London's artificial wet docks would be an example although they were more designed to provide secure space off of the main river rather than because of the speed of the Thames (So slow it flows backwards at times). I expect any river where the speed of the flow is a significant problem probably isn't going to allow passage of large ships that would need any significant port infrastructure, although I'm not an expert on this.
London's docks are just big, generally rectangular lakes attached to the Thames by canals.
London Docklands - Wikipedia, the free encyclopedia
London is built on a big, flat, easy to dig floodplain. A "tumultuous" river is going to be in terrain that's much less amenable to digging artificial lakes at river level. More rock and much less flat.
It would make more sense for a large river port to be as far up the river as possible before it becomes hard to navigate for large ships, at which point artificial wet docks would make sense to provide a secure, off river place to moor ships, just like in London. On longer rivers, the ports might be staged, with a port for ocean going ships as far along as they could navigate, then ports further up for large river boats. I expect this was the case but I don't know the details off hand. It would be worth doing a bit of research into medieval river travel.
The other thing to consider is bridges. IIRC, London is situated at the point where the Thames first becomes practical to bridge (at the time it was founded). Bridges and large ships don't mix particularly well, particularly with medieval technology. So the first bridge will tend to restrict the location of a port (hence the Port of London). Movable bridges or really tall, wide span bridges aren't possible without relatively modern materials and engineering. Rivers would tend to be crossed with ferries more than bridges.
Throwing in some magic (Dwarves built it), can mitigate some issues but it's usually best to do so in moderation, and knowing that you are doing so.