heckler, i see you deleted your post in response to thad's. why not let the water run to where it wants at the bottom of the rock and put in a french drain or a grid to take the water to the out side and to a ditch that would need to be dug to get the water off the trail.
Why not ask Peter? He's the one who did the work. Peter probably did it as it will less work in the long term and debating his reasoning on a BB is really funny.