I'm about 4-5 feet deep into this exact project right now. I was digging it by hand before the ground froze (Northern Michigan (USA)), but I'll pick back up once spring rolls around. Our designs are pretty similar, except mine is only illustrated on the pages of my mind. I've encountered pooling water, which was mildly surprising (hilltop living, basement is woodframed with no problems....), but I'm guessing the 150% of normal precipitation levels might have had a hand in that. I'll be piping the excess water to a lower aquaculture site. I've sorted the excavated soil as I've worked - top soil for other projects, clay for other projects, mixed clay/sand/gravel I used to make a sledding hill for my youngins. I have no regrets about choosing to dig by hand. It was great exercise for me, and I learned a lot about the soil in that area. Best of luck. I keep waiting for people to tell me I'm stupid, but people seem to be waiting to see how it turns out.
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