Taper edge for a smooth 'lemon wedge' indentation on the face of a box

[MargaritaErem]

Hello,

I am a complete newbie- been using AutoCAD for 3 days with a free trial that I got for a one time project. I'm sorry if this thread is a repeat of other topics- my searching ability is limited because of my lack of knowledge of terminology.

 

I need to create a 3D model of a segment of a jogging path/trail that has a drainage feature called a knick. I pasted a freehand drawing of what a knick looks like below this post. It's a semi-circular area that slopes to one side at a small angle on a trail that is otherwise flat. I need a model of a trail segment with two of these sloping indentations that is just a smooth, gray object- nothing fancy. I managed to create a simple 3D model for a second trail design that has a slope to one side throughout the trail- made a box with a tapered edge and rendered it gray.

 

Since to my eye a knick looks like a lemon wedge indented into the face of a box- that's what I've been working towards. Made a box, made a cylinder, moved the cylinder so half of its base sits on top of the box face on which I want the indentation, and then used pushpull and subtract to take out a shallow semi-circular cut off the top of the box (did two of these about 20 units apart on the same face).

 

Here is where I ran into my own limitations. I don't know how to taper the semicircular cut so that it actually slopes off the face to the edge and doesn't look like a clean cut depression. I need it to slope to the edge at a 2% angle. I've tried tapering many times, but I don't think I completely understand the concept of the tapering axis (or rather I know that I completely misunderstand it) because all I end up doing is tapering the various faces of the box and the knick cut stays the same. I also tried out all the tools on the ribbon that look like they can be used for filling in or smoothing edges, but without any luck. Can someone point me in the right direction on this tapering process? Or should I be approaching the process of making the knick from a completely different set of commands?

 

I am sorry I can't attach what I've done so far- I don't seem to have uploading ability.

 

I appreciate any help or advice.

Thank you.

-Margarita

 

knick: