Cutting a "channel" halfway into a shape? What I mean:



How can cut this groove? 

The "channel" doesn't go all the way through, probably only half way or so (Using a picture to build my model so I can't tell for sure). It's suppose to be a height adjuster like you would find on a lawnmower for the height of the blades. was wondering if I could use the boolean modifier but I didn't know if one shape has to go all the way through the other shape for the modifier to work properly.

What do you's think?
You can use knife project.

By hiding the faces you don't want to cut, you can control which faces get cut with the shape and which are left uncut.

Example:

With the shape object selected,  Shift-Select the object you want to cut and enter edit mode:



Select the bottom faces (the ones you want to preserve with no cuts) and Hide them (H)



Then in top orthogonal view press the Space Bar and type Knife Project. Enable Cut Through** and then unhide the hidden faces (AltH)