I remember the riverbeds Foo'bar is talking about. They were shown in the Storm of War preview DVD that came with IL2 1946.
I had a trawl on YouTube and found the said video. The river bit is at 4:10.
There is a lot of other things "previewed" in this video, and I take no responsibility for any "what happened to this or that feature" whines that may result.
Sorry guys, I've had to edit my post.
I tried to embed the youtube player into my post but it didn't work.
So here is the link;
How do you embed a youtube video anyway?