Well, I did the work today. These pics would have had more impact if you could see a "before" photo, but I didn't think to take one. Here's the "after" anyway.
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In the 3rd photo from the left, you can see where I graded the hill a little bit. At the bottom of the hill, there was a steep drop-off, which you can kind of still see in the grassy area to the left of where I was working. I backed up to the drop-off and dropped the box blade and just cut it down and dragged the spoils into the low part. That's been bugging me for a while and it was nice to fix it.
Joshua... If you are cutting too much raise up the rippers and lengthen the top link. Put the rear blade and front blade flat or slightly angled back this will allow you to skim the surface and get maximum smoothing and scooping up loose dirt/ high spots without cutting in.
In this case, I really wanted to be digging in as much as possible, and shortened the top link nearly all the way. My goal was to create as smooth a sub-layer as possible. The pigs have created wallows in the clay, and I didn't just want to dump loose dirt in them, for it to wash away again, and to have a hard-pack area close to the surface. I bladed a few passes and then pushed the loose dirt back over the area, followed by a light tilling to break up clods, and seeded it with buckwheat (just because I had some leftover seed laying around). The photos are after blading and before tilling.
Honestly, there are some areas that I think are just going to be hopeless. There's nothing at the surface but rock-hard clay. I can't imagine any seed taking purchase or any water soaking in. It's certainly not worth having topsoil brought in if pigs are just going to ruin it again in a few months. I don't think there's really any way to keep it from washing away.
Rinse and Repeat.
I believe he is suggesting more building up, although with a clay base already there I would think of it more as moving some clay to build a short dyke. Either use the natural slope at the bottom or grade so it slopes the way you want, build a dyke at the end with an overflow and drain(this could be as simple as breaking the dyke and replacing when the time comes). When it rains, water and sediment run off, sediment falls to the bottom, and water flows out the overflow. Pigs leave, drain the area, let muck dry, and then spread/grade it.
Yea build up if you had to. Whichever works for your situation. You'll lose a lot less soil if you are catching it at the bottom of the grade.
The only downside would be that the urine from the pigs would buildup too but that might only be a real issue if you have a bunch of them. But worse case maybe drain out the liquids a little more often.
Just a thought I had. They do that a lot around here with the mines and construction sites to keep the run offs from getting into the water systems around here.