The trench is more for access than drainage. With that much clay you'd think it would puddle but it perks right through. When I enlarge it I'll put a step-down at the door to let cold air drain out. There's something about that in one of those videos Greenfin linked to.
The berm is part of the design. It collects heat from the sun during the day and radiates it back at night. Water is a much more efficient heat collector, but that takes expensive containers and you have leaks and algae growth to worry about. I scraped the topsoil off and set it aside. When I finish the berm I'll lay a layer of plastic as a moisture barrier, spread the topsoil over it, and plant grass. After a winter of rain and freeze/thaw that clay will be settled against the barrier. I'll be able to take the barrier out, use it to form the next section, and replace it with a light framework to support the roof. That clay will hold it's shape as long as it stays dry. You'll notice that I used very little bracing to hold it while I was back filling. I couldn't have braces over the hole and dig with the backhoe so I had chains anchored to stakes on the north side.
The yellow chain stands out but there's another one down at the end. I was careful to just pour the dirt in, and not push on it, while I was back filling. I've already removed them and just have the three 2X4 braces on the South side and it's holding okay.
If you have enough land to justify a tractor you should think about getting a loader and backhoe with it. That was one of the best investment I've ever made. I was (still am) planning to build a rammed earth house. That hasn't happened yet, but I've dug enough footers, ditches, drain fields, and now this. to pay for it. I've turned compost with it and taken it to the sawmill to load free scrap wood on my trailer. If you rent the equipment it's expensive, you have the hassle of pick up and return, and you're under pressure to rush the job.
I would consider one like this even if I had a small plot of land. It lets you garden year round. With kiddy pool sips or a rain gutter system you can grow an awful lot of stuff in a small space. As long as your water table is deep enough that it won't pool, you'll have it covered anyway, you can divert water away, and put the moisture barrier all the way around so it doesn't seep in after a hard rain. Put steps in for access in a well under the roof.
There's a lot of good ideas in the permies forums