During the winter there are some creeks that are always flowing. Black canyon, Big bug, Humbug. There are also a lot of smaller creeks that flow with the snow melt. I found a 3.25 oz nugget 5 feet down in one of them back in the 80s. That was with a 3" and I still had to run the water over the top of the hole with pipes.
As far as regulations. I know on club claims you must refill your hole. Which is odd as the water/gravel fills it in anyway. I have not heard of any regulations as to the size. You may try and contact the Arizona GPAA and ask them.
Tom H.