I live in a town on top of a hill in south central Pennsylvania – just outside a town famous for a flood. My backyard has so much water in it that I can't let my dogs run. The problem is, the yard's all clay and is not accessible by machine. Do I have to go twelve inches deep and twelve inches wide when digging a trench for a curtain drain, or can I dig merely enough to cover the pipe? My main problem is rainwater run-off.