

Easier solution then.

a) use bounded volumes

b) make a flat boxed feature line bigger than (or = to) your area of interest with elevation=LW, then HW, creating a flat surface by adding the feature line as a beakline to an empty surface.

Compute a volume between your marsh surface and your LW, and then again your HW. Ignore the cut volumes, using only the fill (vol between lower marsh surface and higher LW/HW surface). The cut volume is where the marsh is above your water levels and should be insignificant. Break out a calculator and take the difference.

Eric Collins, P.Tech.(Eng.)

Win 7 Pro SP1 64 bit
Intel i7 3770 @ 3.40 GHz
16 GB RAM
Civil 3D 2014 (IDSP)