The best I can guess is that you are looking for the word "ravine", or possibly "gully".
A crevice.
a moat
Ditch .
a moat
a moat
a moat
a moat
If no shelter is available lie down in a ditch.
a moat
Lie in a ditch or depression in the ground if you cannot get to shelter.
Lie down in a ditch or depression in the ground and cover your head.
Another word for a deep ditch that is dug around a castle is a moat. You could call it a trench, or you could fill it full of water and call it a moat.