I was able to create a label that labels the total length of the poly line for Time of Concentration Calculations.
I would like to add a component for the total vertical drop along the 3d water drop poly line.
2014 - Added in 2015?
I am pretty sure you can't create such a label for the polyline directly since Autocad only provides such data for each segment between vertices. What you could do is stike a no-plot 3D line between the end points, label it with a piece of text using a field and move the text to wherever it suits you along the polyline. Any time you need to update, move the end points of the line to the new locations and re-align the label.
There are other solutions no doubt but this might get you thinking along different paths for a solution.