Here's the situation:

We have this land with a small creek running through it. It's all wooded and there are paths, and it's beautiful, and there are three small waterfall-type areas in the creek. Ten years ago, the best of the three was at least ten feet high, from the top of the slate creekbed up above to the rocks under the water, and even the tallest could stand under there for a lovely little shower. There were even fish down below!

Since then, though, this crevasse with slate walls has gradually filled with rocks from farther up the creek, so that it's now only about 5 feet from top to bottom, and only wading and wettening of the hips are easy. I want to basically dig it out. It would be removing 5-7 vertical feet of layered rocks and creekbed from a channel about 3 feet wide and 20-30 feet long.

By hand, a massive undertaking, lots of heavy lifting, time, and possible injury. No heavy machinery, 'cause it's inaccessible (and would mess up the woods anyway). Possibly some sort of simple water-powered device. How can I do this? My thought have been:

1. Use an adjustable dam sort of thing, with 4x4's holding the water back. Let it get high, and then release it all. Repeat and lower the damming apparatus as needed. This would just use the built up water to wash the stones downstream. Maybe no place for them to go very far?

2. Waterwheel attached to some sort of a screw mechanism or scoop to push rocks downstream. Where to get a big funky screw like that? What kind of machine could I just construct and leave there to do its work?

Any suggestions would be much appreciated.