Alluvial channels


Hi everyone,

How would I go about selectively modelling active alluvial channels within the upper alluvial/colluvial layer of my model.

In my drilling data the alluvial material is just logged as a single unit but I do have GIS layers that I can use to delineate the channel margins. I also have a high res DEM as the top of my model which shows these channels very clearly.


Essentially all I want to do is differentiate these channels within my upper alluvial layer as a separate surface.


I’ve tried creating an erosional surface with the channel polygon as the basis but this doesn’t work.


Is there a typical way that this situation should be approached?




  • Hi Rick. Did you receive any feedback? I'm facing a similar issue and was wondering if you received any good advice or figured out any workarounds. Thanks. Chris Pantano
  • SeanBuchanan
    SeanBuchanan Posts: 17 mod
    edited February 2023
    Hi @RickJones. I find the easiest way to create channel deposits is by using Intrusion Surfaces. 

    Start by digitizing a GIS line around your channel deposit (or import your own).
    If creating your own GIS line within Leapfrog, Right click on GIS Folder- select 'New GIS Line' from Drawing. This will open up your Drawing Toolbar. Make sure you select the Green Polygon with the Pencil Icon, since we will be drawling directly on a 3D object (your Topography). Trace the outline of your channel deposit and make sure it's CLOSED, then press the Save button. 

    ** The same process can be done with a Polyline. Same workflow but Right Click on your 'Polylines' folder rather than GIS Folder. 

    Now in your Geological Model, Right Click on your Surface Chronology-> Select 'New Intrusion' ->'From GIS Line', select your Channel GIS Line. This will create a channel / bowl shape for you. If your geology is flipped, go back to your polyline and change the polarity.
    This button is called 'Flip tangent/disks' and the Hotkey for this is 'V'

    Now you might want to control the bottom surface of the channel. You can do this with creating explicit edits to this surface. Right Click on the Intrusion Surface-> 'Edit' -> With Polyline. Then add points/normals/polylines in the scene to help control your bottom surface. You might find it easier to cut a Slice through your channel and make edits by Drawling on the Slicer. 

    Really intricate channel/QAL deposits can be quite tricky.

    Something you could also consider is taking your closed polylines  nd creating an extruded meshes out of them, however these surfaces will be quite blocky but can sometimes fit the bill. Right click on your Meshes Folder-->'New Extruded Mesh'-->'From Polyline'. Select your closed polyline object. From here, you can extrude the polyline by a distance up or down. Select the "close volume' check box. This will create a closed volume/extruded mesh in your Meshes folder. Add this to your GM by creating an 'Intrusion' from the Extruded Mesh surface. Mesh