How about Creeping Jenny? It seems to be pretty sturdy stuff - I have it growing in my artifical stream. (admittedly the current can't move cinder blocks) The only problem is that it really takes over!

I'm thinking more in the line of ferns, small shrubs, cannas or elephant ear etc.

I'm sure the depth of the fast water near the edge would make a difference. The blocks were at the bottom of the creek which remains swift for hours to a day after, depending on the type of storm, but some of the edges where I'd like to plant may get flooded only several inches during the rain and some only for several hours after a storm. Because we're down stream of a culvert-the creek only gets as high as the culvert can hold. If we were up stream that would be different.

I'm thinking the length of time to establishe roots, would be crucial. How could I protect something until it became established? Is there some kind of mesh that could be placed over the roots

"Is there some kind of mesh that could be placed over the roots"

My first thought was chain-link fencing.

If we knew what part of the country you were in, we might be able to suggest appropriate plants. Elephant ear & canna seem pretty fleshy, more likely to shred. It sounds like you need something tough.

Sue