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.
The most important aspect of a curtain drain (also known as a French drain) is make sure it's properly pitched.
So when building a curtain drain, it's critical you achieve the right slope and have it drain to daylight - in other words, not to a sump pump or anything of that nature. The reason the trench is typically 12 x 12 is so you can have room to get that slope just right and also so the perforated pipe isinvisible when its done.
But if you're okay with the pipe being seen, sure - 8 inches should suffice, and should effectively help drainage in your yard. That said, if you can dig 8 inches, why not just dig four more inches? The more stone surrounding that trench, the more effective it will be.