Hydrographic (?!?) question: artificial river port

[Caenwyr]

Sorry, I wasn't clear. The idea is that the river was flowing normally on the surface stratum of soil, which it slowly eroded, so that at one point, where the bedrock is closer to the surface for any reason, the bedrock gets exposed. I'm not trying to have a river flowing uphill or something.
Besides, scrap the bedrock, if a river course is narrowed by one or more islands at a certain loin, should not it become more turbulent anyway?

You'd think so, indeed, but actually no. A river's discharge remains roughly the same before, at and after a narrow stretch. Which means it will simply be deeper where it's narrower (if not water would build up behind it, forming a lake).

I think I've found the solution, however. There are rivers that are very large and yet pretty turbulent. All you'd need is a relatively sharp drop (say, a few 100 meters over a distance of a few 100 kilometers). The lower Congo River is an excellent example of that, it turns out. If you want to know more, be sure to check out this website.

[feanaaro]

Interesting. So we could sum up by saying that turbulence depends exclusively on the sharpness of the drop, while, for a given flow rate, depth is inversely proportional to width.
Is that right? I'm not terribly wed to the turbulence thing, if islands narrowing the river make it deeper that might actually be good for a port in itself, without needing much channeling.