Templates - Ditch Modeling With a Set Depth and Width From Backslope

Work backwards.  Since the location of the ditch relies on the location of the catch point (or daylight point), find that point first.  Create some null points that mimic the geometry of your ditch, starting at the hinge point or somewhere along the fill slope.  From the last of those null points run an end condition (not triangulated) to find the catch point.  Place your ditch working back to the road, with the last segment tying back to the hinge point.

6266.ToeDitch_SS2.itl

Work backwards.  Since the location of the ditch relies on the location of the catch point (or daylight point), find that point first.  Create some null points that mimic the geometry of your ditch, starting at the hinge point or somewhere along the fill slope.  From the last of those null points run an end condition (not triangulated) to find the catch point.  Place your ditch working back to the road, with the last segment tying back to the hinge point.

6266.ToeDitch_SS2.itl

Ray, this is exactly what i was looking for thank you for your help! 

I've watched videos that try to explain this that are far less clear than this single diagram. Bravo, Ray! 

So if the OG is quite variable along that ditch line, how to you get the ditch to grade/slope in one direction without it changing slope directions several times? As the template rules to create a 1 foot depth ditch minimum as I understand.

This method does assume relatively smooth terrain.  For variable terrain, it seems to me you will need either a designed ditch-bottom profile or a controlled depth from the shoulder hinge point (SGSh in diagram).  I would probably use this method to get the minimum ditch depth, project to the centerline profile and design a profile from there.

Agreed.  It's almost always the case that ditches will have their own profiles.  One can model the ditch as part of the roadway corridor model (which seems to be the case in this post), or one can model the ditch using an  independent corridor model that is ruled to the roadway corridor model.  This offers many advantages, especially in the very common situation where different people (or even different departments of an organization, or different companies) are designing the road vs. the ditch.  In that case, there are at least three different approaches I've used:

1. Use the toe of fill slope (catch point) from the roadway corridor model as the controlling alignment for the ditch corridor.  This works best when the linear feature for the catch point is relatively smooth with mild deflection points.  The initial ditch created from the template will have a constant depth.  You can then apply point controls to the inside bottom of ditch to create the ditch profile.  Since the centerline "floats" and is created by the corridor model for the ditch, you can use the Elevation and Grade method to create the profile for the centerline.

2. This is a modification of method #1.  Instead of using the roadway corridor model fill catch point feature directly, you create a new horizontal alignment along that feature, which you can rule to the roadway fill catch point feature where you want to create dependency by snapping.  This allows you to go back and insert horizontal curves or make other adjustments to account for deflections in the fill catch point feature that result in crossing templates in your ditch corridor model.

3. Create an horizontal alignment for the ditch centerline and apply a profile to it directly.  This method works best when there are very significant deflections in the fill slope catch point feature as well as significant changes in elevation.  This gives you maximum flexibility but will typically require more iteration to refine the ditch location and profile.